Exercise
Weight-bearing exercise has also been associated with positive benefits on bone mass or bone density. However, this relationship is not supported by the literature to the extent of dietary calcium and bone mass. Most previous exercise studies are potentially biased because they are nonrandomized, and others have an inadequate sample size to show statistical significance or are compromised by previous physical activity and other confounding factors. One of the few randomized exercise intervention studies was by Snow-Harter in premenopausal women.³ An 8-month weight training or jogging program resulted in a significant increase in lumbar spine bone mineral density. Weight training and jogging resulted in similar increases in bone density (1.2 vs. 1.3 percent, respectively) compared with a slight decrease in the control group.

Calcium and Exercise Interaction
Very few studies have examined the interaction of dietary calcium and exercise. The effects may be independent or additive. Recent studies have evaluated the effect of exercise in addition to calcium supplementation. Lohman et al. reported a positive effect of 18 months of resistance exercise training on femoral trochanter and spine bone mineral density in 56 women ages 28-39 while taking a supplement of 500 mg of calcium in addition to their diet, which averaged 1023 mg/day.⁴ Similarly, in 168 postmenopausal women randomized into one of four groups (placebo, calcium from milk powder, calcium supplements, and supplements plus weight-bearing exercise), exercise in addition to calcium was beneficial for preventing bone loss at the tibia and hip.⁵ Calcium plus exercise was more beneficial at the femoral neck than calcium alone. Thus, in both of these studies, calcium status should have been replete so that a true calcium by exercise effect remains unknown.

Needed Research
Well-designed randomized intervention trials are needed to establish the interactive effects of dietary calcium and exercise on bone health. The effect of type, duration, and intensity of exercise should be evaluated. Although long-term intervention trials through several bone remodeling cycles are of value in evaluating the effect of an intervention, it is also of practical value to determine the effect of cyclic starting and stopping exercise programs. The study of other life style factors that impinge upon both calcium and physical activity requirements for healthy bones is also needed.

1. NIH Consensus Development Panel on Optimal Calcium Intake. Optimal calcium intake. JAMA 1994;26: 1942-8.
2. Teegarden D, Weaver CM. Calcium supplementation increases bone density in adolescent girls. Nutr Res 1994;52:171-4.
3. Snow-Harter C, Bouxsein ML, Lewis BT, Carter DR, Marcus R. Effects of resistance and endurance exercise on bone mineral status of young women: a randomized exercise intervention trial. J Bone Miner Res 1992;7:761-9.
4. Lohman T. Going S. Pamenter R. Hall M, Boyden T. Houtkooper L, Ritenbaugh C, Bare L, Hill A, Aickin M. Effects of resistance training on regional and total bone mineral density in premenopausal women: A randomized prospective study. J Bone Miner Res 1995;10:1015-24.
5. Prince R. Devine A, Dick 1, Criddle A, Kerr D, Kent N. Price R. Randell A. The effects of calcium supplementation (milk powder or tablets) and exercise on bone density in postmenopausal women. J Bone Miner Res 1995;10: 1068-75.