Bone mineral density of the spine and femur in healthy Saudi females: Relation to vitamin D status, pregnancy, and lactation

Bone mineral density (BMD) measurements of the anterio-posterior lumbar spi ne and the proximal femur using dual-energy x-ray absorptiometry, as well a s relevant clinical and biochemical parameters, were determined in 321 heal thy Saudi females in order to establish reference values and to study the e ffects of physical and lifestyle factors on BMD. Mean +/- SD of age, body m ass index (BMI), number of pregnancies, and total duration of lactation wer e 35.4 +/- 11.3 years, 26.5 +/- 5.2 kg/m(2), 3.1 +/- 3.1, and 23.7 +/- 42.4 months, respectively. Mean +/- SD of serum calcium, 25-hydroxyvitamin D (2 5OHD), and PTH levels were 2.37 +/- 0.09 mmol/liter, 24.5 +/- 17.2 nmol/lit er, and 52.0 +/- 30.8 pg/ml, respectively. Peak BMD values were observed ar ound age 35 years at the spine and earlier at the femur. Compared with USA females, Saudi females had lower weight-matched Z scores at the spine (-0.1 26 +/- 1.078, P = 0.04), femoral neck (-0.234 +/- 0.846, P < 0.0001), and W ard's triangle (-0.269 +/- 1.015, P < 0.0001). Further, the prevalence of o steopenia and osteoporosis in subjects greater than or equal to 31 years ol d were 18-41% and 0-7%, respectively, depending on the site examined. Sever e hypovitaminosis D (25OHD level less than or equal to 20 nmol/liter) was p resent in 52% of the subjects. However, there was no correlation between 25 OHD level and BMD at any site. Parathyroid hormone (PTH) levels correlated significantly with 25OHD levels (r = -0.28, P < 0.0001) and with weight-mat ched BMD Z scores at the spine (r = -0.17, P = 0.005), femoral neck (r = -0 .16, P = 0.007), and Ward's triangle (r = -0.2, P = 0.0008), suggesting tha t the distribution of 25OHD levels in the cohort is below the threshold nee ded for maintaining normal BMD. On the other hand, number of pregnancies an d total duration of lactation correlated with weight-matched BMD Z scores a t the spine (r = -0.17, P = 0.003; r = -0.1, P = 0.08, respectively). We co nclude that BMD in healthy Saudi females is significantly lower than in the ir USA counterparts. This may be due in part to increased number of pregnan cies and longer duration of lactation together with prevalent vitamin D def iciency.