Vitamin D status and secondary hyperparathyroidism: the importance of 25-hydroxyvitamin D cut-off levels

Serum 25-hydroxyvitamin D is the best indicator of vitamin D status. However, some controversy remains regarding "normal" and "abnormal" values. This study's aim was to assess vitamin D status and prevalence of secondary hyperparathyroidism.

A random sample of 326 subjects (164 women and 162 men, aged 68 +/- 9; range, 54 to 89) participating in the European Vertebral Osteoporosis Study (EVOS) was used to assess vitamin D status and secondary hyperparathyroidism. Only those subjects who had never received any kind of treatment for osteoporosis were included in this analysis.

Serum 25-hydroxyvitamin D levels were "deficient" (<10 ng/mL) in 27% of subjects, "borderline" (10-18 ng/mL) in 40% of subjects, and "normal" (>18 ng/mL) in 33% of subjects. The prevalence of secondary hyperparathyroidism (PTH>65 pg/mL) according to 25-hydroxyvitamin D levels was 33% (<10 ng/mL), 16% (10-18 ng/mL), and 12% (>18 ng/mL), respectively. There were no cases of secondary hyperparathyroidism with 25-hydroxyvitamin D levels>40 ng/mL. The independent predictors for PTH were 25-hydroxyvitamin D and serum creatinine in both sexes, but age was a predictor only in men.

These remarkable findings demonstrate the importance of maintaining higher 25-hydroxyvitamin D levels to avoid stimulation of the parathyroid gland.