Two studies in the May 2004 issue of the New England Journal of Medicine present evidence that a high level of the amino acid homocysteine is associated with increased risk of osteoporotic (fragile bone) fractures. Elevated homocysteine already is known to be a risk factor for heart attack and stroke and homocysteine testing is often included in cardiac risk assessment. It also is used to determine if a person is folate- or B12-deficient since homocysteine has been found to be increased in both of these conditions.

In one study, the risk of fracture was analyzed based on data from over 2000 patients over the age of 55. Researchers found that those in the quarter with the highest levels of plasma homocysteine had almost 2 times the risk of fracture than those in the other quarters. The risk seemed to be independent of other factors, such as bone mineral density.

In the other study, data from nearly 2000 patients ages 59 to 91 were examined. These researchers found that men and women in the highest quarter for plasma homocysteine had almost 4 and 2 times, respectively, the risk of hip fracture than those in the lowest quarter. Scientists involved in these studies concluded that elevated homocysteine is an important indicator of high risk for fractures among older people.

The question remains whether the high levels of homocysteine are causative – affecting bone fragility – or merely associated somehow with bone fractures. For example, homocysteine is elevated in individuals who suffer from poor nutrition, such as those who are folate-deficient, and there have been some studies linking folate deficiency with low bone mineral density. It, therefore, could be the nutritional deficit causing the fractures, not the elevated homocysteine. Researchers currently are trying to better understand the factors involved in bone loss and the connection with homocysteine so it can be determined how to make the best use of this new information.

For now, it appears that measuring homocysteine may be useful in assessing the potential risk of fractures. However, whether a reduction in homocysteine levels, such as through changes in diet, can reduce the incidence of fractures has yet to be proven. Those at high risk would need to take other preventive measures to avoid fractures.

Sources:
Raisz, L. Homocysteine and Osteoporotic Fractures – Culprit or Bystander? (Editorial) New England Journal of Medicine. 350; 20 (pages 2089-2090). (www.nejm.org)

van Meurs, J, et al. Homocysteine Levels and the Risk of Osteoporotic Fracture. New England Journal of Medicine. 350; 20 (pages 2033-2041).

McLean, R. et al. Homocysteine as a Predictive Factor for Hip Fracture in Older Persons. New England Journal of Medicine. 350; 20 (pages 2042-2049).