We undertook this study to determine the prevalence of hypovitaminosis D, its determinants, and its relationships to physical performance, serum parathyroid hormone (PTH) concentration, bone mineral density, and biochemical markers of bone turnover in healthy, ambulatory, pre- and postmenopausal women.
The group studied included 415 women aged 24 to 77 years. Between July and September, we assessed calcium intake and measured serum calcium, phosphorus, albumin, alkaline phosphate, 25-hydroxyvitamin D (25(OH)D), PTH, osteocalcin, and C-terminal cross-linking telopeptide of Type I collagen. We also measured bone mineral density (BMD) by dual-energy radiograph absorptiometry in the spine and total femur. Three tests were used to assess physical performance: timed get-up-and-go test, 5-times-sit-to-stand test, and 2.4 m speed walk.
The prevalence of vitamin D insufficiency (<30 ng/mL) was 91%. In multiple logistic regression, the main determinants of hypovitaminosis D were age >55 years (OR 2.14 [95% IC, 1.1-4.1; P = 0.026)], wearing a veil [OR 2 (95% IC, 1.1-4; P = 0.04)], time spent outdoors less than 30 min/d [OR 2.8 (95% IC: 1.4-5.7; P = 0.003)], and daily calcium intake less than 700 mg [OR 2.39 (95% IC, 1.2-4.7; P < 0.01)]. A significant inverse correlation between 25 OH and osteocalcin (r = -0,18, P < 0001), 25 OH, and Type I collagen (r = -0,15, P = 0003) were observed. By Locally Weighted Regression and Scatterplot Smoothing technique, there was an increase in PTH level when S-25(OH)D was below 30 ng/mL. After adjustment for age, both spine BMD and total femoral BMD failed to show any significant correlation with serum 25(OH)D and PTH. There was no correlation between any physical performance tests and 25(OH)D levels.
Our study showed that during the summer season, vitamin D insufficiency is very common in healthy adult Moroccan women. Lack of sun exposure and veiled clothing style were the most important factors that influenced hypovitaminosis D. Patients with hypovitaminosis D had a high bone turnover, whereas there was no effect on BMD and physical performance. Further research is needed to evaluate the clinical impact of the above findings.