Calcium Supplementation in Postmenopausal Women

Susan A. New, BA, MSc, PhD

Disclosures

September 04, 2003

Question

How important is calcium intake to bone health for postmenopausal women?

Response from Susan A. New, BA, MSc, PhD

Predisposition to poor skeletal health resulting in osteoporotic fracture is a major public health problem. There can be no doubt that the future economic impact of osteoporosis is going to be phenomenal. It is important to think clearly about the 2 principal determinants in adult bone health: (1) maximum attainment of peak bone mass (PBM) in young adulthood and (2) the rate of bone loss with advancing age. With the onset of the menopause, rapid bone loss occurs, which is believed to average approximately 2% to 3% over the following 5-10 years, being greatest in the early postmenopausal years. It is important to note that bone mass continues to decline with age but at a slower rate than during the early menopausal time. However, there is some evidence that in those elderly individuals most at risk of "undernutrition" in the later years, the menopausal period is a crucial time with respect to their increasing risk of fracture.

Both PBM attainment and rate of postmenopausal bone loss are regulated by a combination of endogenous factors (nonmodifiable factors such as genetics and race) and exogenous factors (modifiable factors such as nutrition and physical activity). Genetic influences are believed to account for up to 75% of the variation in bone mass, but there is still plenty of room for modifiable factors to play a vital role. Certainly we know that weight-bearing physical activity is beneficial to the skeleton, but clarification of the exact type, intensity, and duration required for optimum bone mass is still urgently needed.

The importance of calcium to bone remains controversial. The past 2 decades have been a time of marked controversy as to the effectiveness of calcium supplements in reducing peri/postmenopausal bone loss.[1,2] The failure of many studies of women at the postmenopausal stage to identify the special circumstances created by estrogen deficiency in the years following hormonal decline may help to explain the disagreement among studies as to whether calcium is effective in reducing bone loss. In 1990, Dawson-Hughes's study[3] was the first to divide women into years past the menopause. Calcium supplementation (500 mg/d) failed to reduce bone loss in women who were less than 5 years postmenopause, but in women who had been postmenopausal for 6 years or more, bone loss was significantly reduced with a daily intake of < 400 mg/d.

This finding has received further support from other supplementation studies that have divided women according to their time since menopause. All of these show a positive effect of calcium supplementation in reducing late postmenopausal bone loss.[4] The studies by Reid and colleagues[5,6] provide evidence that calcium is still effective in reducing bone loss after 4 years of supplementation.

Thus, there is now a general consensus of agreement that calcium is effective in reducing bone loss in late postmenopausal women,[7] particularly in those women with low habitual calcium intake (< 400 mg/d). Results of trials in the early postmenopausal stage remain inconclusive, and this is an area that still requires considerable attention.

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