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Vitamin Supplementatin and its Effects On Cognitive Function
Researchers have found no correlation between vitamin B supplementation and improved cognitive function, according to a meta-analysis in the January 8 Archives of Internal Medicine.
The literature review, conducted by researchers from Tufts–New England Medical Center Evidence-based Practice Center in Boston, sought to explore whether increased serum levels of B vitamin supplements improved cognitive function, as research has revealed that low vitamin B and folic acid levels, when coupled with high homocysteine levels, might correlate with decreased performance on cognitive tests. The review tied in to a larger report on the association between B vitamins, berries, and neurocognitive function.
The researchers conducted a literature search for randomized trials and systematic reviews of B vitamins in MEDLINE and Commonwealth Agricultural Bureau Abstracts. Additional studies were sought from neurology and vitamin research experts and from reference lists of selected articles, including review articles and meta-analyses. To qualify, a trial had to document the type of vitamin, dose, and route of administration, as well as specify outcomes related to the diagnosis or severity of Alzheimer’s disease, other age-related neurocognitive disorders, cognitive impairment, or tests of cognitive function.
Included in the final analysis were 14 trials that involved testing folic acid supplementation and vitamins B6 and B12 with cognitive function outcomes. The studies drew upon 50 different cognitive function tests that evaluated each participant’s word-learning abilities, executive function, word fluency, sensorimotor speed, and memory.
Data that were evaluated included the mean baseline serum levels in both intervention and control arms, within-cohort changes, and the net change of the outcome. According to the authors, three trials of vitamin B6 and six of vitamin B12, in a variety of doses, routes of administration, and populations, found no effect on cognitive function.
TAKING THEIR VITAMINS
The vitamin B6 trials included 19 to 88 participants, each of whom were taking doses that ranged from 12 to 75 mg/day for five or 12 weeks. Across studies, nine different cognitive function subtests were used, and no statistical difference was reported, except on one test, where there was a significant improvement in long-term memory with vitamin B6 compared with placebo.
The vitamin B12 trials included 18 to 70 participants. Two of the six trials recruited cognitively intact participants with normal or low vitamin B12 levels, while one trial included participants with cognitive impairment and one included participants with a range of cognitive function. In each trial, there were different doses and administration routes, ranging from 0.01 mg/day to 1 mg/week intramuscularly. Three trials included oral vitamin B12. In all of the trials, duration of supplementation ranged from four weeks to six months.
On most of the tests performed, there was no improvement in cognitive function, and only three of 35 cognitive subtests showed any statistically significant difference between participants receiving vitamin B12 and those taking placebo. In fact, statistically significant net worsening on cognitive functioning tests was found in two tests. However, in one of those tests, the outcome was driven by a statistically significant improvement in the placebo arm that was not seen in the treatment arm.
Of the folic acid trials, only one of three found a benefit in cognitive function in people with cognitive impairment and low baseline serum folate levels. The trials included a total of 39 participants. Two trials were conducted among participants with dementia or cognitive impairment, and one among participants with normal cognitive function. The trials lasted five to 10 weeks and tested various doses of folic acid, ranging from 0.75 to 20 mg/day. Overall, five tests found a net improvement and three found a net worsening of cognitive function. In the third trial of cognitively impaired participants with low baseline folate serum levels, 15 mg/day of folic acid supplementation resulted in a net benefit on all six cognitive tests used; improvement on four of these tests was statistically significant. The results lead the authors to believe that cognitive improvement after folic acid intervention was correlated with a low level of folate at baseline. However, the authors cautioned, given the paucity of evidence, any conclusions remain tentative.
BIG DOSES, LITTLE EFFECTS
Six trials found that combinations of the B vitamins had no effect on cognitive function. In fact, among three trials, placebo recipients had greater improvements in a small number of cognitive tests.
Despite the wide battery of tests reviewed by the authors, they noted that the quality of the studies examined was often compromised by several factors, including incomplete reporting of methodology and results, lack of blinding, small sample size, short duration, and other limitations
—Tara Hayden
Suggested Reading
Balk EM, Raman G, Tatsioni A, et al. Vitamin B6, B12, and folic acid supplementation and cognitive function: a systematic review of randomized trials. Arch Intern Med. 2007;167:21-30.
Balk E, Chung M, Raman G, et al. B Vitamins and Berries and Age-Related Neurodegenerative Disorders: Evidence Report/Technology Assessment No. 134. Rockville, MD: Agency for Healthcare Research and Quality; April 2006.
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