Vitamin D and Cognitive Impairment

Background: Vitamin D deficiency is recognized as a significant public health concern, and it has been identified as one of the potentially modifiable risk factors for mild cognitive impairment (MCI). However, evidence regarding the relationship between vitamin D status and cognitive function remains conflicting. Objective: Therefore, this study aimed to examine the prevalence of vitamin D deficiency in the Thai elderly population and an association between vitamin D status and cognitive function, adiposity, and insulin sensitivity. Methods: This study enrolled participants aged 55–80 years with normal cognitive function (normal group) or MCI from the prospective cohort in the “Holistic approach of Alzheimer’s disease in Thai people (HADThai study)”. We used the baseline clinical data to determine the prevalence of vitamin D deficiency and its association between vitamin D status and cognitive function, adiposity, and insulin sensitivity. Results: A total of 718 subjects (71.9% women) with a mean age of 65.7 ± 5.8 years and a mean BMI of 23.9 ± 3.7 kg/m² were enrolled. There were 470 (65.5%) participants with normal cognitive function and 248 (34.5%) with MCI. Vitamin D status did not differ significantly between individuals with normal cognitive function and those with MCI. The prevalence of vitamin D deficiency (<20 ng/mL) and vitamin D inadequacy (<30 ng/mL) in both normal cognitive function and MCI was around 6.5% and 40.0%, respectively. While serum 25(OH)D concentrations were inversely associated with body mass index (BMI), body fat, %body fat, and the homeostasis model assessment of insulin resistance (HOMA-IR), no relationship was found between vitamin D status and cognitive function. Conclusions: Our study emphasized the high prevalence of vitamin D inadequacy among elderly individuals and an inverse association of vitamin D status and adiposity and insulin resistance. These findings emphasize the importance of addressing vitamin D deficiency in the elderly population to improve overall health outcomes. Nevertheless, our results do not support a direct role of vitamin D status in cognitive decline in this population. Further research, particularly studies with longer follow-up periods and the inclusion of patients with dementia with details of vitamin D supplementation, is needed to clarify the potential role of vitamin D in cognitive decline and neurodegenerative diseases.