Exercise at Menopause: A Critical Difference

Margaret Burghardt, MD

Disclosures

Medscape General Medicine. 1999;1(3) 

In This Article

Osteoporosis: Exercise vs Calcium Supplementation

The skeleton contains 99.5% of total body calcium. Sufficient calcium is vital to the formation of healthy bone. Rapid bone loss in the early menopausal years is mainly due to lack of endogenous estrogen, and it is not clear whether this loss can be prevented by calcium supplementation alone. The current recommended dietary intake of calcium for postmenopausal women is 1500mg/day. A high dietary balance of calcium does seem to be protective against the risk of future fractures.

For example, a study of women from 2 towns in Yugoslavia found that the premenopausal and postmenopausal inhabitants of a town with a higher individual daily calcium intake had greater metacarpal cortical area than residents of another town with lower calcium intake.[27] Among postmenopausal women in the study, the fracture rate was also significantly higher in the town with lower calcium intake. Calcium supplements given to premenopausal women do increase bone density.[2]

Dietary calcium supplementation seems to exert its greatest effect in the early years of peak bone formation (ie, before age 25) and much later, 5 or more years after the onset of menopause. The role of calcium alone in maintaining bone mass in early postmenopausal women is less well supported.

In one study for example, Riggs and colleagues[28] observed no difference in rates of spinal bone density loss in 2 groups of 106 women (aged 23-84 years) with significantly different mean calcium intake (range, 260-2035mg/d), 61 of whom were postmenopausal. Similarly, Dawson-Hughes and associates[29] found that early (<6 years) postmenopausal bone loss from the spine was accelerated regardless of calcium supplementation. Calcium seems to positively affect bone density at the spinal radius, but its role at the spine itself is less clear.[12,29]

Those most likely to benefit from calcium supplementation are women with low dietary calcium intake (<600mg/day). In one study, calcium citrate malate (500mg dose) was found to be more effective than calcium carbonate (500mg dose) in preventing bone loss from sites at the spine, femoral neck, and radius.[29] Calcium citrate malate is better absorbed but is more expensive than calcium carbonate.

There appears to be a synergistic effect of exercise and calcium on trabecular bone in postmenopausal women.[5] This combination of exercise and calcium supplementation (1g of elemental calcium per day in the form of calcium lactate-gluconate) slowed bone loss when compared with exercise alone. Figure 4 shows increased exercise and increased distal-forearm bone density, with bone-density improvements slightly greater in the exercise group that also received calcium.

Short-dashed line shows positive correlation between baseline level of physical activity and mean change in distal-forearm density in an exercise-only group during a 2-year study period. Physical activity was measured in metabolic equivalents (METs) (y=0.07x-32; r=0.37; P=0.02). One MET is defined as energy consumed per minute of sitting at rest. Long solid line shows positive correlation between baseline serum calcitriol concentration and mean change in distal-forearm bone density in an exercise-calcium group over same study period (y=0.11x-12.19; r=0.54; P=0.001). Data from Prince et al. [45]

Exercise and ERT are also believed to act synergistically to prevent bone loss[5,30] (Fig. 5). In a study by Notelovitz and associates,[31] surgically menopausal women (eg, due to hysterectomy, ovariectomy, etc.) (n=20) increased spinal (P=0.004) and radial (P=0.01) bone density with exercise and ERT (0.625mg conjugated estrogen) compared with matched women using exercise alone.

Comparison of bone-density effects of exercise alone (dotted line), exercise along with supplemental calcium (dashed line), or exercise with estrogen therapy (solid line). Measurements are means ± SE of bone density of distal-, median-, and proximal-forearm sites during a 2-year study period. Data from Prince et al. [45]

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