Association between fish consumption, long chain omega 3 fatty acids, and risk of cerebrovascular disease: systematic review and meta-analysis

BMJ 2012; 345 doi: (Published 30 October 2012)
Cite this as: BMJ 2012;345:e6698

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In their fascinating meta-analysis article Chowdhury, et al. (2012) found that fish consumption was “…moderately but significantly associated with a reduced risk of incident cerebrovascular disease…” but not so with omega 3 supplement use. (1) This brings to mind some questions. Could current fish consumption reflect early-life dietary patterns? Could current fish consumption reflect maternal and family food habits? Thus could fish consumption reflect lifetime omega 3 intake patterns whereas omega 3 supplements reflect short-time bents? If so how might this be significant?

Although there may be lifelong shaping of the epigenome, early life influences on the epigenome could be highly important because they can put the individual on a disease trajectory. (2,3) It has been asserted that epigenetics, such as hypomethylation of DNA, plays a role in vascular disease and stroke risk. (4,5) Using an animal model, Kulkarni, et al. (2011) found that the omega 3 fatty acid DHA promotes healthy global DNA methylation in the placenta. (6) Could DHA also have a role in shaping the epigenome in such a way as to influence cerebrovascular disease risk later in life? Could this be one of the mechanisms by which fish consumption promotes cerebrovascular health? Could omega 3 fatty acids promote health in part through an epigenetic mechanism? What impact might omega 3 fatty acids have on the epigenome at different points in the lifecycle?

1. Chowdhury R, Stevens S, Gorman D, Pan A, Warnakula S, Chowdhury S, Ward H, Johnson L, Crowe F, Hu FB, Franco OH Association between fish consumption, long chain omega 3 fatty acids, and risk of cerebrovascular disease: systematic review and meta-analysis. BMJ. 2012 Oct 30;345:e6698.
2. Szyf M The early-life social environment and DNA methylation. Clin Genet. 2012 Apr;81(4):341-9.
3. Attig L, Gabory A, Junien C. Nutritional developmental epigenomics: immediate and long-lasting effects. Proc Nutr Soc. 2010 May;69(2):221-31.
4. Turunen MP, Aavik E, Ylä-Herttuala S Epigenetics and atherosclerosis. Biochim Biophys Acta. 2009 Sep;1790(9):886-91.
5. Baccarelli A, Wright R, Bollati V, Litonjua A, Zanobetti A, Tarantini L, Sparrow D, Vokonas P, Schwartz J Ischemic heart disease and stroke in relation to blood DNA methylation. Epidemiology. 2010 Nov;21(6):819-28.
6. Kulkarni A, Dangat K, Kale A, Sable P, Chavan-Gautam P, Joshi S. Effects of altered maternal folic acid, vitamin B12 and docosahexaenoic acid on placental global DNA methylation patterns in Wistar rats. PLoS One. 2011 Mar 10;6(3):e17706.

Competing interests: None declared

Celia M Ross, Activities Assistant

Franciscan Care Center, Hockessin, Delaware, USA

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It is widely acknowledged that omega 3 essential fatty acid (EFA) plays a vital role in homeostatic functions within the human body, notably the eicossanoid balance. Omega 3 (balanced with the correct ratio of omega 6) is essential, particularly in fertility and reproduction, breast feeding and child development including healthy brain development. Attention to good nutrition at an early stage of life may be a good starting ground for future prevention of problems – including cerebrovascular disease amongst many others.

Conflicting commercial interests have long decided our food choices, particularly fats. Processed foods are admonished as being an unhealthy choice, yet processed fats such as polyunsaturated cooking oils, low-fat spreads and margarine with their suggested omega 3 content are heart friendly – really? Commercial food processing destroys a significant amount of EFAs, along with their oxygenating ability. Consumption of good quality omega 6 and 3 EFAs is a haphazard affair. Polyunsaturated oils are unstable and very quickly become rancid. Oxidized fatty acids are dangerous to our health. Lipid peroxidation and oxidative stress are important factors in this damage. (1) Further damage is also caused by heating polyunsaturated fats in cooking (particularly frying foods).

A high fruit and vegetable consumption has a favourable effect on plasma antioxidant concentrations. (2) However, vitamin content of food is variable with age, conditions of storage and cooking methods. Modern farming methods and soil depletion have also left many foods nutritionally barren.

If we choose to take omega 3 supplements they need to be very carefully sourced. Supplements are often seen on display in the full sun in the chemist/health food shop window, or may be languishing in the back of a cupboard at home awaiting a thought to improve our health - again rancidity is a problem.

As Chowdhury et al (3) suggest, whole fish is the nutritious answer to the consumption of Omega 3. One thing is for certain a fish will always let you know when it is off! As a priority we need to be sure of our ecological responsibilities towards sustainability and prevention of pollution to fish. We also need to ensure that the population can access correct information on consuming essential fatty acids, both in the diet and by supplementation.

(1) Moore, K., and L. J. Roberts 2nd. 1998. Measurement of lipid peroxidation. Free Radic. Res. 28: 659–671.
(2) John J et al (2002) Effects of fruit and vegetable consumption on plasma antioxidant concentrations and blood pressure: a randomised controlled trial Lancet 2002; 359: 1969-1974
(3) Association between fish consumption, long chain omega 3 fatty acids, and risk of cerebrovascular disease: systematic review and meta-analysis BMJ 2012;345:e6698 Rajiv Chowdhury, Sarah Stevens, Donal Gorman, An Pan, Samantha Warnakula, Susmita Chowdhury, Heather Ward,Laura Johnson, Francesca Crowe, Frank B Hu, Oscar H Franco.

Competing interests: None declared

Jane E Collis, Independent Researcher

independent, Penrhyn Close, Kenilworth Warks UK

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The present editorial brings out the fact that long chain omega 3 fatty acids following fish consumption as the dietary source provides minimal or rather non-significant protection against cerebrovascular events. The concept of eating the whole food instead of the food supplement is to be encouraged. The package in which the essential nutrients is present plays a more important role than just mere supplementation of isolated ingredients. The additive or synergistic effects of total nutrients present in a dietary source is more significant than the individual ones.

The beneficial effects of fish consumption and the omega 3 fatty acids are proven for cardiovascular health. It could be that the effects of these nutrients are more pronounced in cardiovascular system than the cerebrovascular system. The blood-brain barrier does not allow fatty acids to reach brain tissue possibly to extract the maximum benefit from such dietary sources. Balanced nutrition is the best method to get maximum beneficial effects from the nutrients. The nature's mixture of ingredients possibly in the right proportion in our diet may be more important than picking and choosing individual nutrients to stake claim as the nutrient of choice for health.

Competing interests: None declared

dhastagir s Sheriff, Professor

Faculty of Medicine, Benghazi University, Benghazi, Libya

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