Seasonal prevalence of vitamin D deficiency in institutionalized older adults

OBJECTIVE: To determine the prevalence and seasonal variation of vitamin D deficiency among older residents of longterm care facilities. DESIGN: Cross-sectional survey with 6-month follow-up. SETTING: Three long-term care facilities in Toronto. PATIENTS: Persons more than 65 years old, medically stable, who had resided in the facility for at least 6 months and had no conditions known to interfere with vitamin D metabolism. MEASUREMENTS: Information regarding demographics, past health, and medication use was collected. Mental and functional status were assessed by questionnaire. Venous blood samples were analyzed for alkaline phosphatase, calcium profile, albumin, intact parathyroid hormone, 25 hydroxyvitamin D (250HD), and vitamin D binding protein in September 1994 and March 1995. In a subgroup of patients, bone specific alkaline phosphatase was measured, and dietary intake of vitamin D was assessed. RESULTS: A total of 155 subjects completed the study. The mean age of the subjects was 83.2 years (SD 7.1), and 47% were female. The mean 25OHD level in the March sample (39.9 nmol/L, SD 19.7) was significantly lower than the mean 25OHD level in the September sample (44.9 nmol/L, SD 16.9) (P =.001). The prevalence of vitamin D deficiency in the osteomalacic range (25OHD ( 25 nmol/L) increased from 9% in the fall sample to 18% after the winter (chi(2) = 4.65, P =.03). The prevalence of borderline deficiency or hypovitaminosis D (25OHD <40 nmol/L) increased from 38% in the fall sample to 60% in the spring sample (chi(2) = 14.9, P<.001). Dependence in transfers was associated with an increased risk of hypovitaminosis D, odds ratio 2.08 (95% confidence interval 1.08-4.01), dependence in ambulation 2.57 (1.26-5.23), and regular use of a wheelchair 2.17 (1.09-4.31).When entered into a forward conditional logistic regression model, only dependence in ambulation remained significant, with an adjusted odds ratio of 2.57 (95% CI: 1.26-5.18). CONCLUSIONS: Vitamin D deficiency and borderline vitamin D status are common among older residents of long-term care facilities in Canada. Even though this population has limited outdoor exposure, seasonal variation in the prevalence of deficiency remains significant. Evaluation of interventions to improve the status of vitamin D nutrition in this population is needed.