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Vitamin B = Lower Stroke Risk
Unlike other similar reports that failed to find a significant effect of vitamin B supplementation on stroke risk, an updated meta-analysis has shown that taking these vitamins to lower homocysteine levels significantly reduces the stroke rate.
Just to be clear, folate (vitamin B9) and vitamin B12 are important regulators of homocysteine metabolism. In several jurisdictions, cereals are fortified with folate. Folic acid is a supplemental form of folate.
Several biological factors may affect whether vitamin B supplements will affect stroke risk, the study showed.
“Based on our results, the ability of vitamin B to reduce stroke risk may be influenced by a number of other factors, such as the body's absorption rate, the amount of folic acid or vitamin B12 concentration in the blood, and whether a person has kidney disease or high blood pressure,” said Yuming Xu, MD, Department of Neurology, The First Affiliated Hospital of Zhengzhou University, China, in a press release.
The study is published online September 18 in Neurology.
Researchers searched for randomized controlled trials published before August 2012 that compared vitamin B supplementation with placebo, very-low-dose B vitamins, or usual care; had a minimum follow-up of 6 months; and included stroke events as a study endpoint.
Since 2010, several important meta-analyses have been published on the effects of therapy to lower homocysteine levels with B vitamin supplementation on vascular disease risk. The new meta-analysis included studies that were omitted from previous reports and adopted stricter inclusion criteria (it excluded several studies because of small samples, zero rates of outcome events, ill-defined endpoints events, and inappropriate control group design).
As for analyses specific to vitamin B12, the report did not find a significant benefit for reduction of stroke events in subgroups according to intervention dose, reduction of homocysteine level, or baseline blood vitamin B12 concentration. An analysis of populations with folate fortification of cereal products also failed to obtain significant results regarding B12 dose. Other research had reported that 1 mg of B12 is beneficial.
“Our clinical implication is that metabolic B12 deficiency should be more thoroughly followed and treated, so that such deficiencies are found and treated appropriately with B vitamin intervention,” the authors write. “In future, we should consider adoption of specific administration routes rather than a single oral route, e.g. oral route in populations with inadequate dietary intake or injection route in populations with B12 malabsorption to obtain effective intervention results.”
As for baseline blood pressure levels, the meta-analysis identified a benefit of B vitamins in study participants with baseline high blood pressure. Hyperhomocysteinemia is known to promote hypertension. In China, guidelines for hypertension recommend reducing homocysteine levels to manage blood pressure.
The addition of some new studies since the last meta-analysis explains the different findings, said Dr. Sacco, adding that the change is not sufficient to alter current guidelines.
“When one examines the largest clinical trials individually, there is no significant effect of vitamin B supplementation for primary or secondary stroke prevention, so it's difficult to use a meta-analysis to change evidence-based guidelines. There may be some subgroups of patients who could benefit from vitamin B supplementation, but unfortunately the effects are small and limited.”
Abstract
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