Serum 25-hydroxyvitamin D, parathyroid hormone, calcium intake, and bone mineral density in Spanish adults

Vitamin D insufficiency is very common among Spanish community-dwelling adult subjects. A threshold of serum 25(OH)D around 30 ng/ml would be necessary for the prevention of secondary hyperparathyroidism and hip bone loss in our population, regardless of the dairy calcium ingestion.

This study aims to assess 25-hydroxyvitamin D-25(OH)D-status in Spanish adult subjects and to analyze its relationships with serum PTH levels, calcium intake, and bone mineral density (BMD).

A total of 1811 individuals (1154 postmenopausal women and 657 men) aged 44-93 years participated in the study. Serum 25(OH)D, intact parathyroid hormone (PTH), aminoterminal propeptide of type I collagen (P1NP), and C-terminal telopeptide of type I collagen (β-CTX) levels were measured by electrochemiluminescence. BMD was determined by dual x-ray absorptiometry (DXA) at lumbar spine, femoral neck, and total hip.

Serum 25(OH)D levels were below 10, 20, and 30 ng/ml in 5, 40, and 83 % of participants, respectively. There was a significant seasonal difference in mean serum 25(OH)D, with higher levels in summer-autumn. In multivariate analysis, 25(OH)D levels were negatively correlated with age, serum PTH and creatinine, body mass index, smoking, alcohol intake, and a number of chronic diseases, but positively with dairy calcium intake. The magnitude of the difference in serum PTH according to 25(OH)D quartiles was not influenced by calcium intake. A threshold of serum 25(OH)D around 30 ng/ml was observed for serum PTH and hip BMD.

Vitamin D insufficiency is very common among Spanish community-dwelling adult subjects. A threshold of serum 25(OH)D around 30 ng/ml would be necessary for the prevention of secondary hyperparathyroidism and hip bone loss in our population, regardless of the dairy calcium ingestion. Programs to improve vitamin D status may be required in our country.