What? Study X reports Nutrient Y does/does not Affect Condition Z
You may have seen the news questioning the brain benefits of omega-3s. Let’s discuss the Bad and Ugly points raised regarding omega-3 fatty acids (EPA and DHA) by Dr David Samadi.
Bad – While Ammann and colleagues did not find an association between red blood cell (RBC) levels of DHA and EPA with age-associated cognitive decline in older, dementia-free women, a single secondary analysis of a sub-study with observational data does not reflect the body of evidence. The Women’s Health Initiative Study of Cognitive Aging (WHICSCA) was ancillary to the primary randomized controlled trial (RCT) designed to assess the effect of postmenopausal homone therapy on age-related changes in cognitive function. In fact, hormone therapy negatively affected cognitive decline (doubling the risk of dementia) over 4 years but Amman et al do not factor this salient point into their findings. Moreover, years passed between the determination of RBC and cognitive measures. There are numerous other human studies reporting inverse correlations between DHA blood levels and risk of dementia and/or cognitive decline (see citations below) . Finally, with regards to claims based on animal and in vitro studies, Dr Samadi should follow FDA guidelines “these studies do not provide information from which scientific conclusions can be drawn regarding a relationship between the substances and disease in humans.”
Ugly – Dr Samadi continues on to mention a 70% increased risk in high-grade prostate cancer with omega-3 fatty acid supplementation based on a July publication (Brasky et al, 2013). TalkingNutrition.dsm.com has commented on this study previously. Again, Brasky et al conducted a secondary analysis of a subset of men participating in a RCT which did not supplement with omega-3 fatty acids, nor did they adjust for background PSA levels in their statistical analysis. The omega-3 conclusions with respect to prostate cancer risk in the SELECT trial were overblown.
Dr Samada does endorse the American Heart Association recommendation, based on evidence from prospective secondary studies, that 0.5 to 1.8g EPA + DHA supplementation (either as fatty fish or supplements) helps support cardiovascular health. Observational studies continue to show a positive effect of higher omega-3 fatty acid intakes on brain functions.
It isn’t transparent or in the best interest of the public to build news stories on rat studies. Keep following TalkingNutrition.dsm.com to help gain perspective on headlines such as “new study X finds that ingredient X does/does not affect organ/tissue/function Z”.
Ammann EM, Pottala JV, Harris WS, Espeland MA, Wallace R, Denburg NL, Carnahan RM, Robinson JG. Omega-3 fatty acids and domain-specific cognitive aging. 2013 Neurol doi:10.1212/WNL.0b013e3182a9584c
Shumaker SA, Legault C, Rapp SR, Thal L, Wallace RB, Ockene JK, Hendrix SL, Jones III BN, Assaf AR, Jackson RD, Kotchen JM, Wassertheil-Smoller S, Wactawaski-Wende J. Estrogen plus progestin and the incidence of dementia and mild cognitive impairment in postmenopausal women: The Women’s health Initiative Memory Study: A randomized controlled trial. 2003 JAMA doi:10.1001/jama.289.20.2651
Tan ZS, Harris WS, Beiser AS, Au R, Himali JJ, Debette S, Pikula A, DeCarli C, Wolf PA, Vasan RS, Robins SJ, Seshadri S. Red blood cell omega-3 fatty acid levels and markers of accelerated brain aging. 2012 Neurol doi:10.1212/WNL.0b013e318249f6a9
Phillips MA, Childs CE, Calder P, Rogers PJ. Lower omega-3 fatty acid intake and status are associated with poorer cognition function in older age : A comparison of individuals with and without cognitive impairment and Alzheimer’s disease. 2012 Nutr Neurosci doi:10.1179/1476830512Y.0000000026
Johnson E, Mcdonald K, Caldarella SM, Chung H-Y, Troen A, Snodderly DM. Cognitive findings of an exploratory trial of docosahexaenoic acid and lutein supplementation in older women. 2008 Nutr Neurosci doi:10.1179/147683008X301450
Guidance for industry: Evidence-based review system for the scientific evaluation of health claims – Final. Jan 2009. US Dept Health & Human Services, Food and Drug Administration.
Theodore M. Brasky, Amy K. Darke, Xiaoling Song, Catherine M. Tangen, Phyllis J. Goodman, Ian M. Thompson, Frank L. Meyskens, Jr, Gary E. Goodman, Lori M. Minasian, Howard L. Parnes, Eric A. Klein, and Alan R. Kristal. Plasma Phospholipid Fatty Acids and Prostate Cancer Risk in the SELECT Trial. 203 J Natl Cancer doi:10.1093/jnci/djt174