Exercising While Breastfeeding

A reader recently asked whether exercise — specifically marathon training — affects lactation and breastfeeding. I did a little digging and came up with some information, but decided the article fit better at another site for which I write: Trail and Ultra Running. Here’s a brief summary of my findings, based upon the current research:

  • Moderate exercise (about 45 min/day, 5 days/week, moderate intensity) probably has no negative effect on milk production
  • Short-term vigorous exercise probably has no negative impact on milk production
  • Habitual moderate-volume exercisers may make slightly more milk than sedentary women
  • Exercise that results in short-term (~2 weeks) significant caloric deficit probably has no negative effect on milk production
  • There’s no evidence that habitual moderate exercise negatively impacts nutritional content of milk or immunologic factors (like antibodies)
  • Moderate exercise doesn’t appear to increase the amount of lactic acid (a waste product of exercise) in milk, while intense exercise increases lactic acid in milk for about 90 minutes; this doesn’t affect nutrition, but may impact flavor
  • Infants may or may not respond negatively to temporarily increased levels of lactic acid in milk; women can pump before exercising if this is a concern
  • Lactic acid clears from the milk as it clears from the blood; there’s no need to “pump and dump” after vigorous exercise

Read the entire post here.


Breast Milk For Pain Relief

Image from Melimama, Wikimedia Commons

There are two interesting studies on breast milk as an analgesic (pain reliever) in this month’s issue of Pediatrics. Each compares the effects of breast milk to those of oral sugar (either glucose or sucrose) for relieving pain during the ubiquitous neonatal heel stick procedure.

The first study looked at late preterm infants (gestational age 34-36 weeks), and measured pain as indicated by crying and pain response (evaluated using the Premature Infant Pain Profile [PIPP] scale) [1]. All infants were being breastfed and were fed at least an hour before the procedure. They were randomized into two groups, one of which received expressed breast milk (from the infant’s mother) and one of which received a solution of glucose. (Glucose is a type of sugar; it’s exceedingly common in nature and in food, but is only about 70% as sweet as table sugar. Sugar solutions have been well established as a method of delivering pain relief to neonates [2]). The researchers found that infants given glucose displayed significantly less discomfort during and after the procedure compared to those given expressed breast milk. Interesting though these results are, they don’t particularly excite me. They can be taken to mean oral glucose is a superior analgesic to oral breast milk in late preterm newborns, but they can’t be taken to mean oral glucose is a superior analgesic to breastfeeding in late preterm newborns. This is because breastfeeding consists of more than simply oral administration of breast milk.

I’m more interested in the findings of a second study, also conducted on late preterm infants undergoing heel stick [3]. In this study, breastfed infants were randomized to one of three conditions: oral sucrose (table sugar) solution, expressed breast milk, or breastfeeding. Infants were fed or given sucrose during the heel stick procedure. Those being breastfed were held in their mother’s arms, while those receiving expressed breast milk or sucrose were held by a nurse. As in the first study, the researchers measured crying and pain response via PIPP. There was no significant difference in PIPP score for infants receiving breast milk versus those receiving sucrose. Interestingly enough, this was true for both the expressed breast milk group AND the group being breastfed. I have to admit to being surprised by the results; I would have guessed that there would be no difference between sucrose and expressed breast milk (or possibly that sucrose would be more effective), but that breastfeeding would provide superior analgesia!

Note that these results apply only to neonates (and, to be rigorous, only to late preterm neonates). It’s entirely possible that the establishment of a solid breastfeeding relationship over the course of the first weeks or months of life would change the relative efficacy of sugar solution versus expressed breast milk versus breastfeeding as analgesics (follow-up post on this issue forthcoming).

One final note — in the discussion portion of the second study (where the researchers talk about what their results mean and what they noticed while doing the study), there was a line that jumped out at me. The researchers were apparently, like me, surprised that they didn’t discover that breast milk was a superior analgesic. They suggested that one reason could have been that preterm infants have an “immature competence for sucking,” which could have reduced their ability to take enough milk to make a difference. Further, they noted (and this is what caught my eye), “We observed that these [preterm] newborns are more easily annoyed than term neonates…” Alrighty then!


Science Bottom Line:* In late preterm newborns, sugar solutions provide pain relief for procedures such as a heel lance. Breast milk, either expressed or obtained via breastfeeding, may provide similar pain relief, though some evidence suggests that breast milk is not as effective as sugar.


Do you think breast milk helps relieve pain?



1) Bueno et al. Breast milk and glucose for pain relief in preterm infants: a noninferiority randomized controlled trial. Pediatrics. 2012 Apr;129(4):664-70. Epub 2012 Mar 5.

2) Harrison et al. Efficacy of sweet solutions for analgesia in infants between 1 and 12 months of age: a systematic review. Arch Dis Child. 2010 Jun;95(6):406-13. Epub 2010 May 12.

3) Simonse et al. Analgesic effect of breast milk versus sucrose for analgesia during heel lance in late preterm infants. Pediatrics. 2012 Apr;129(4):657-63. Epub 2012 Mar 5.

When Is The Best Time To Introduce Solids?

The decision to start solids is both an exciting one (your baby is growing up!) and a difficult one for many parents. The latter is because there’s so much conflicting information floating around (“Starting solids sooner will make your baby sleep better!” “Starting solids too soon will give your baby allergies!”). The purpose of this post is to summarize the research that addresses when to start solids in a baby that is breast- and/or formula-fed.

If you’re confused by all the seemingly conflicting information out there regarding when to start solids, you’re in good company; the American Academy of Pediatrics (AAP) is split on this issue. The AAP’s Breastfeeding Initiatives state that it’s best to wait until an infant is 6 months of age, while the AAP’s nutrition division suggests that it’s fine to introduce solids around 4 months of age. There is no research to suggest that there’s any benefit associated with introducing solids before 4 months of age, and there is quite a bit of research suggesting that such early introduction of solids is associated with increased risk of allergies and eczema (see, for instance, Greer et al, Tarini et al, Zutavern et al). Waiting until 6 months of age to introduce solids decreases the risk of atopic diseases (allergies, eczema, and asthma). Researchers are split on introduction of the most allergenic foods (including eggs, shellfish, and nuts). Some studies (including Filipiak et al) suggest that there’s no benefit associated with waiting beyond the sixth month to introduce these foods (in non-chokable form), while other studies (such as Fiocchi et al) suggest waiting to introduce dairy, egg, nuts, and seafood. Given the split nature of research findings on delayed introduction of highly allergenic foods, it may be worth delaying such foods in families with a history of atopic disease. Highly allergenic foods aside, the preponderance of evidence suggests that the best time to introduce first solid foods falls somewhere between 4 and 6 months of age. The question, then, is whether to shoot for closer to the beginning of that window, or closer to the end.

There are several arguments often made for adding solids to the diet earlier, rather than later. None of these, however, are supported by science. Perhaps the most common assertion is that adding solids will improve infant sleep. Several studies have examined this issue, and have found no sleep improvement with added solids (see, for instance, Macknin et al, Oberlander et al.) The Oberlander study looked at newborns, comparing sleep after a randomly assigned meal of water, carbohydrate, or formula. Water-fed infants slept less than formula-fed infants, while carbohydrate-fed infants (contrary to the common maxim) didn’t sleep as well as formula-fed infants. The Macknin study examined the effects of adding infant cereal to the nighttime bottle (a common practice thought by some to promote sleep) of 5-week-old and 4-month-old infants. The sleep durations of the infants given cereal were compared to the sleep durations of same-age infants given formula with no cereal; the researchers found no increased quantity or quality of sleep with cereal. There is no research support for beginning solids as a means of improving sleep.

Another argument used to support introducing solids at closer to 4 months than 6 months of age is that the older infants are (according to their caregivers) no longer satisfied by breast milk or formula alone. Because 4- to 6-month-olds have very limited communication ability, this is largely based upon speculation. For instance, some caregivers interpret a 4-month-old’s sudden interest in the food on an adult’s plate (or silverware) as an interest in eating. Given the opportunity, many 4-month-olds will grab food off an adult’s plate and place it in their own mouth, interpreted by some caregivers to mean the baby wants to (and/or is ready to) eat solids. However (and I recognize this is not a scientific statement), 4-month-olds also put rocks, garbage, and anything else they can find into their mouths. Around 4 months of age, an infant’s attention begins to turn to the outside world. The infant also increasingly possesses the ability to control his hands, allowing him to grasp objects of interest and bring them to his mouth for exploration. Infants don’t differentiate “food” from “non-food” with regard to what they taste; they simply use oral investigation as one of their means of gaining information about the world. It is a misattribution of intent to suggest that a 4-month-old who grabs food off his mother’s plate wants to eat solids. More scientifically, there is no evidence to suggest that an infant younger than 6 months of age needs anything more than breast milk (with supplemental vitamin D if indicated, see this article for more information) or formula. Further, there is ample scientific evidence showing that infants thrive on nothing but breast milk for the first 6 months (see, for instance, Carruth et al, Dewey, Nielsen et al). There is also evidence showing that introducing solids after 4, but before 6 months of age doesn’t positively affect growth (Cohen et al), because infants fed solids consume less milk or formula. Even infants given as many nursings (this study was conducted on breastfed infants) as they’d been given prior to introduction of solids consumed less milk per nursing when given supplemental solids. This demonstrates that a 4-month-old can’t be made to increase his caloric intake by giving him solids, as he’ll take less milk in response. Of particular concern is the case of the breastfed infant; there is no substance as nutritionally complete or suited to the digestive tract of the young infant as breast milk. Thus, since the breastfed infant responds to solids by decreasing milk consumption, supplementing with solids prior to 6 months of age actually decreases the quality of the breastfed infant’s diet. Given that formula is designed to mirror the nutritional qualities of breast milk as much as possible, we can reasonably extrapolate that it is the best second choice for feeding a non-breastfed infant (or supplementing an infant whose mother is not exclusively breastfeeding) until 6 months of age, and that introduction of complementary solids displaces a higher-quality source of nutrition.

If waiting until 6 months to introduce solids is good, then, is waiting longer than 6 months even better? Apparently not. There’s research that suggests rather strongly that delaying the introduction of solids beyond the 6-month point does not further decrease the risk of allergies (see, for instance, Filipiak et al, Greer et al, Zutavern et al), and may even increase the risk (Nwaru et al). Further, breast milk and formula are no longer sufficient to support increasing nutrient needs beyond 6 months of age (Dewey). As an isolated (but not unique) example, breast milk is quite low in iron (there is a great article about this at Science of Mom), and complementary foods can be used to increase iron in the diet (there’s another great article from Science of Mom here). The most nutritionally-complete diet for a 6-month-old (or older) infant should consist of mainly breast milk (or formula), with carefully-selected complementary solid foods.


Science Bottom Line:* There is ample research to support waiting until after 4 months of age to begin complementary solids, and there is a modest amount of research to support waiting until 6 months of age, particularly in the case of a breastfed infant. There is no evidence of any nutritional or behavioral benefit conferred by solids between 4 and 6 months of age. Research does not support (and, in fact, opposes) waiting beyond 6 months of age to introduce complementary solids.


When did you/will you introduce solids, and why?



Carruth et al. Addition of supplementary foods and infant growth (2 to 24 months). J Am Coll Nutr. 2000 Jun;19(3):405-12.

Cohen et al. Effects of age of introduction of complementary foods on infant breast milk intake, total energy intake, and growth: a randomised intervention study in Honduras. Lancet. 1994 Jul 30;344(8918):288-93.

Dewey, K. Nutrition, Growth, and Complementary Feeding of The Brestfed InfantPediatr Clin North Am. 2001 Feb;48(1):87-104.

Filipiak et al. Solid food introduction in relation to eczema: results from a four-year prospective birth cohort study. J Pediatr. 2007 Oct;151(4):352-8. Epub 2007 Aug 23.

Fiocchi et al. Food allergy and the introduction of solid foods to infants: a consensus document. Ann Allergy Asthma Immunol. 2006 Jul;97(1):10-20; quiz 21, 77.

Greer et al. Effects of Early Nutritional Interventions on the Development of Atopic Disease in Infants and Children: The Role of Maternal Dietary Restriction, Breastfeeding, Timing of Introduction of Complementary Foods, and Hydrolyzed Formulas. Pediatrics. 2008 Jan;121(1):183-91.

Macknin et al. Infant sleep and bedtime cereal. Am J Dis Child. 1989 Sep;143(9):1066-8.

Nielsen et al. Adequacy of Milk Intake During Exclusive Breastfeeding: A Longitudinal Study. Pediatrics. 2011 Oct;128(4):e907-14. Epub 2011 Sep 19.

Nwaru et al. Age at the Introduction of Solid Foods During the First Year and Allergic Sensitization at Age 5 Years. Pediatrics. 2010 Jan;125(1):50-9. Epub 2009 Dec 7.

Oberlander et al. Short-term effects of feed composition on sleeping and crying in newborns. Pediatrics. 1992 Nov;90(5):733-40.

Tarini et al. Systematic Review of the Relationship Between Early Introduction of Solid Foods to Infants and the Development of Allergic Disease. Arch Pediatr Adolesc Med. 2006 May;160(5):502-7.

Night Nursing and Cavities

Extended nursing is loosely defined. In the United States, where only about a third of babies are exclusively breastfed until 3 months of age and fewer than a sixth are exclusively breastfed until 6 months of age (per the CDC), one could reasonably claim that breastfeeding beyond a year is “extended.” The American Academy of Pediatrics recommends breastfeeding for at least a year (with complementary foods after six months of age), while the World Health Organization recommends at least two years. It goes without saying, then, that a baby breastfed per the recommendations of these organizations will still be breastfeeding when teeth have come in. Some lucky parents have babies who start sleeping through the night at only a few months of age, while other mothers find themselves nursing once, twice, or even multiple times per night well beyond a baby’s first birthday. Certain sources, including La Leche League, suggest that breast milk isn’t cariogenic (cavity-causing), and even protects the teeth. Others, however, suggest that breast milk pooling in a baby’s mouth leads to early cavities, which can have significant ramifications for later oral health. What does the science say about night nursing and cavities?

One problem with finding a scientific answer to this question is that it’s difficult research to do. Case studies — reports of medical findings in a given individual — provide a limited amount of information, but aren’t a strong platform from which to derive inductive generalizations. This is because it’s difficult or impossible to establish causality in the case of an individual. As such, while there are reports in the literature of nursing caries associated with breastfeeding, these don’t support the conclusion that night nursing causes cavities.

Stronger evidence that night nursing either is or is not associated with cavity formation comes from population-level analysis. Dentist Brian Palmer, who studies ancient human skulls, concludes that there’s no connection between breastfeeding and night nursing on the grounds that 1) there isn’t evidence of cavities in ancient skulls of children, and 2) these children were probably breastfed for an extended period of time. Unfortunately, there are several problems with his theories. First, he has no proof that children were nursed at night (yes, they probably were…but he has no proof). Second, he does not take into account other aspects of diet that could significantly impact dental health. The conclusion he can reasonably draw from his research is that nursing didn’t cause cavities in children 500-1000 years ago, but it’s not possible to generalize this conclusion to today’s children because of significant dietary and lifestyle differences.

A few studies have looked at populations of modern children in an attempt to determine whether night nursing correlates with cavities. A study of children in Tehran found an association between bottle-feeding with milk at night and cavity development, but no association between breastfeeding at night and cavity development (Mohebbi et al). A study of Swedish children found that it was the intake of cariogenic food that was most associated with early cavity formation (Hallonsten et al). This finding weakens the findings of the Mohebbi study where they apply to children in the U.S. and other Western industrialized nations, because of significant dietary differences. Hallonsten also found, interestingly enough, that children who engaged in extended breastfeeding were more likely to consume cariogenic foods and have other cavity-promoting dietary habits than those who weaned at younger ages. A study of Dutch children found that frequency of breastfeeding and lack of fluoride were most associated with development of cavities (Weerheijm et al).

Note that the experimental design in the studies above is not one that allows determination of causality, only correlation. It’s possible that parents who breastfeed at night also engage in or encourage behavior x (whatever that might be), which predisposes their children to (or helps prevent) cavities.

Cavities are, of course, complicated things. There are a multitude of factors that make them more likely (bacterial colonization of the mouth, intake of cariogenic foods), as well as factors that make them less likely (dental hygiene, fluoride). Perhaps the most important question to answer in order to inform the night nursing/cavities association is whether human milk itself is cariogenic. La Leche League claims it is not, but this appears not to be supported by any particular scientific evidence, as they cite no direct research on the cariogenicity of human milk. Research evidence, in contrast, suggests that human milk is mildly cariogenic, though far less so than sugar water or soda (Bowen et al). The researchers ranked the cariogenicity of various tested substances as follows: table sugar, 1; soda (cola), 1.16 (the acid probably contributed to the increased cariogenicity as compared to table sugar); honey, 0.88; human breast milk, 0.29; cow’s milk, 0.01; distilled water, 0. The authors speculated that the increased cariogenicity of human milk as compared to cow’s milk may be due to the greater concentration of lactose in human milk, and (likely more important) the much lower concentration of dental health-supporting minerals (such as calcium and phosphate) in human milk. Based upon this research, it is unreasonable to suggest that human milk is non-cariogenic.


Science Bottom Line:* Human milk is approximately 1/3 as cariogenic as table sugar, and should be treated as a mildly cariogenic food. It’s probably reasonable to consider brushing a child’s teeth after a night nursing session, or at least wiping them off with gauze.


What do you do to help prevent nursing cavities in your night-nursing baby or toddler?



Bowen et al. Comparison of the cariogenicity of cola, honey, cow milk, human milk, and sucrose. Pediatrics. 2005 Oct;116(4):921-6.

Hallonsten et al. Dental caries and prolonged breast-feeding in 18-month-old Swedish children. Int J Paediatr Dent. 1995 Sep;5(3):149-55.

Mohebbi et al. Feeding habits as determinants of early childhood caries in a population where prolonged breastfeeding is the norm. Community Dent Oral Epidemiol. 2008 Aug;36(4):363-9.

Palmer; B. Breastfeeding and infant caries: No connection. ABM News and Views 2000; 6(4): 27,31.

Palmer B. The Influence of Breastfeeding on the Development of the Oral Cavity: A Commentary. J Hum Lact 1998;14:93-98.

Weerheihm et al. Prolonged demand breast-feeding and nursing caries. Caries Res. 1998;32(1):46-50.

Breast Milk and Premature Babies

One of the most fascinating aspects of human breast milk is that the milk literally changes during the course of a nursing relationship. The earliest secretions from the breast — called colostrum — are high in antibodies and protein. Transitional milk comes in a few days post-delivery, and milk changes once again at around two weeks post-delivery. The changes in breast milk occur to meet the changing needs — and changing maturity — of the human infant.

A new study published in the medical journal Pediatrics reports on yet another phase of milk that occurs in the case of a premature delivery (Gabrielli et al). It appears that lactating mothers of premature infants (average age studied was just shy of 28 weeks gestational age) produce milk that is much lower in lactose than the milk produced by mothers of full-term infant.

Lactose is a small sugar molecule made up of two smaller sugar units, called glucose and galactose. To digest lactose, the human intestine uses an enzyme called lactase, which breaks lactose into its separate glucose and galactose components; these are then absorbed into the bloodstream and can be taken up by the cells for energy. While some adults are lactose intolerant, a condition that results from insufficient production of the lactase enzyme, this condition is very, very rare in babies. Premature infants, however, generally don’t digest lactose to the same extent as full-term newborns (see, for instance, MacLean et al, Chiles et al), largely because of reduced lactase activity until the ninth month of gestation (see, for instance, Antonowicz et al, Aurrichio et al, Dahlqvist et al). This reported finding — that breast milk for preemies is especially low in a sugar they find hard to digest — is simply another neat example of human milk conforming to the needs of the human infant, regardless of the circumstances.

Another interesting finding of the study dealt with some pretty technical genetic issues. Stated simply, there are larger sugars than lactose (collectively called oligosaccharides) in human milk, and there are quite a large variety of these larger sugars. While all women produce most of the oligosaccharides, production of some of them requires enzymes that not everyone has. Two different genes (they go by the technical names Le and Se, but we’ll call them Gene 1 and Gene 2 for simplicity’s sake) are involved; women with Gene 1 can make Enzyme 1, and women with Gene 2 can make Enzyme 2. As a result, there are four different types of milk resulting from four different possible gene/enzyme combinations. According to the study, about 70% of women have both genes and produce both enzymes. These women produce the largest number and greatest variety of oligosaccharides. About 20% of the population lacks Gene 1 and therefore lacks Enzyme 1, but has Enzyme 2. About 9% of the population has Gene 1/Enzyme 1, but lacks Gene 2/Enzyme 2. These two groups of women produce fewer total oligosaccharides and a smaller variety of oligosaccharides than women with both genes/enzymes. About 1% of the population lacks both genes, and therefore both enzymes. These women consequently produce the smallest total number and smallest variety of oligosaccharides.

Because oligosaccharides aren’t digested, generally speaking, they don’t contribute to the caloric content or nutritional value of breast milk (Coppa et al). Instead, they pass through the gut and act as soluble fiber, which helps to promote regularity of bowel movements and keep bowel movements soft. They also appear to help prevent pathogenic bacteria from adhering to the gut wall, which helps prevent infection, and they seem to promote the growth of healthy gut bacteria (Bode). Finally, because they pass into the bloodstream to some extent in undigested form (Rudloff et al), it’s hypothesized that they could play a role in immune system function, or act as precursors for a variety of important molecules including some involved in brain function. The milk from mothers of preterm infants appears to be especially high in oligosaccharides, according to the Gabrielli study, which the authors hypothesize is particularly important for these smallest babies. On the basis of their findings, the authors emphasize the importance of human breast milk, ideally from the mother and as opposed to formula, as a source of nutrition for preterm babies.  The authors further note that the differences between women in terms of oligosaccharide production, and the importance of a wide variety of oligosaccharides in milk, justifies the mixing of milk from donors rather than the use of single-donor milk should a baby require breast milk supplementation.


If you’re interested in donating milk, the Human Milk Banking Association of North America needs donations.


Which of human milk’s various properties interests you most?


Antonowicz et al. Development and distribution of lysosomal enzymes and disaccharidases in human fetal intestine. Gastroenterology. 1974 Jul;67(1):51-8.

Aurrichio et al. Intestinal glycosidase activities in the human embryo, fetus, and newborn. Pediatrics. 1965 Jun;35:944-54.

Bode, L. Human milk oligosaccharides: prebiotics and beyond. Nutr Rev. 2009 Nov;67 Suppl 2:S183-91.

Chiles et al. Lactose utilization in the newborn; role of colonic flora. Pediatr Res. 1979; 13:365.

Coppa et al. Characterization of oligo- saccharides in milk and feces of breast-fed infants by high-performance anion- exchange chromatography. Adv Exp Med Biol. 2001;501:307-14.

Dahlqvist et al. Development of the intestinal disaccharidase and alkaline phosphatase activities in the human foetus. Clin Sci. 1966 Jun;30(3):517-28.

Gabrielli et al. Preterm milk oligosaccharides during the first month of lactation. Pediatrics. 2011 Dec;128(6):e1520-31. Epub 2011 Nov 28.

MacLean et al. Lactose malabsorption by premature infants: magnitude and clinical significance. J Pediatr. 1980 Sep;97(3):383-8.

Rudloff et al. Urinary excretion of lactose and oligosaccharides in preterm infants fed human milk or infant formula. Acta Paediatr. 1996 May;85(5):598-603.

Glowing Green Milk

Mammograms aren’t fun for a variety of reasons. Perhaps the most obvious is that they involve smashing the breasts between two plates so that they resemble — as much as is possible for semi-spherical body parts — pancakes. I have a mammogram coming up shortly, and to be honest, I’m less concerned about the former, and am more bothered by the fact that I’m old enough to be on my second mammogram. Apparently, however, doctors don’t like it when mammograms converge with lactation in space-time. For instance, the health provider who prescribed my upcoming mammogram told me, “You may want to pump and dump afterward, because of the radiation.” When I actually called to schedule the procedure, I was told that they would be doing an ultrasound instead, because I was lactating and they didn’t want to “expose my milk to the radiation.”

Now, I teach chemistry, so I’m well aware of how common are fears and misconceptions about radiation. I have to admit, however, that I didn’t think doctors’ offices would share (or propagate) those fears and misconceptions. In any case, I thought it would be worth addressing why mammograms (and MRIs, and x-rays) won’t make your milk glow green (as cool as that would be), and why you don’t need to pump and dump if you have to have one of these procedures. (Incidentally, Kellymom has lots of information on what is and what is not safe during lactation.)

We tend to think of anything called “radiation” as being bad, and generally associate exposure to radiation with things like cancer, Chernobyl, and Spiderman. Thankfully, most radiation can’t produce cancer, and unfortunately, no radiation has the ability to produce Spiderman. “Radiation” is really just a term for radiant energy, which is even more technically referred to as electromagnetic radiation, or EMR. EMR encompasses many different types of phenomena that we don’t necessarily think of as related to one another. These include — but are not limited to — x-rays, visible light, and radio waves. Without getting too deep into the physics, all EMR has a frequency, and the frequency of the EMR determines the type of radiation. It’s possible to draw a limited analogy to sound here; the pitch of a sound is a function of its frequency, so frequency determines the “type” of sound. The analogy between sound and EMR doesn’t take us far, however, and the important point here is that high-frequency EMR has high energy.

From Wikipedia, Philip Ronan

The reason all this matters is that some EMR can interact with molecules, and the way EMR interacts with a molecule depends upon the type of EMR. Think of a molecule as being made up of particles (called atoms) connected by springs (bonds). The springs (bonds) naturally bend and stretch, and very high energy EMR can “overstretch” the springs and make them break, like this:

From Hendrickson, K. "Chemistry In The World" 2010.


Break the bonds, and you destroy the function of the molecule. If the molecule that gets broken is, say, DNA — your genetic material — then bad things happen, including disease, cancer, aging, and so forth. The only types of EMR with enough energy to break bonds in molecules are UV light, x-rays, and gamma rays (collectively called “ionizing radiation”). These are the only types of EMR that, consequently, can cause cancer and so forth (note that despite their bad reputation in some circles, microwaves have completely insufficient energy to cause cancer). Ok, so x-rays can cause cancer, as can mammograms (which rely upon x-rays). MRIs can’t, since they don’t use ionizing radiation, and rely instead upon the behavior of atoms in a magnetic field.

If x-rays fall into the category of ionizing radiation, why shouldn’t we worry about the milk that gets shot full of x-rays? The answer to this is simply that very, VERY few phenomena can actually make things radioactive. X-rays, and even gamma rays (which come from nuclear reactions and can cause a variety of cancers, radiation poisoning, and so forth) can’t make the things exposed to them radioactive. If you were exposed to nuclear fallout (like from the Chernobyl disaster), you could temporarily “become radioactive,” but only because nuclear fallout includes bombardment with subatomic particles called neutrons (among other things). If you have certain types of radioactive material introduced into your body, you can emit radiation due to the presence of the radioactive material. However, it is impossible for you (or your fluids) to become radioactive as a result of x-ray exposure. The only thing the x-rays could theoretically do to your milk would be to break down some of the proteins and other molecules (though they’re unlikely to, because the dose is so small), and furthermore, this wouldn’t affect the quality — or the safety — of the milk.

I Googled lactation and mammography, because I wanted to know what it was (assuming most medical professionals know there’s no risk of radioactive milk from a mammogram) that would cause a health practitioner to put off a mammogram on a lactating woman (which, according to Google, happens quite often). It turns out that practitioners worry about the “goo-factor.” Breast milk is a bodily fluid, and apparently the staff of imaging clinics is concerned that it will, well, squirt on things. Not that it does, generally speaking…but regardless, this appears to be a major motivating factor with regard to lactating women and the medical profession’s desire to keep them, and their squirting milk, away from those hard-to-clean mammography machines.


Science Bottom Line:* There is no danger to your milk if you have to have a mammogram or x-ray while you’re lactating. There is, as always, some danger to you personally any time you’re exposed to ionizing radiation, which is why it’s always important to weigh the risks against the benefits when you need to have imaging done. You don’t need to pump and dump unless you’re engorged.


What medical procedures have you wondered (or worried) about during lactation?


Nitrates, Cancer, Lunch Meat, and Celery — Should You Worry?

Nitrates and nitrites are chemically related to one another, and are commonly used as preservatives in a variety of food items. Bacon is perhaps the most notable example, but many packaged, processed meats — including many lunch meats — are among those that contain nitrates and nitrites. Even “natural” lunch meats, which don’t list nitrates or nitrites on the ingredients label, can contain dried celery juice. This is a natural source of nitrates and nitrites.

First and foremost, nitrates and nitrites, while not chemically identical, are implicated in similar health consequences. This is because a chemical reaction converting nitrate into nitrite takes place in human saliva. Approximately 5% of ingested nitrate is converted to nitrite in the saliva of adults and children, while approximately 10% of ingested nitrate is converted to nitrite by infants (Spiegelhalder et al). The problem is that nitrites then go on to engage in a variety of undesirable chemical reactions. For one thing, they can react with chemicals called secondary amines to produce new compounds called nitrosamines. Nitrosamines are carcinogenic (cancer-causing) in animals (Swann et al), and there’s very good evidence — in fact, the relatively conservative Linus Pauling Institute of Oregon State University goes so far as to say there’s “an enormous amount of evidence” — to suggest they’re carcinogenic in humans as well (though of course, for obvious ethical reasons, no controlled scientific studies have been done). Secondary amines, put very succinctly, make up proteins, which in turn make up a major portion of the structural and functional componentry of every living cell. In short, living creatures have an abundance of secondary amines in the body, meaning that there’s no barrier to formation of carcinogenic nitrosamines upon the consumption of nitrites or nitrates. Meats are also made up of protein, which means a meat preserved with nitrate or nitrite salt contains all the necessary ingredients for nitrosamine formation.

Cancer-causing nitrosamines aren’t the only reason to be concerned about nitrates and nitrites; they can cause methemoglobinemia (“Blue-Baby Syndrome”) as well. This results from the reaction of nitrites with hemoglobin, which is the protein in red blood cells that binds to oxygen and carries it to the tissues. The reacted hemoglobin, called methemoglobin, can’t carry oxygen as efficiently. While one of the major causes of Blue-Baby Syndrome is consumption of formula made with nitrate-rich water by infants under 6 months of age (often water that is polluted by fertilizer runoff and other sources of nitrates), there have been reports in the literature of nitrites from vegetables leading to the syndrome (Sanchez-Echaniz et al). The Sanchez-Echaniz study reported on cases of methemoglobinemia in infants up to 13 months of age, which is troubling, but the vegetables in question were homemade purees that had been stored for some time (as opposed to fresh vegetables). Because there’s considerable evidence to suggest that nitrites and nitrosamines can cross the placenta (see, for instance, Gruener et al, Althoff et al), pregnant women are generally advised to avoid nitrate- and nitrite-containing foods during pregnancy. Interestingly enough, however, maternal consumption of high-nitrate water during lactation doesn’t appear to increase nitrate levels in breast milk (Dusdieker et al). The study did not report on nitrite or nitrosamine levels in breast milk, however.

Because a certain amount of exposure to nitrates and nitrites is unavoidable — they’re naturally-occurring, such that even avoiding processed food isn’t a mechanism for completely eliminating them from the diet — it’s more useful to discuss how much nitrate and nitrite is safe, rather than whether nitrate and nitrite are safe. The EPA standards for nitrates and nitrites in drinking water are set at no more than 10 mg/L and 1 mg/L, respectively. The dose of nitrate considered “safe” by the EPA is 1.6 mg/kg daily, while that for nitrite is 0.1 mg/kg daily. For a 15-pound baby (perhaps an average 6-month-old), that correlates to no more than 10.9 mg of nitrate and 0.68 mg of nitrite daily. Dietary nitrate and nitrite intake vary significantly with eating habits, but vegetables are the most major source of dietary nitrates in most individuals (White), providing just over 80% of total daily nitrate. Spinach, raw lettuce, and cooked beets are among the highest in nitrate concentration (van Velzen et al), with celery only slightly behind (White). All in all, an “average” adult likely gets about 86 mg/day of nitrate and 0.2 mg/day of nitrite from vegetables, in addition to 16 mg/day of nitrate and 3.92 mg of nitrite from cured meat. Given the 5% conversion, give or take, of nitrate in vegetables and meat to nitrite, the vegetables contribute a total of about 4.5 mg/day of nitrite, while cured meats contribute a total of about 4.72 mg/day of nitrite. This suggests that cured meats, while not the most significant source of dietary nitrates, are nevertheless the most significant source of dietary nitrites in most adults. If an average adult gets about 9.22 mg/day of nitrite from all sources (which is above the “safe” dose of 6.8 mg/day for a 150-pound adult), then clearly the average diet is a bit too high in nitrite for absolute safety’s sake. Because of the many health benefits associated with consuming vegetables, however, it isn’t reasonable to suggest reducing vegetable consumption (or even consumption of high-nitrate vegetables, like spinach) on these grounds. Cured meats, however, do not serve a unique and important dietary function, and it is therefore reasonable to suggest limiting cured meat consumption. Consuming a normal quantity of vegetables on a daily basis while reducing cured meat consumption to no more often than every other day is a reasonable mechanism for staying within EPA-suggested nitrate and nitrite limits.

The final question is whether nitrates and nitrites are any healthier if they come from celery as opposed to from added nitrate and nitrite salts. This is a bit difficult to quantify, because meat companies don’t report the amount of nitrate and nitrite in their product, but it’s reasonable to assume that the total quantity of preservative is probably similar, regardless of whether it comes from celery (as in “natural” meats) or from added sodium nitrate and sodium nitrite. Compared to a meat preserved with sodium nitrite, meat preserved with celery juice is probably safer. This is because the conversion of nitrate to nitrite is so inefficient, and because celery contains nitrate rather than nitrite. Compared to a meat preserved with sodium nitrate, however, a meat preserved with celery juice likely has very similar total nitrate concentration, as as such, there would be little difference between the two. These are speculations, but they’re reasonable and measured speculations.


Science Bottom Line:* Don’t cut down your vegetable consumption because you’re worried about nitrates and nitrites, but consider eating lunch meat no more than every other day. Be aware that there are nitrate and nitrite preservatives in some other foods as well (generally processed ones), so read packages carefully. Celery-preserved meats are probably better than nitrite-preserved meats, but may be quite similar to nitrate-preserved meats.


Do you watch for nitrates and nitrites in your diet?



Althoff et al. Transplacental effects of nitrosamines in Syrian hamsters: I. Dibutylnitrosamine and nitrosohexamethyleneimine. Z Krebsforsch Klin Onkol Cancer Res Clin Oncol. 1976 May 3;86(1):69-75.

Dusdieker et al. Does increased nitrate ingestion elevate nitrate levels in human milk? Arch Pediatr Adolesc Med. 1996 Mar;150(3):311-4.

EPA Drinking Water Contaminants. Accessed 1 Nov 2011.

EPA Nitrate. Accessed 1 Nov 2011.

EPA Nitrite. Accessed 1 Nov 2011.

Gruener et al. Methemoglobinemia induced by transplacental passage of nitrites in rats Bull Environ Contam Toxicol. 1973 Jan;9(1):44-8.

Linus Pauling Institute Nitrosamines and Cancer. Accessed 1 Nov 2011.

Sanchez-Echaniz et al. Methemoglobinemia and consumption of vegetables in infants. Pediatrics. 2001 May;107(5):1024-8.

Spiegelhalder et al. Influence of dietary nitrate on nitrite content of human saliva: Possible relevance to in vivo formation of N-nitroso compounds. Food Cosmet Toxicol. 1976 Dec;14(6):545-8.

Swann et al. Nitrosamine-induced carcinogenesis. The alklylation of nucleic acids of the rat by N-methyl-N-nitrosourea, dimethylnitrosamine, dimethyl sulphate and methyl methanesulphonate. Biochem J. 1968 Nov;110(1):39-47.

van Velzen et al. Relative significance of dietary sources of nitrate and nitrite. Toxicol Lett. 2008 Oct 1;181(3):177-81. Epub 2008 Aug 3.

White, J. Relative significance of dietary sources of nitrate and nitrite. J Agric Food Chem. 1975 Sep-Oct;23(5):886-91.

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