By Hara Estroff Marano, published on January 1, 2011 - last reviewed on June 9, 2016
There are, in all, nine of them, and while all of the B vitamins play a role in metabolism, some also protect the nervous system. Vitamins B6 (pyridoxine), B12 (cobalamin), and folic acid (B9) are especially known to influence neural functioning. The nine chemical entities that comprise the B complex often are found in the same food sources. Calf's liver and yeast are especially rich in many of the Bs. Asparagus, spinach, bananas, and potatoes all contain B vitamins. But B12 is found only in meats and fish. Although B12 appears to protect the brain against age-related problems, deficiency of the vitamin most often occurs among older adults, as the body's ability to absorb it from food declines with age. There are non-nutritional factors that also reduce levels of B vitamins; at all ages, smoking is chief among them.
Large doses of B6, B12, and folate given for two years slow progression of mild cognitive impairment in the elderly. Normally, brain atrophy accompanies such impairment and progresses to dementia in 50 percent of cases. Brain scans showed that 85 people getting Bs had a 0.76 percent per year rate of atrophy, versus 1.08 percent among 83 people on placebos. "This is a very dramatic and striking result," the researchers say. The vitamins lower levels of homocysteine, a risk factor for stroke.
What role do the low levels of vitamin B12 that are common among the elderly actually play in memory loss? Finnish researchers tracked 271 people ages 65 to 79 for seven years, measuring blood levels of homocysteine and the active form of vitamin B12. None of the 271 had dementia at the start of the study, but 17 developed Alzheimer's over its course. Small increases of homocysteine were linked to large increases in the risk of Alzheimer's, while small increases in B12 levels reduced the risk.
Folic acid supplements may prevent the neurologic deterioration that occurs in the movement disorder Parkinson's disease. Brazilian scientists find that homocysteine levels are 30 percent higher in Parkinson's patients than in controls, and folic acid deficiency is the major determinant of that increase. Both folate deficiency and homocysteine separately exert neurotoxic effects, highlighting the value of keeping up folic acid levels with foods such as liver, lentils, pinto beans, asparagus, and spinach.
Low blood levels of B6, B12, and folate are linked not only to cognitive decline in the elderly but to depression in people of all ages. In a large study in Spain, the prevalence of depression was linked with low folate intake among men who smoke and among men with low anxiety levels. Among women, whose folate levels were generally higher than men's, depression manifested in those with low B12 intake. The vitamins are thought to be involved in production of serotonin and other neurotransmitters.
Even among healthy males in the prime of life, a high-dose B-complex vitamin and mineral supplement has cognitive and mood benefits. In a randomized, double-blind trial, men who got the supplement for 33 days rated themselves less subject to stress and did better on a range of tests assessing mood, mental well-being, and cognitive performance during intense mental processing. The vitamins may protect against mental fatigue in tasks requiring high levels of attention and executive control.