Two new studies suggest that adequate intakes and blood concentrations of vitamin D may be preventive in cognitive decline and Alzheimer’s disease in older women.
In a French study, 498 women aged 75 years and older and free of vitamin D supplements were divided into three groups according to the onset of dementia within seven years: participants who developed Alzheimer’s disease (AD), other dementias or no dementia (1). The women’s vitamin D dietary intakes were estimated at the beginning of the study from a self-administered food frequency questionnaire. The study results showed that after considering potential confounders (e.g., initial cognitive performance, education level, physical activity, sun exposure, disability, number of chronic diseases, depression, use of psychoactive drugs, and season) higher vitamin D dietary intake was associated with a lower risk of developing AD. Women who developed Alzheimer’s disease had lower vitamin D intakes (an average of 50.3 µg per week) than those who developed other dementias (an average of 63.6 µg per week) or no dementia at all (an average of
59.0 µg per week).
In a US cohort study, blood vitamin D concentrations and the degree of cognitive decline was measured in 6,257 elderly women for four years (2). The study results showed that women with very low vitamin D levels (below 10 ng/mL resp. 25 nmol/L) had a significantly higher risk of developing cognitive impairment than participants with higher blood vitamin D concentrations (above 30 ng/mL resp. 75 nmol/L). Among cognitive-ly-impaired women, low vitamin D levels (less than 20 ng/mL) were associated with a higher risk of cognitive decline.
Earlier studies had already associated insufficient vitamin D intakes and blood concentrations with cognitive decline among older adults (3). The relationship between vitamin D and cognitive decline is not well under-stood.