Background: Alzheimer's disease (AD) is a chronic neurodegenerative disease characterized by a progressive decline of cognitive performance, which has a harmful impact on social activities. AD is the main cause of dementia and loss of functional independence in the elderly. AD is a worldwide concern because of its adverse consequences and expanding prevalence and incidence. Vitamin D is the most common nutritional deficiency worldwide among children and adults. In addition to its classical function of bone metabolism regulation, vitamin D exhibits multiple biological targets mediated by the vitamin D receptor (VDR). Vitamin D is a risk factor for a wide range of diseases and, as a neurosteroid, has an essential role in nervous system development and protection. Vitamin D regulates mechanisms involved in the pathogenesis of AD, including phagocytosis of amyloid-beta plaques, anti-inflammatory action, antioxidant action, regulation of intraneuronal calcium, ischemic zone size reduction, regulation of choline acetyltransferase enzyme and neurotrophic agents. This study aimed to evaluate the association between AD and vitamin D deficiency.
Methods: In this case-control study, 44 Alzheimer’s disease patients (diagnosed based on DSM-IV-TR criteria) compared with 40 patients that had no disease related to vitamin D. This study was performed in the neurology clinics of Roozbeh and Imam Khomeini Hospitals in Tehran, from April to March 2015. The demographic data were collected. After obtaining informed consent, venous blood was taken by clinical staff to measure the level of 25-hydroxyvitamin D3. Statistical analysis was performed on data.

Results: The Mean age was 71.55 years old (69.88 for females and 73.74 for males) in the case group. Mean vitamin D levels were 26.31 ng/ml and 36.41 ng/ml in case and control groups, respectively. Vitamin D level was deficient (< 30 ng/ml) in 75% of patients, of which 23% were severely deficient (< 10 ng/ml). Statistical analysis showed no significant relationship between Alzheimer's disease and vitamin D levels (P=0.057), but when participants categorized into three groups based on serum vitamin D levels (deficient, insufficient, sufficient), we found a significant relationship between them (P=0.019).
Conclusion: Our results confirm the association between vitamin D deficiency and Alzheimer's disease. Vitamin D supplementation should be considered in individuals at risk of Alzheimer's disease to reach sufficient vitamin D level.