8. No current diagnoses of disorders known to affect bone metabolism including hyperthyroidism, hyperparathyroidism, osteomalacia, or Paget's disease. All participants will be required to have normal serum levels of 25-OH vitamin D (> 20 ng/ml), intact PTH, and thyroid stimulating hormone (TSH). If PTH and/or 25-hydroxy vitamin D (25-OH D) levels are abnormal, subjects may be given calcium and/or multivitamin supplements and be re-tested in 2-12 weeks;