Enthusiasm for taking vitamin D to promote brain health has taken a knock after 2 studies in the same population have found no association between vitamin D levels and cognition or cerebrovascular pathology.
The studies were both conducted in an older middle-aged healthy population who were participating in the Atherosclerosis Risk in Communities (ARIC) Brain MRI Study.
The cognition study, published online in the European Journal of Neurology on May 21, did not find significant associations between lower levels of 25(OH)D and lower cognitive test scores at baseline, change in scores over time, or dementia risk in 1650 individuals.
The MRI study, published online in JAMA Neurology on May 26, included 1622 individuals from the same population who underwent baseline brain MRI, 888 of whom had a second brain MRI examination 10 years later. Results showed that 25(OH)D levels were not associated with white matter hyperintensities or prevalent subclinical infarcts in cross-sectional or prospective analyses.
"Our results dampen the enthusiasm for vitamin D being a panacea for brain health. We are urging caution before everyone gets carried away with taking vitamin D, and we cannot recommend at this time that people take it to protect against cognitive decline," Erin Michos, MD, Johns Hopkins University School of Medicine, Baltimore, who was an author on both studies, commented to Medscape Medical News.
"It is not completely benign," she added. "It can cause side effects at high doses. It is not a good idea to take supplements if you don't need to."
Cause of Disease or Just a Marker?
She explained that low levels of vitamin D are believed by many to be a potential risk factor for cardiovascular and brain disease. Previous studies have shown associations between low levels of vitamin D and hypertension, diabetes, myocardial infarction, and stroke.
"If this is proved to be causal then vitamin D levels could be modified quite easily and the cause could be treated, but we don't know if it is causal or not," she added. "Although low vitamin D has been associated with poor outcomes, it may just be a marker of poor health. People in poor health are likely to spend less time outside so will consequently have lower levels of vitamin D. Our results provide some caution for the idea that vitamin D may be good for brain health because we couldn't even find an association."
Because low vitamin D has been associated hypertension and diabetes, which in turn have been associated with white matter hyperintensities and cognitive impairment, she noted, their hypothesis was that low levels of vitamin D would be associated with white matter hyperintensities, silent strokes, and cognitive impairment. "But we didn't find any relationship between vitamin D levels and any of these outcomes in any of our analyses."
Dr. Michos noted that there have been several studies on low vitamin D and cognition, many of which have shown a positive association.
"We could only find one other study that looked at brain pathology and that was positive, but it was cross-sectional — it just looked at vitamin D and brain pathology at one time point — and included an older population than our study. We did a cross-sectional analysis, but we also looked at changes over time and found no association in either analysis."
She also pointed out that the current studies included a younger and healthier population (average age, 62 years) than has been included in previous studies. "Maybe that is why we didn't find an association. It might be that elderly people have lower levels of vitamin D as they get less sunlight."
She added that before any clinical recommendations can be made, trials need to show reduced outcomes with vitamin D treatment. Some such studies are now underway. One is the National Institutes of Health–sponsored VITAL study looking at the incidence of stroke and myocardial infarction in older individuals randomly assigned to 2000 IU of vitamin D or placebo.
Eur J Neurol. Published online May 21, 2014. Abstract
JAMA Neurol. Published online May 26, 2014. Abstract
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Cite this: No Link Between Vitamin D and Cognition, Brain Pathology - Medscape - Jun 03, 2014.