An adequate calcium intake is important to attain peak bone mass and to oppose that component of age-related bone loss due to insufficient intestinal calcium absorption. Calcium and appropriate vitamin D supplements are particularly important for preventing cortical bone loss and associated hip fractures in the elderly (Type II osteoporosis). Within the initial 5 years following menopause, there is an accelerated loss of trabecular bone from the spine and distal radius (Type I osteoporosis). At that time, estrogen replacement is most effective for preventing the rapid trabecular bone loss that could otherwise result in vertebral or Colles' fractures. During this early period of estrogen deficiency when excessive bone turnover is releasing large amounts of calcium into the circulation, supplemental calcium is ineffective. Progesterone, often given with estrogen to prevent endometrial carcinoma, may itself have a trophic influence on bone.