An increased intake of folate may reduce the risk of stroke by 20 per cent for male smokers, suggests a new study.
Over 26,000 male Finnish smokers took part in the study, which also indicated that other B-vitamins did not exert any beneficial effects on stroke risk in this population.
While the best health advice to smokers is clearly to give up smoking, the new study published online in the American Journal of Epidemiology suggests that an increased intake of folate may protect smokers from stroke.
Researchers from the Karolinska Institutet (Stockholm), the Finnish National Public Health Institute (Helsinki), and the National Cancer Institute, US National Institutes of Health (NIH) used data from the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study concerning 26,556 male smokers aged from 50 to 69.
Dietary intakes were assessed using a validated food frequency questionnaire and intakes of folate, vitamins B6 and B12, and methionine from the diet were calculated.
During 13.6 years of follow-up, the researchers documented 3,281 cases of stroke, including cerebral infarctions, intracerebral hemorrhages, and subarachnoid hemorrhages.
Lead author Susanna Larsson reports that men with the highest average intakes (410 micrograms per day) of folate were 20 per cent less likely to suffer a cerebral infarction than men with the lowest folate intakes (262 micrograms per day), after adjusting for age and other cardiovascular risk factors.
"An inverse association between folate intake and risk of stroke is biologically plausible because folic acid supplementation lowers blood homocysteine, which in high concentrations may cause vascular damage (endothelial dysfunction, increased arterial intimal-medial thickness, and increased arterial stiffness) and increased procoagulant activity," wrote Larsson.
"Meta-analyses have estimated that a 3-micromoles per litre decrease in blood homocysteine concentrations is associated with a 19-24 percent lower risk of stroke."
However, intakes of vitamins B6 and B12, and methionine were not associated with any type of stroke, added Larsson and co-workers.
"Although these observational data do not prove a causal relation, they indicate that high consumption of folate-rich foods (e.g., whole grains, green leafy vegetables, oranges, and legumes) may play a role in the prevention of stroke," concluded the researchers.
One in three Europeans are smokers, while the US figure is one in five. Tobacco smoke contains over 4,000 compounds, of which 60 are known carcinogens. The oxidative stress levels of smokers are significantly greater than non-smokers, and as such there is a bigger drain on the levels of antioxidants in the body.
Support for folic acid fortification
The number of deaths from stroke in North America has reportedly dropped by five per cent since the introduction of folic acid fortification, while figures in the non-fortifying UK have not changed, according to researchers from the US Centers for Disease Control and Prevention (CDC).
Mandatory fortification of certain food with folic acid was introduced in the US and Canada in 1998 with the primary outcome designed to be a reduction of birth defects. The programme has been successful in cutting the number of children born with neural tube defects by over 25 per cent.
Europe, on the other hand, has been dragging its feet on the issue of fortification, although a recent meeting between the Food Standards Association (FSA) and industrial lobby groups indicated that fortification could be soon be made compulsory.
By comparing stroke mortality rates in the United States and Canada for 1990 to 1997, and 1998 to 2002, with stroke mortality rates in England and Wales, the CDC researchers showed that between 1990 and 1997, the rate of death from strokes was already in decline in the US (0.3 per cent).
After introduction of the mandatory fortification program, the rate of death from strokes decreased significantly to 2.9 per cent.
In Canada, the fall in stroke mortality was even more pronounced, with an average decrease of one per cent for the period 1990 to 1997, and 5.4 per cent for 1998 to 2002.
Source: American Journal of Epidemiology
Published online ahead of print 12 February 2008, doi: 10.1093/aje/kwm395
"Folate, Vitamin B6, Vitamin B12, and Methionine Intakes and Risk of Stroke Subtypes in Male Smokers"
Authors: S.C. Larsson, S. Mannisto, M.J. Virtanen, J. Kontto, D. Albanes, J. Virtamo