Inclusion of 95 % range in the model to account for inter-individual variability increased the predicted intake of vitamin D needed to maintain serum 25(OH)D ≥ 50 nmol/l to 930 IU/d .
Vitamin D status and sex hormone binding globulin: determinants of bone turnover and bone mineral density in elderly women.
To examine the relation of the vitamin D status and the remaining estrogen activity with bone turnover and bone mineral density ( BMD ) in elderly women , BMD was measured at both hips using dual-energy X-ray absorptiometry and at the distal radius using single photon absorptiometry , in 330 healthy women aged 70 and over .  Vitamin D metabolites , sex hormone binding globulin ( SHBG ) , PTH(1 - 84 ) , osteocalcin , alkaline phosphatase , and hydroxyproline and calcium excretion in 2 h fasting urine were measured . Multiple linear regression was used to adjust for potential confounders . In 65 % of the women , serum 25(OH)D was below 30 nmol/l . Only values below a threshold for 25(OH)D were negatively related to serum PTH(1 - 84 ) ( p = 0.02 , threshold at 25 nmol/l ) and to osteocalcin levels ( p = 0.04 , threshold at 30 nmol/l ) . BMD of the femoral neck and trochanter was positively related to serum 25(OH)D ( left neck p = 0.001 ) with thresholds at 30 nmol/l whereas the distal radius was not ( p = 0.32 ) . Serum PTH was negatively related to BMD at all measurement sites ( all p < 0.001 ) . Serum SHBG , an inverse measure of estrogen activity , was positively related to osteocalcin levels ( p = 0.004 ) and the urinary hydroxyproline/creatinine ratio ( p = 0.002 ) and negatively related to the BMD of the trochanter ( left trochanter p = 0.02 ) and the distal radius ( p = 0.001 ) . We conclude that in elderly women , serum 25(OH)D levels below 30 nmol/l are associated with secondary hyperparathyroidism and increased bone turnover . SHBG is positively related to bone turnover . ( ABSTRACT TRUNCATED AT 250 WORDS
Inclusion of 95 % range in the model to account for inter-individual variability increased the predicted intake of vitamin D needed to maintain serum 25(OH)D ≥ 50 nmol/l to 930 IU/d .