Association between vitamin D deficiency and cognitive function in the elderly Korean population: A Korean frailty and aging cohort study

It is well known that vitamin D (VitD) plays an important role in bone and calcium metabolism in the human body. VitD has additional roles in the body including modulation of cell growth, neurogenesis, neuroprotection, detoxification, immune function, and reduction of inflammation. Recent studies reveal insufficiency of VitD as a risk factor for cognitive decline or dementia. VitD has a role in normal brain function; insufficiency of VitD may lead to decreased memory and cognitive function. Using 2 years of baseline data from Korean frailty and aging cohort study, 2990 subjects (1415 men and 1575 women) were recruited. A short form of Korean version of the consortium to establish a registry for Alzheimer disease (CERAD-K), an assessment of cognitive status in patients with dementia was used. Among CERAD-K tests, we included word list memory/recall/recognition, digit span (forward, backward), trail making test (TMT) A, and mini-mental state examination in the Korean version of the CERAD assessment packet (MMSE-KC). Serum samples were collected and 25-hydroxyvitamin D (25(OH)D) was measured. Serum 25(OH)D concentrations were classified into clinically relevant categories as: deficient (<10 nmol/L), insufficient (10–30 nmol/L), and sufficient (≥30 nmol/L). The mean age of participants was 76.5 ± 3.9 years, and 52.7% were women. Among 2990 participants, 119 (4.0%) were classified as 25(OH)D deficient and 2253 (75.3%) as insufficient. Only 618 (20.7%) participants were sufficient for 25(OH)D. Among them performance in MMSE-KC, TMT A, and digit span tests was better in sufficient, insufficient, and deficient groups, which was statistically significant (P < .05). However, in multivariable regression analysis after adjusting for age, sex, body mass index, education, center, seasonality, physical activity, and alcohol use, association between 25(OH)D and cognitive function was not statistically significant. Although, when comparing VitD levels, there were differences in cognitive tests among the groups, fully adjusted analysis did not show any association. This result suggests that cognition was not affected by VitD levels alone but also population and sociological variables. In a fully adjusted model, there was no statistically significant association between VitD and cognitive function in the elderly Koreans in logistic regression analysis.