Background: Plasma folate and vitamin B12 are involved in homocysteine metabolism, and both are commonly deficient in older populations. In previous studies, homocysteine has been implicated Alzheimer disease, yet population based studies on these B vitamins and cognitive function in non-demented subjects have been limited and inconsistent. Objective(s):We examined the relationship between plasma folate and B12 levels and cognitive function among 619 older participants of the Nurses Health Study (NHS). Methods: The NHS is an ongoing, prospective cohort of female nurses; in 1989–1990, blood samples were collected from one-third of participants. From 1995–2001, subjects aged 70 years or above, and free of stroke completed a telephone cognitive interview consisting of tests measuring general cognitive ability, episodic memory, category fluency and attention. Participation was high, at 93%. In total, 619 women also had plasma folate and b12 levels measured, as controls in other cohort research projects. We performed multivariable analyses of plasma levels of these B vitamins in relation to cognitive performance, adjusting for numerous potential confounders. Results: We found little relation between plasma folate and cognitive function; for example, after adjustment, women in the highest quartile of plasma folate (>=13 ng/mL) scored 0.09 units higher (95% CI=-0.08, 0.25; p-linear trend=0.40) on a global composite score combining all cognitive tests, compared to the women in the lowest quartile. On the other hand, women in the highest quartile of plasma vitamin B12 levels (>=541 pg/mL) scored significantly higher by 0.18 units (95% CI=0.02,0.34; p linear trend=0.05). In our cohort, each year of age was associated with a deficit of 0.05 units, thus having highest B12 levels was cognitively equivalent to being about 4 years younger in age. Women who were in the highest quartile for both plasma folate and vitamin B12 performed significantly higher by 0.22 units (95% CI=0.01, 0.42) compared to women in the lowest quartiles for both nutrients. Conclusions: Higher levels of vitamin B12, especially in combination with high folate levels, may be associated with better cognitive performance many years later among older women.
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