Vitamin D in mild cognitive impairment and Alzheimer's disease. A study in older Greek adults

Background: In recent years, accumulating evidence has linked vitamin D deficiency to cognitive dysfunction and dementia. This study aimed at determining the relevance of serum 25-hydroxyvitamin D concentrations in mild cognitive impairment (MCI) and Alzheimer's disease (AD) in older Greek adults. It also examined whether the vitamin D level could be considered a predisposing factor for conversion from MCI to AD. Methods: The study enrolled 350 subjects aged 65 years and over, allocated into three groups consisting of 103 healthy subjects (HS), 109 individuals with MCI, and 138 patients with AD, respectively. Serum 25-hydroxyvitamin D [25(OH) D] concentrations, measured in ng/ml, were determined by electrochemiluminescence, and we used the Mini-Mental State Examination (MMSE) and the Cambridge Cognition Examination (CAMGOG) to evaluate the subjects' cognitive status. One follow-up examination was performed for the MCI patients 30 months +/- three months after the initial evaluation. Results: Compared to HS, serum 25(OH)D levels were significantly decreased in individuals with MCI (p=0.012) and patients with AD (p <0.001). Moreover, serum 25(OH)D concentrations were significantly decreased in patients with AD compared to individuals with MCI (p=0.003) and also significantly lower in individuals with MCI who progressed to AD compared to those who remained MCI (p=0.028). After adjusting for confounders, multivariate analysis revealed that an increase of vitamin D concentration by one ng/mL reduces the risk of MCI by 4 % (OR=0.96, 95 % CI=0.92-0.99, p=0.006), the risk of AD by 8 % (OR=0.92, 95 % CI=0.89-0.95, p <0.001), and in an individual with MCI reduces the risk of conversion to AD by 10 % (OR=0.90, 95 % CI=0.83-0.96, p=0.003). Conclusions: The present study reveals that serum vitamin D levels are significantly decreased in subjects with MCI and patients with AD compared to HS. Additionally, individuals with MCI who progressed to AD presented significantly lower vitamin D levels than those who remained MCI. These results suggest that preserving adequate vitamin D status in older adults could delay or prevent cognitive decline.