Determinants of vitamin D levels in nursing home residents

Objective: To determine the effect of various doses of vitamin D-2 and D-3, as well as ambulatory status (a surrogate for sun exposure), on 25-OH-D levels. Design: Cross-sectional study with multiple regression analysis. Setting: A state veterans home for veterans and their spouses. Participants: Three hundred two of 609 eligible residents. Measurements: Serum 25-OH-D and parathyroid hormone (PTH) level, supplemental dose of vitamins D-2 and D-3 per kilogram of body weight, and 3 levels of ambulatory status. Results: The mean 25-OH-D level was 28.6 + 9.2 ng/mL; 6.6% of subjects had values of 16 ng/mL or below. Thirty-two percent of participants had 25-OH-D levels below 30 ng/mL and PTH elevation based on stage of kidney disease, evidence that the suboptimal 25-OH-D level had physiologic consequences. Residents unable to transfer independently had 25-OH-D levels 1.6 ng/mL lower than those able to transfer independently. A regression analysis performed in residents unable to transfer independently (less likely to be exposed to the sun) demonstrated that the average increase in 25-OH-D level per 100 IU of D-3 in a 70-kg resident was 2.1 ng/mL versus 1.8 ng/mL for vitamin D-2. Conclusion: Nursing home residents should receive at least 800-1000 IU of D-3 per day in an effort to maintain optimal vitamin D levels.