For twenty years, I have heard that eating "oily fish" is good for you. Suddenly, its health benefits appear less certain. Four years ago, I attended the EUROFEDA conference in Cambridge on antioxidants (held at Churchill Hall; a college devoted to science and technology, and named in honour of Winston Churchill, who believed that it was new technology that would help to win the war, and then rebuild and advance the nation). The concluding remark of the chairman of this conference was that the term "antioxidants" should be reversed to the older "micronutrients", in accord with the concluding affirmation that even after forty years research, we know little about the dietary molecular properties of these materials but that on epidemiological grounds - e.g. the "Mediterranean diet" - they are "good for you". However, having been invited to lecture in Greece a few years back, I was thoroughly struck by the apparent level of contentment among the people I met and I wonder whether it is so much the diet and more so the less stressed prevailing human mental state in the Mediterranean countries which furnishes the greater health benefits.
Also according to epidemiological studies (medical statistics), Green Tea is believed to protect against both breast and prostate cancer; however, there is recent evidence that the role of the majorly effective polyphenolic compound EGCG is not that of a free radical scavenger (antioxidant) but that its cluster of OH groups enable it to bind to the cell surface and presumably alter the cell signaling mechanism in such a way that a cancer is avoided. Thus, while many "antioxidants" undoubtedly can intercept free radicals and ameliorate their influence in damaging proteins and DNA, their molecular complexity lends to them a further role at the level of molecular biology which is sufficient to prevent the progression from a simple molecular lesion to a cancer. Hence the word "micronutrient" may prove more global than "antioxidant". We have recently published a review (Chemico-Biological Interactions, 160 (2006) pages 1-40) of the role of free radicals, metals and antioxidants in the development and prevention of cancer.
So, what about the "oily fish"? Are they good or bad for you? A major review has been published by researchers at the University of East Anglia (UEA) on the subject, the balance of which suggests that oily fish are not necessarily all they have been cracked up to be. The topic was overviewed by The Independent recently (Friday 24 March). Sales of fish oil capsules provide a thriving industry, aimed at those who wish to obtain the health benefits, but can't stand the taste of the fish themselves. Interestingly, a study called DART-2 published in 2003 changed the overall view, since it concluded that in a study of over 3,000 men, there was a higher death rate from heart disease in those taking fish oil capsules. This reminds me, in fact, of a similar study named CARET (published in 1999? from memory), which aimed to investigate the anti-cancer properties of beta-carotene. The project was stopped after only nine months when a 20% increase in cancer rates was discovered among those taking the supplement compared with the control (i.e. those who weren't on it).
However, the UAE review, which includes 89 different studies of omega 3 fats (the key ingredient in fish oils) found no clear evidence that they are of any benefit at all in protecting against heart disease, strokes or cancer. The British Heart Foundation has speculated that these finding might be linked to mercury levels in fish, which was a suggestion made by the UEA authors. Mercury is highly toxic and accumulates in oily fish which live in waters contaminated with the metal and its compounds. There was a notable and extreme case which occurred in Japan in the early 1950's at the seaside fishing village of Minamata, on Kyusha Island, where the cats went mad from eating fish contaminated by dimethylmercury, a potent neurotoxin formed by biological methylation of mercury compounds which had been dumped into the sea water by industry. Humans too sustained considerable health problems, including death.
We are of course not speaking of anything on the scale of Minamata, but organomercury compounds like dimethylmercury may well show toxic effects, even at relatively low levels, and it is the general consensus that more research is needed on fish oils (and oily fish themselves, I presume, not just the synthetic oils in isolation?) to resolve the whole matter.
I shall await the results of this with a lively interest, but meanwhile try to even out the odds by eating a reasonably balanced diet!