Calcium Absorption and the Risk for Hip Fracture in Older Women

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The summary below is from the full report titled "Low Fractional Calcium Absorption Increases the Risk for Hip Fracture in Women with Low Calcium Intake.". It is in the 7 March 2000 issue of Annals of Internal Medicine (volume 132, pages 345-353). The authors are K.E. Ensrud, T. Duong, J.A. Cauley, R.P. Heaney, R.L. Wolf, E. Harris, and S.R. Cummings, for the Study of Osteoporotic Fractures Research Group.

What is the problem and what is known about it so far?

As people age, their gut becomes less able to absorb calcium from the food they've eaten. This could be a particular problem for people who already have low calcium intake. Failure to get enough calcium into the body can contribute to the weakening of the bones that happens as people age (osteoporosis), especially older women. The development of osteoporosis is one reason why older people frequently have bone fractures.

Why did the researchers do this particular study?

To find out whether women who had a decreased ability to absorb calcium were actually at greater risk for fractures than women who absorbed calcium normally from the intestine.

Who was studied?

The researchers studied 5452 women 69 years of age or older who were participating in a large study of osteoporosis being conducted in four different areas of the United States. The study did not include black women because osteoporosis is less common among older black women than among white women.

How was the study done?

The researchers measured what fraction of a standardized amount of calcium each woman absorbed into her blood after swallowing a special calcium supplement. They then contacted the women every 4 months to learn whether they had suffered a fracture during that time. The researchers also checked medical records to confirm the occurrence and location of every fracture.

What did the researchers find?

The researchers followed the women for an average of just under 5 years. They found that 729 (13%) of the women suffered a fracture at a location other than the spine; 153 of these were fractures of the hip. After accounting for the effects of age, women who absorbed the smallest amounts of calcium were at increased risk for hip fracture. This association was most striking for women whose intake of calcium was low to begin with. Decreased calcium absorption was not associated with fractures at locations other than the hip.

What were the limitations of the study?

First, it is unclear whether these findings would apply to other population groups. Second, the study was unable to examine spine fractures because the study women did not get regular spine x-rays. Unlike fractures of the hip and other bones, osteoporosis-related spine fractures can occur and be seen on x-ray in women who are unaware that they have had a fracture.

What are the implications of the study?

Decreased calcium absorption can increase the chance of osteoporosis-related hip fractures in older women, especially when it occurs in women with low dietary calcium intake. This study suggests that it may be useful to find ways to improve calcium absorption and emphasizes the importance of getting enough calcium in the diet.