Fish Oil And Health

I wanted to follow up last week’s post on DHA supplementation with a look into the research on fish oil supplementation, since while fish oil is a common source of supplemental DHA, there are supplements that contain pure DHA (as opposed to the normal mix of fats present in fish oil). While I concluded that there isn’t scientific research to support supplementing with pure DHA, there’s a fair amount of work that supports fish oil supplementation.

Certain benefits associated with fish oil supplementation begin during pregnancy. Thorsdottir (ok, sorry for the commentary, but that is a REALLY cool name when you say it out loud!) and colleagues found that Icelandic women who consumed the lowest quantities of fatty fish had smaller babies than those who consumed larger quantities of fish. Interestingly enough, however, those who consumed the most fish (containing more than a tablespoon of fish oil daily) also had shorter babies with smaller head circumferences. These women were getting three times the recommended daily vitamin A, and twice the recommended vitamin D as a result of their very high fish intake, which the researchers speculated might have had something to do with the results (both vitamins A and D are toxic in excessive quantities). Thorsdottir and colleagues recommended moderate fish and/or fish oil consumption during pregnancy (though “moderate” to an Icelandic research team is probably not the same as “moderate” to an American, given dietary norms). Olsen and colleagues found that moderate fish oil supplementation helped prevent pre-term delivery of a singleton baby in a high-risk (earlier pre-term delivery) mother, though the fish oil didn’t prevent pre-term delivery of twins. The researchers noticed no negative effects of fish oil on either mother or infant. Fish oil supplements during pregnancy appear to extend their effects into the first six months of lactation (Dunstan et al, 2007). Polyunsaturated fatty acids (PUFAs) from fish oil clearly pass into breast milk The key PUFAs are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which typically represent a large fraction of the total fish oil in a supplement capsule. In the Dunstan study, women who took fish oil during pregnancy (but not continuing into lactation) had higher levels of DHA in breast milk at three days, six weeks, and six months postpartum. The differences between the women who were supplemented and those who were not supplemented disappeared after six months postpartum. Infants of women with higher PUFA levels in breast milk had higher PUFA status themselves, and scored higher on a variety of developmental tests (both physical and cognitive) at 2.5 years. On the other hand, a very large study by Makrides et al failed to find much benefit associated with fish oil supplementation during pregnancy; women taking fish oil did not have lower rates of postpartum depression, nor did their infants score better on developmental assessments. A commentary on that same study (Oken et al) points out that some of the observational studies suggesting PUFA intake benefits (such as the Icelandic study by Thorsdottir) are based upon intake of whole fish, rather than fish oil supplements. Whole fish could contain more biologically active PUFAs, minerals that affect PUFA action, or other unidentified compounds. Oken and colleagues also note that the Makrides study tested infant development, while other fish oil studies tested toddlers and preschoolers. They point out that tests might not be sensitive enough to detect differences in infant development, and that differences might not become apparent until the babies were older. A further commentary on the Makrides study (Suzuki) points out that there were some differences in postpartum depression levels between women supplemented with fish oil and those receiving a placebo, but that the depression score cutoff value that Makrides et al chose did not allow for detection of those differences. Suzuki suggests that fish oil supplementation may play a role in reducing cases of subclinical (or less easily detected) depression.

Continued fish oil supplementation during lactation also appears to have benefits. Supplementation appears to increase levels of IgA (a type of antibody passed from mother to baby through breast milk) (Dunstan et al, 2004). There’s also evidence that it helps to reduce the risk of allergies (see, for instance, Dunstan et al 2003, Furuhjelm et al). Direct supplementation of infants may also confer benefits; a study by Damsgaard and colleagues noted that infants supplemented with fish oil had healthier blood lipid (fat) profiles at a year of age. Since blood lipid profile is a marker for heart disease risk, this is a potentially important finding.

Developmental benefits aside, fish oil supplements have also been associated with a reduction in several inflammatory disease processes, including rheumatoid arthritis (Kremer et al), asthma (Nagakura et al), ulcerative colitis (Hawthorne et al), and cardiovascular disease (see, for instance, Nestel et al, Geleijnse et al). Many of the studies on the benefits of fish oil refer to doses in the neighborhood of 3-4 grams of fish oil (containing 1-2 grams each of EPA and DHA) a day, with the caveats that while some fish oil is better than none, higher dosages show diminishing returns (and possibly harm).

It’s worth noting that while the benefits above are all conferred by DHA-containing fish oil capsules (and while many of the benefits are directly linked to the DHA in those capsules), supplementation with fish oil isn’t the same as supplementation with pure DHA. This is because fish oil is a blend of many different fats, of which DHA and EPA are only two. Research has shown repeatedly that separating out, purifying, and supplementing with a single compound suspected to be the “active” agent in a healthful food can have unintended (and sometimes detrimental) consequences. This is, for instance, what Miller and colleagues found in their work on vitamin E, which had previously (Knekt et al) been touted as having heart disease-reducing properties. In the case of vitamin E, it’s likely that by separating out a single form (alpha-tocopherol) of a vitamin that occurs in nature as a mixture of several forms, the supplemental vitamin E could be sending an unintended biological signal. Further support for the notion that there’s more to fish than DHA lies in the observation (Oken et al) that habitual fish-eaters note more predictable fish-related benefits than those taking fish oil supplements. With regard to supplements, there are two things to keep in mind: more is not better, and purifying the active ingredient isn’t necessarily an improvement over seeking out a source of that beneficial ingredient.


Science Bottom Line:* There is a multitude of evidence to support using fish oil (or better yet, eating fatty fish regularly!) if you’re…human. And especially if you’re a human who is pregnant, nursing, growing, and/or affected by an inflammatory disease process. No research suggests that moderate fish oil supplementation is harmful, and since fish oil is typically manufactured from small fish like anchovies, there’s absolutely minimal risk of mercury contamination in commercial capsules (meaning you don’t really need to seek out algae-based capsules, and probably shouldn’t, since the research is largely on fish, as opposed to algae, oil).


What has been your experience with fish oil?



Damsgaard et al. Fish oil affects blood pressure and the plasma lipid profile in healthy Danish infants. J Nutr. 2006 Jan;136(1):94-9.

Dunstan et al. Fish oil supplementation in pregnancy modifies neonatal allergen-specific immune responses and clinical outcomes in infants at high risk of atopy: a randomized, controlled trial. J Allergy Clin Immunol. 2003 Dec;112(6):1178-84.

Dunstan et al. The effect of supplementation with fish oil during pregnancy on breast milk immunoglobulin A, soluble CD14, cytokine levels and fatty acid composition. Clin Exp Allergy. 2004 Aug;34(8):1237-42.

Dunstan et al. The Effects of Fish Oil Supplementation in Pregnancy on Breast Milk Fatty Acid Composition Over the Course of Lactation: A Randomized Controlled Trial. Pediatr Res. 2007 Dec;62(6):689-94.

Furuhjelm et al. Fish oil supplementation in pregnancy and lactation may decrease the risk of infant allergy. Acta Paediatr. 2009 Sep;98(9):1461-7. Epub 2009 Jun 1.

Geleijnse et al. Blood pressure response to fish oil supplementation: metaregression analysis of randomized trials. J Hypertens. 2002 Aug;20(8):1493-9.

Hawthorne et al. Treatment of ulcerative colitis with fish oil supplementation: a prospective 12 month randomised controlled trial. Gut. 1992 Jul;33(7):922-8.

Knekt et al. Antioxidant vitamin intake and coronary mortality in a longitudinal population study. Am J Epidemiol. 1994 Jun 15;139(12):1180-9.

Kremer et al. Effects of high-dose fish oil on rheumatoid arthritis after stopping nonsteroidal antiinflammatory drugs. Clinical and immune correlates. Arthritis Rheum. 1995 Aug;38(8):1107-14.

Makrides et al. Effect of DHA Supplementation During Pregnancy on Maternal Depression and Neurodevelopment of Young Children: A Randomized Controlled Trial. JAMA. 2010 Oct 20;304(15):1675-83.

Miller et al. Meta-Analysis: High-Dosage Vitamin E Supplementation May Increase All-Cause Mortality. Ann Intern Med. 2005 Jan 4;142(1):37-46. Epub 2004 Nov 10.

Nagakura et al. Dietary supplementation with fish oil rich in omega-3 polyunsaturated fatty acids in children with bronchial asthma Eur Respir J. 2000 Nov;16(5):861-5.

Nestel et al. Fish oil and cardiovascular disease: lipids and arterial function. Am J Clin Nutr. 2000 Jan;71(1 Suppl):228S-31S.

Oken et al. Fish, Fish Oil, and Pregnancy. JAMA. 2010 Oct 20;304(15):1717-8.

Olsen et al. Randomised clinical trials of fish oil supplementation in high risk pregnancies. Fish Oil Trials In Pregnancy (FOTIP) Team. BJOG. 2000 Mar;107(3):382-95.

Suzuki T. Maternal Depression and Child Development After Prenatal DHA Supplementation — A Reply. JAMA. 2011 Jan 26;305(4):359-60; author reply 360-1.

Thorsdottir et al. Association of fish and fish liver oil intake in pregnancy with infant size at birth among women of normal weight before pregnancy in a fishing community. Am J Epidemiol. 2004 Sep 1;160(5):460-5.


3 Comments (+add yours?)

  1. Trackback: Do DHA Supplements Help Build Brains? |
  2. Arwyn
    Oct 25, 2011 @ 02:47:53

    My only comment is that kids might surprise you on the fish front: the Boychick has been happily chomping on plain old cod liver oil capsules since he was a year and a half old. Not only does he not mind the taste, apparently, he asks for them. (Which is how it started: he asked, I shrugged and gave him one, he ate it, and I tried to not let my eyebrows fly off into space.)


    • SquintMom
      Oct 25, 2011 @ 03:39:01

      Wow, good to know! I certainly have no problem letting her try the capsules!! Thanks for the advice. 🙂


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