Historical study links fish to stroke
wealth of scientific studies, but data from a historical cohort
study has led to a surprising observation - that high fish intake
in childhood may be linked to eventual death from stroke.
Omega-3 fatty acid, one of the best sources of which is oily fish, are believed to promote better cognitive function in both children and adults, and some research has pointed to improved behavior of children with ADHD when their diet was supplemented with omega-3.
Fish consumption has also been connected to long- and short- term heart health, joint health, and may also help protect against protect against some forms of cancer.
The startling new observations were made by researchers at the University of Bristol in the UK, who examined dietary taken from a survey known as Boyd Orr that was carried out across 16 centers in England and Scotland between 1937 and 1939. It was followed up using the register of the National Health Service.
The researchers looked at consumption of fruit, vegetables, fish, oily fish, total fat, saturated fat, carotene, vitamin C and vitamin E by 4,028 children aged between 0 and 19 years, estimating intake from total household dietary intake.
They sought to find out whether there was any correlation between consumption of these foods and nutrients in childhood and cause of death in adulthood - in particular death attributed to coronary heart disease and stroke.
Their results were published in the journal Heart (2005; 91: 894-898). As would be expected, higher intake of vegetables was associated with lower risk of stroke. But the correlation between a higher intake of fish and a higher risk of stroke in later life was altogether more surprising.
As a historical cohort study, the research does not seek to explain the cause of the findings, as a clinical study would. Given the wealth of scientific evidence in favor of eating fish as part of a balanced, healthy diet, the new study may not be cause for concern, but further investigation may well be warranted.
Indeed, the researchers were cautious in the conclusions they drew, that: "aspects of childhood diet, but not antioxidant intake, may affect adult cardiovascular risk."
Although they conceded that the number of diet-disease associations examined may mean the observations were due to chance, and the fact that the original data was based on household rather than individual intake could have led to some inaccuracies, this is not the first time the fish-stroke connection has been made.
The authors cite two studies of temporal trends in fish consumption and stroke in the UK and Japan (Medical Hypotheses 1990; 31: 135-9 and Preventative Medicine 1983; 12:222-7), which fit with the observations of the new study. Another, in the Lancet (2001; 358:50), suggested that fish intake in early life may have an effect on membrane concentrations of arachidonic acid, thereby influencing risk of stroke, particularly haemorrhagic stroke.
A spokesperson for Seafish in the UK told NutraIngredients.com: "There are thousands of other scientific studies which testify the health benefits of seafood, so we would continue to support the official government recommendations from the Food Standards Agency that we should actually be increasing the amount of seafood in the diet."
The UK's Food Standards Agency recommends that people eat at least two portions of fish a week, one of which should be oily fish. It says that, at present, most people do not eat enough fish.
However because of the low levels of contaminants in oily fish that can build up in the body, girls, pregnant or breastfeeding women and women who might one day have a baby are advised to eat no more than two portions of oily fish a week. For men and other women the maximum is four portions.
It is also advised that children should avoid eating any shark, swordfish or marlin, because the mercury levels in these fish can affect the development of their nervous systems.