NEW YORK (Reuters Health) - On top of all the other problems related to being very overweight, researchers now report that obesity can increase the risk of developing cataracts, the world's leading cause of blindness.

Cataracts occur when proteins in the eye's lens begin to clump together, forming a milky cloud that obscures vision. Everyone will experience some clouding in the eye lens if they live long enough.

But according to new findings, the risk rises in tandem with body mass index (BMI), a measure of weight in relation to height. A BMI below 25 is considered healthy while obesity is marked by a BMI of at least 30. Those who fall in the middle are considered to be overweight or at risk for a host of chronic disorders.

In the study, middle-aged men and women with a BMI of at least 30 were 36% more likely than their leaner peers to develop cataracts. There was no relationship between obesity and nuclear cataracts, the most common type of cataract that strikes the center of the eye. The risk of developing a posterior subcapsular cataract, the most visually disabling type that forms in the back of the lens, rose by 68% among obese adults, the investigators found.

It is not clear from the current report how obesity may contribute to cataracts, but the researchers suggest that poor blood sugar control or elevated levels of inflammatory compounds in the body, both of which can occur in obese individuals, may play a role.

While more research is needed, the report published in the International Journal of Obesity indicates that maintaining a healthy body weight may prevent or delay the onset of cataracts and reduce the need for cataract surgery, which involves removing the cloudy lens and replacing it with an implant.

Although cataract surgery can restore vision, it is costly and not available in less developed countries, according to Dr. June M. Weintraub, currently with the San Francisco Department of Public Health in California, and her colleagues from the Harvard School of Public Health in Boston, Massachusetts.

"Obesity is related to numerous chronic diseases, and the causal relationship between obesity and cataract extraction...adds further indication of the burden of obesity on our society," Weintraub explained in an interview with Reuters Health.

She suggested that understanding that obesity can increase the risk of developing cataracts might motivate some individuals to control their weight.

The study involved more than 130,000 US adults aged 45 years and older who did not have a cataract when the study began. Over the next 10 to 16 years, researchers tracked the development of cataracts and their relationship to BMI.

SOURCE: International Journal of Obesity 2002;10.1038/sj.ijo.802158.

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