Gain in bone mass occurs in healthy young women during the third decade of life. Physical activity and dietary calcium intake both exert a positive effect on this bone gain. Use of oral contraceptives exerts a further independent positive effect. Changes in life-style among college-aged women, involving relatively modest increases in physical activity and calcium intake, may significantly reduce the risk of osteoporosis late in life.

Transilial bone biopsies were obtained from 34 healthy postmenopausal women following in vivo fluorochrome labeling. Stained and unstained undecalcified sections were evaluated using a Merz grid. Standard histomorphometric data from cancellous bone tissue were collected and the results were evaluated and presented as variables commonly used in bone histomorphometry. The normal ranges, medians, means, and standard deviations for the group of 34 are presented in tabular form for structural, surface, basic dynamic, and derived dynamic data. Similar data for individuals grouped by ages 45-54, 55-64, and 65-74 are also presented. Secular trends for the whole group are evaluated. The structural and surface data are not much different from previous reports of sudden-death accident victims, when methodologic differences are considered. The mineral apposition rate (MAR) was 0.53 +/- 0.08 micron/day, similar to previous reports in cancellous bone, but one-third less than in cortical bone. MAR showed a marked decline with age. In contrast, the extent of tetracycline-labeled surfaces varied widely without a secular trend. Double-label surface (dLS/BS) ranged from 0.5 to 8.0% and single-label surface (sLS/BS), from 0.5 to 10.5%. Mineralizing osteoid surface (MS/OS) varied from 2 to 64%. Using only double-label surface to represent mineralizing surface, volume-based bone formation rate (BFR/BV) ranged from 0.7 to 28%/yr, and the remodeling period (Rm.P) varied from 0.28 to 4.5 years. Calculations using other representations of mineralizing surface [double plus one-half single label (MS/BS"); all label (MS/BS')] are also presented. These bone histomorphometric data are important because: (1) they come from a cohort of living subjects that was recruited solely for the purpose of establishing normal bone histomorphometry; (2) they represent the age range of patients with postmenopausal osteoporosis; and (3) they markedly expand the bone histomorphometric database of healthy persons given in vivo fluorochrome labeling prior to transilial biopsy.

We tested the spine antifracture and bone sparing efficacy of 1.2 g/day of oral calcium as carbonate in two groups of elderly women, one with prevalent fractures (PF, n = 94) on entry and the other without (NPF, n = 103). It was a prospective randomized, double-blind, placebo-controlled trial in mostly rural communities in women over age 60 who were living independently and were consuming < 1 g/day of calcium. We obtained annual lateral spine radiographs and semiannual forearm bone density over 4.3 +/- 1.1 years and determined vertebral fractures by radiographic morphometry augmented by physician assessment. In the PF group, 15 of 53 subjects on calcium had incident fractures, compared with 21 of 41 on placebo (p = 0.023, chi2). Calcium did not reduce the rate of incident fractures in the NPF group. Those with a prevalent fracture on entry and not treated with calcium were 2.8 times more likely to experience an incident fracture than all others. Change in the forearm bone mass on placebo in the PF group was -1.24 +/- 2.41%/year compared with +0.31 +/- 1.80%/year on calcium (p < 0.001). In the NPF group, the difference was less: -0.39 +/- 2.08%/year versus 0.00 +/- 1.64%/year (p = 0.2). We conclude that in elderly postmenopausal women with spine fractures and selfselected calcium intakes of < 1 g/day, a calcium supplement of 1.2 g/day reduces the incidence of spine fractures and halts measurable bone loss.

The effect of coingestion of a meal on calcium absorption efficiency was investigated using Ca carbonate, milk, and a new Ca delivery system, CCM. Six experiments with 168 rats and two experiments with 46 normal young women showed that coingestion of a light meal of varied composition enhanced absorption efficiency from all three sources by 10-30% above levels achieved when the test load was ingested without other foods. The differences taken as a whole were highly statistically significant.

Absorption of calcium from white, red, and pinto beans, labeled with 45Ca, was measured in 24 women in a three-way randomized design using a calcium load of 72 mg and milk as the referent. Fractional absorption for the three beans averaged 0.219 + 0.047 and did not differ by type. Milk calcium absorption at the same load was more than two times higher, 0.451 r 0.088 (P