Super-thin women at risk of brittle bone disease

By Anne Harding

NEW YORK (Reuters Health) - Women who are unusually thin but don't have anorexia have poor bone quality that puts them at risk of developing osteoporosis, French researchers report.

The condition, known as constitutional thinness, is so unusual and poorly described that many who have it may be thought, incorrectly, to have anorexia nervosa, Dr. Bruno Estour of CHU Saint Etienne told Reuters Health. "These young thin women are misdiagnosed and stigmatized as anorexic."

"Concerning these young women, it is important to persuade them that no major abnormalities interfere with their health status," he added. Constitutionally thin individuals have a near-normal percentage of fat mass, menstruate normally, and have no abnormalities in hormone secretion or metabolism, Estour and colleagues note in a report.

Researchers have described constitutional thinness among Africans and Australian aborigines, but no efforts have been made to estimate the prevalence of the condition in Western populations, they explain, and there has been no research on bone quality in women with the condition.

To investigate, Estour and colleagues compared 25 women with constitutional thinness to 44 women with anorexia nervosa and 28 normal-weight controls. The anorexic women and those with constitutional thinness all had a body mass index below 16.5.

Bone mineral density in individuals with constitutional thinness was similar to that of women with a long history of anorexia nervosa, and significantly lower than in the controls, the researchers found. Women with constitutional thinness had a higher percentage of body fat than the anorexic women, while their levels of several markers of bone formation and turnover were the same as those of controls.

Overall, 44 percent of the women with constitutional thinness had low bone mass, an "unexpectedly high prevalence," the researchers write.

Females with constitutional thinness have low body weight throughout their growth period and afterwards, while the condition tends to cluster in families, both of which suggest that genes may be a contributing factor, they suggest. Constitutionally thin people might also not have enough weight loading on their bones to build optimum bone mass.

SOURCE: Journal of Clinical Endocrinology and Metabolism, published online Oct. 23, 2007.