LONDON - Oestrogen-only hormone replacement therapy (HRT) may increase the risk of developing asthma after the menopause, scientists said on Monday.

The findings, from a major study involving almost 58,000 women in France over 12 years, add to a growing body of evidence suggesting a link between some female hormones and asthma.

French and Mexican researchers found that compared with women who had never used any form of HRT, those who did use it were 21 percent more likely to develop asthma, but the risk of asthma was most significant in those using oestrogen alone.

Among these women, the overall risk of asthma was 54 percent higher than for women who had never used any form of HRT, the scientists from the Gustave Roussy Institute in France and the Instituto Nacional de Salud Publica in Mexico wrote in a study in the British Medical Journal?s Thorax publication.

"There is now a large body of evidence suggesting a link between female hormones, including the use of HRT, the development of asthma and its severity," Leanne Metcalf, director of research at the advocacy group Asthma UK, said in a commentary on the study.

"However this is the first large-scale and long-term study to suggest that it is oestrogen-only HRT which significantly increases the risk."

Experts say asthma is more common in young women after they have started having periods, and hospital admissions for asthma are more common among women than men.

The severity of asthma also varies throughout the menstrual cycle and during pregnancy, and the incidence of the disease tends, in general, to fall after the menopause.

HRT can be effective for menopausal symptoms like severe hot flushes and vaginal dryness, but it also carries risks.

Its use has dropped sharply in recent years since a Women?s Health Initiative study in 2002 found an increased risk of ovarian cancer, breast cancer, strokes and other health problems in women on hormone replacement therapy.

However, separate research published last week found that women using HRT were less likely to develop colon cancer. The authors of Monday?s study said that although their findings pointed to an increased risk of asthma, this should be judged "in the light of all the other health effects of HRT use - including its beneficial effect on the quality of life of menopausal women."