In a random and prospective study, Alzheimer's disease (AD) patients were assigned to regular sunlight exposure (n = 132) or sunlight deprivation (n = 132) and followed for 1 year. Serum 25-OHD level increased by 2.2-fold in the sunlight-exposed group. Eleven patients sustained fractures in the sunlight-deprived group, and three fractures occurred among the sunlight-exposed group (p = 0.0362; odds ratio = 3.7).

Introduction: A high incidence of fractures, particularly of the hip, represents an important problem in patients with Alzheimer's disease (AD), who are prone to falls and have osteoporosis. We previously showed that 25-hydroxyvitamin D (25-OHD) deficiency caused by sunlight deprivation with compensatory hyperparathyroidism causes reduced BMD in elderly women with AD. This study was undertaken to address the possibility that sunlight exposure with calcium supplementation may maintain BMD and reduce the incidence of nonvertebral fractures in elderly women with AD.

Materials and Methods: In a random and prospective study, AD patients were assigned to regular sunlight exposure (n = 132) or sunlight deprivation (n = 132) and followed for 1 year. BMD of the second metacarpal bone was measured using a computed X-ray densitometer (CXD). The CXD method measures BMD and cortical thickness at the middle of the second metacarpal bone on a radiogram of the hand and an aluminum step wedge as a standard (20 steps; 1 mm/step). Incidence of nonvertebral fractures in the two patient groups during the 1-year follow-up period was assessed.

Results and Conclusion: At baseline, average hospitalization period was 1.7 years in both groups, and activity of daily living (ADL) was decreased. Patients of both groups showed vitamin D deficiency caused by sunlight deprivation and decreased dietary intake of vitamin D with compensatory hyperparathyroidism. The exposed group patients were exposed to sunlight (3615 minutes/year). BMD increased by 2.7% in the sunlight-exposed group and decreased by 5.6% in the sunlight-deprived group (p < 0.0001). Serum 25-OHD level increased from 24.0 to 52.2 nM in the sunlight-exposed group. Eleven patients sustained fractures in the sunlight-deprived group, and three fractures occurred among the sunlight-exposed group (p = 0.0362; odds ratio = 3.7). Sunlight exposure can increase the BMD of vitamin D-deficient bone by increasing 25-OHD concentration and lead to the prevention of nonvertebral fractures.