serum vitamin d status in older adults: a cohort study

Background: vitamin d is best known as a key regulator of bone metabolism and calcium and phosphate homeostasis. this study aimed to assess the effect of different factors on the five-year changes in serum vitamin d concentration among older adults.methods: this cohort study was conducted on adults aged ≥60 years living in amirkola, in the north of iran, from 2012 to 2017. serum 25-hydroxyvitamin d (25-oh vitamin d) concentrations of <20, 20-29.99, and ≥30 ng/ml, respectively, were used to designate vitamin d deficiency, insufficiency, and sufficiency. any variation between the second and baseline values of the 25-oh vitamin d concentration was reported as a five-year difference. data were analyzed using spss version 17.0, and chi square, t test, one-way anova, and tukey hsd post hoc tests were employed. p values less than 0.05 were considered statistically significant.results: the mean serum concentration of 25-oh vitamin d at baseline and follow-up examination in 1011 individuals was 34.68±33.18 and 23.88±14.91, respectively (p<0.001). following a five-year follow-up, vitamin d deficiency, insufficiency, and sufficiency were found in 452 (44.7%), 334 (33.0%), and 225 (22.3%) cases, respectively. the reduction in serum 25-oh vitamin d concentration after five years was significantly influenced by the administration of vitamin d (p=0.013) and calcium (p=0.007) supplements, serum profile of parathyroid hormone (pth) (p=0.010), calcium (p=0.021), and phosphorous (p=0.021). however, age, sex, body mass index, metabolic syndrome, and physical activity had no significant impact (p>0.05). conclusion: regardless of age, sex, body mass index, metabolic syndrome, or physical activity, the mean serum concentration of vitamin d decreased over a five-year follow-up.