Abstract
- Background
Micronutrient status can affect cognitive function at all ages. Vitamin deficiencies could influence memory function and might contribute to age-associated cognitive impairment and dementia. Vitamin $\text{B}_6$, comprising three chemically distinct compounds (pyridoxal, pyridoxamine, and pyridoxine), is involved in the regulation of mental function and mood. Vitamin $\text{B}_6$ is also an essential homocysteine remethylation cofactor, and deficiency is associated with an increase in blood homocysteine levels—a risk factor for cerebrovascular disease and direct neurotoxicity. Neuropsychiatric disorders including seizures, migraine, chronic pain, and depression have been linked to vitamin $\text{B}_6$ deficiency, which is common among older people.
- Objectives
To assess the efficacy of vitamin $\text{B}_6$ supplementation in reducing the risk of developing cognitive impairment in older healthy people, or improving cognitive functioning in people with cognitive decline and dementia, whether or not vitamin $\text{B}_6$ deficiency has been diagnosed.
- Methods
The Specialized Register of the Cochrane Dementia and Cognitive Improvement Group (CDCIG), The Cochrane Library, MEDLINE, EMBASE, PsycINFO, CINAHL, and LILACS were searched on 16 March 2008. Unconfounded, double-blind randomized controlled trials (RCTs) comparing vitamin $\text{B}_6$ with placebo in healthy older people or people with cognitive decline or dementia were included. The primary outcome was efficacy on cognitive function. Two reviewers independently evaluated studies and extracted data. Weighted mean differences (WMD) with $95\%$ confidence intervals ($\text{CI}$) were calculated.
- Results
No trials of vitamin $\text{B}_6$ involving people with cognitive impairment or dementia were found. Two trials (Bryan 2002; Deijen 1992) involving 109 healthy older participants were included. In Bryan 2002, 12 healthy older women ($65\text{--}92\text{ years}$) received $75\text{ mg/day}$ oral vitamin $\text{B}_6$ for 5 weeks compared with 21 receiving placebo; no statistically significant benefits on mood or cognition were observed. In Deijen 1992, 76 healthy older men ($70\text{--}79\text{ years}$) received $20\text{ mg/day}$ pyridoxine hydrochloride or placebo for 12 weeks; no statistically significant differences in cognition or mood were found between groups. However, Deijen 1992 reported that supplementation significantly increased plasma pyridoxal-5'-phosphate ($\text{WMD} = 238$, $95\%\text{ CI} = 211.58\text{ to }264.42$, $p < 0.00001$) and erythrocyte aspartate aminotransferase activity ($\text{WMD} = 0.43$, $95\%\text{ CI} = 0.30\text{ to }0.56$, $p < 0.00001$). Neither trial measured homocysteine levels. No dropouts or adverse events were reported.
- Conclusions
This review found no evidence for short-term benefits of vitamin $\text{B}_6$ in improving mood or cognitive functions. Oral vitamin $\text{B}_6$ supplements improved biochemical indices of vitamin $\text{B}_6$ status in healthy older adults, but potential effects on blood homocysteine levels were not assessed. More randomized controlled trials are needed to explore possible benefits from vitamin $\text{B}_6$ supplementation in healthy older adults and individuals with cognitive impairment or dementia.
https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD004393/abstract