Women who are going through the menopause have a higher risk of developing respiratory diseases such as asthma, researchers say.
Researchers looked at women's breathing
In a study of more than 1,200 women, those who had not had a period in the past six months had worse lung function and more respiratory symptoms.
The findings, thought to be due to the effects of falling oestrogen levels, were most pronounced in thin women.
The study is published in the Journal of Allergy and Clinical Immunology.
An international team of researchers measured lung function and asked questions about respiratory health.
They also measured hormone levels in the women who were aged between 45 and 56 years.
The results were similar when the analysis was limited to women who had never smoked.
Women with a body mass index lower than 23 had four times the risk of respiratory symptoms.
Problems were also pronounced in women who were overweight.
Although oestrogen is reduced in all women following menopause, thinner women have the lowest amounts, the researchers said.
At the menopause, the fat cells become the main source of oestrogen, and those who have more fat cells will have higher levels of the hormone, which seems to protect the lungs.
But in very overweight women, it appears that the protective effects of oestrogen are outweighed by other factors.
Dr Francisco Gomez Real, from the University of Bergen, Norway, said: "Clinicians should be aware of increased asthma risk and lower lung function in women reaching menopause.
"These problems appeared to be less pronounced among women with a BMI of 25."
Dr Victoria King, research development manager at Asthma UK, said: "Research is beginning to show a link between menopause and asthma however it is too early to say exactly how menopause affects asthma symptoms and who is likely to be affected.
"What is interesting about this study is that it supports previous findings which show that the effect the menopause may have on lung function is greater in lean women that have a lower body mass index.
"We do know that some women find that their asthma gets worse when they are in a period of hormonal change so it is important to keep an eye on your asthma at these times and discuss any problems you have with your doctor or asthma nurse specialist."