A red clover preparation of isoflavones has been shown, in a well-controlled study, to significantly reduce the natural loss of bone mineral density in women from 49 to 65.

Introduction

Ever since women became alarmed by the reports of increased health risks associated with hormone replacement therapy (HRT), they've been casting around for a good, safe alternative. The phytoestrogen (plant-derived estrogen) isoflavones are a popular choice. These are compounds in foods derived from plants, especially soy-beans, and are structurally similar to human estrogens.

Estrogens are important for a healthy skeleton, and the lack of them after the menopause is a major risk factor for osteoporosis. HRT was a popular way to retain good bone density, but the risks are now considered too great for this to be a practical solution. Not surprisingly, the question has arisen whether isoflavones could be just as beneficial, without the known risks of HRT. The first part of this question has been addressed in a new study reported in the American Journal of Clinical Nutrition.

What was done

Scientists in Cambridge, UK, recruited women aged 49 to 65 from the local Breast Screening Unit. They had to be free of breast cancer and not currently taking HRT.

The volunteers were asked to provide 24-hour urine samples, which were analyzed for constituents of isoflavones and for various substances indicating the rate of bone turnover. Fasting blood samples were analyzed for estrogen derivatives as well as for markers of bone turnover. Bone density using DXA (dual energy X-ray absorptiometry) was done on the lumbar spine, the neck of the femur, and the bony prominence on the femur, as well as a whole body scan. All these tests were done at baseline and again at 12 months.

After the baseline exam, the participants were allocated randomly to take a red clover isoflavone supplement (Promensil®) daily, which contained 26 mg biochanin A, 16 mg formononetin, 1 mg genistein, and 0.5 mg daidzein, or a dummy placebo that looked identical. The study lasted 12 months.

What was found

A total of 174 women completed the study satisfactorily; their average age was 55, with 17% being premenopausal, 15% perimenopausal, and 68% postmenopausal. Some women in each group failed to complete the study, for a variety of reasons; none of these was serious, except for one woman receiving isoflavones who developed breast cancer 2 months after baseline.

Both groups showed a loss of spinal bone mineral content and bone mineral density. However, the group taking isoflavones had significantly smaller decreases in these two important measures of bone health than those taking the placebo.

There were no significant differences between the two groups with respect to the femur bone mineral content or density; the trend that was observed might have arisen by chance. In the postmenopausal women, however, the tests showed a significant increase in bone formation markers in the isoflavone group, compared with those in the placebo controls.

What it means

These findings were anticipated, based on earlier smaller trials, but this study of isoflavones is one of the longest and largest done to date. Even so, it may only have been long enough to show a beneficial effect in spinal bone, but not in the hip bone. Moreover, it was hardly long enough to reveal the sort of side effects seen with HRT (cancer, stroke, cardiovascular disease). Nevertheless, there seems to be sufficient information from Asia concerning the high consumption of soy to suggest that isoflavones are probably a lot safer than 'classical' estrogens, and they may well offer a reduced fracture risk with long term use.

Source

• The effects of phytoestrogen isoflavones on bone density in women: a double-blind, randomized, placebo-controlled trial. C. Atkinson, JE. Compton, NE. Day,  et al., Am J Clin Nutr, 2004, vol. 79, pp. 326--333

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