This study is designed to test whether calcium supplementation alone or calcium plus vitamin D reduces the incidence of fractures, reduces high parathyroid secretory activity, and halts bone loss in a population-based sample of women 55+ years of age.

• A calcium supplement of 1400 mg/d will significantly reduce the cumulative incidence of spine and appendicular fractures over four years for independently living, rural women 55 years of age and older compared to similar women on their usual diets.
• A calcium supplement of 1400 mg/d plus 1100 IU vitamin D/d will significantly reduce the cumulative incidence of spine and appendicular fractures compared to a calcium supplement only.

We are conducting a 4-year randomized, double-blind, placebo controlled trial of calcium or calcium with vitamin D supplementation. We randomly sampled the population of healthy, independent living women 55+ years in nine rural counties. We randomly assigned 1180 women to one of three groups: Group 1 receives calcium (1400 mg/d) and vitamin D placebo, Group 2 receives both calcium (1400 mg/d) and vitamin D (1100 IU/d) and Group 3 receives both placebos.

A full-service market research firm randomly selected telephone numbers from all households with listed numbers in the nine-county rural sample area. The firm continued calling until 1180 women were selected who met the inclusion and exclusion criteria and were willing to participate in a four year prospective study of calcium and vitamin D supplementation. The participants were enrolled into study between May 2000 and July 2001.

Participants have study visits every six months. Annually the following are performed: bone density scans, height and weight, brief medical history including medicine changes, fracture surveillance, and compliance with calcium and vitamin D. At baseline and end of study, spine x-rays and dietary recall were obtained.

Inclusion Criteria: healthy women ages 55 and older who were at least four years postmenopausal living independently in a nine-county rural area of Nebraska

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Exclusion Criteria:

1) chronic kidney disease, 2) Paget's metabolic bone disease, and 3) history of cancer except for superficial basal or squamous cell carcinoma of the skin and

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