The scientific evidence is strong enough to justify using folic acid as a cheap and simple way of reducing heart disease and strokes, say researchers in this week's BMJ.
Debate continues over whether raised homocysteine levels in the blood (an amino acid implicated in the development of arterial disease) causes heart disease and stroke, and whether folic acid, which lowers homocysteine, will help reduce the risk of these disorders.
So heart expert, Dr David Wald and colleagues set out to clarify the issue. They examined all the evidence from different studies to see whether raised homocysteine is a cause of cardiovascular disease.
Some studies looked at homocysteine and the occurrence of heart attacks and strokes in large numbers of people (cohort studies), some focused on people with a common genetic variant which increases homocysteine levels to a small extent (genetic studies), while others tested the effects of lowering homocysteine levels (randomised controlled trials).
The cohort studies and genetic studies yielded similar results, indicating a protective effect from lower homocysteine levels, even though they did not share the same sources of possible error. The randomised trials were too small to be conclusive although their results were consistent with the expected protective effects of folic acid.
The conclusion that homocysteine is a cause of cardiovascular disease explains the observations from all the different types of study, even if the results from one type of study are, on their own, insufficient to reach that conclusion, say the authors.
Since folic acid reduces homocysteine concentrations, it follows that increasing folic acid consumption will reduce the risk of heart attack and stroke.
They therefore take the view that the evidence is now sufficient to justify action on lowering homocysteine concentrations, although the position should be reviewed as evidence from ongoing clinical trials emerges.
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