Vitamin D status, parathyroid function and femoral bone density in an elderly Swedish population living at home

Abstract

The aim of this study was to determine vitamin D status and bone mineral density (BMD) in elderly, independent Scandinavians. A cross-sectional examination was conducted in a sample of 104 subjects (mean age 84.5 years), for possible correlations among anthropometric data, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, intact parathyroid hormone (PTH) and femoral neck BMD. Daily dietary calcium and vitamin D intakes were below the recommended levels. Five percent of the subjects were taking calcium, and 30% vitamin D supplements. Previous fragility fracture was reported in 30% of the men, and 55% of the women. Higher mean values of serum 25-hydroxyvitamin D (p = 0.03) and femoral neck BMD (p = 0.03) were recorded in subjects spending > or = 3 hours outdoors weekly. Independently of time spent outdoors, subjects taking daily supplements of vitamin D (on average 5 micrograms) had higher 25-hydroxyvitamin D (p < 0.001) levels, without significant changes in femoral neck BMD values. Serum levels of intact PTH (reference range 8-51 ng/L) were elevated in 41%, of which 5% had mild primary hyperparathyroidism. Serum levels of 25-hydroxyvitamin D (reference range 10-65 ng/mL) and 1,25-dihydroxyvitamin D (reference range 15-55 pg/mL) were below the reference ranges in 4% and 5% of the subjects, respectively. When serum levels of 25-hydroxyvitamin D were lower than approximately 30 ng/mL, the serum intact PTH values began to increase from a level of 43 pg/mL. This threshold most probably reflected a more relevant value of vitamin D insufficiency, indicating that 45% of our subjects rather than 4% actually had hypovitaminosis. Multiple regression analysis demonstrated femoral neck BMD to be significantly and positively associated with higher body mass index, male gender, no history of fragility fracture and 25-hydroxyvitamin D (R2 = 0.39). It is concluded that in this sample of healthy elderly people who regularly spend time outdoors, vitamin D levels leading to secondary hyperparathyroidism seem to be a major cause of osteoporosis. Correcting chronic dietary calcium deficiency is likely to eliminate another factor contributing to poor bone health.