CHICAGO (AP) - Hormones taken by millions of women at menopause can increase the risk of dry eye syndrome, which in severe cases can affect vision, a study found.

In the study of 25,389 women 49 and older, those taking estrogen alone were about 70 percent more likely to have the syndrome than women not using the supplements. Women taking both estrogen and progesterone faced a 30 percent increased risk.

The findings appear in Wednesday's Journal of the American Medical Association.

It is among the first studies linking hormone supplements to dry eye syndrome, said researcher Debra Schaumberg of Harvard University's Brigham and Women's Hospital.

Hormone supplements relieve symptoms such as hot flashes and night sweats that happen when women's bodies stop making natural estrogen and progesterone. In addition, they can protect against osteoporosis. But they have also been linked to an increased risk of breast cancer.

While the new findings may complicate the already complex decision about whether to take hormones at menopause, Schaumberg said health decisions should not be made "on the basis of a single study."

Dry eye syndrome can be severe and can impair the ability to read, work and drive, but it does not usually cause blindness, she said.

Schaumberg said it is unclear how hormones might cause dry eyes, though she noted that estrogen can inhibit oil-producing glands and might affect a gland in the eyelid that produces an oily substance in tears.

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