British researchers who discovered the apparent link say cataracts themselves aren't responsible for the increased rate of death. But they may be an indicator that whatever health problem is contributing to the cataracts also may be adversely affecting women's health in other ways.
Cataracts are the leading cause of blindness among American adults; more than half those over the age of 65 have them. A cataract is a clouding of the eye's lens, which results from proteins that clump together and causes a dimmed vision. The cause of cataracts, which can become severe enough to require surgery, is unknown, but smoking, diabetes, sun exposure and other factors are thought to play a role.
Initially, the British team set out to determine what percentage of England's elderly population had cataracts, and what the life expectancies were. The goal was to establish new estimates for the need for cataract surgery. The findings appear in the April issue of the British Journal of Ophthalmology.
The researchers, led by Darwin Minassian of University College London's Institute of Ophthalmology, studied 1,502 men and women 65 and older in north London. Each person was monitored for vision problems and mortality between March 1995 and December 1999.
Among the participants, 184 had diabetes and were studied separately because diabetes is associated with an increased risk of cataracts.
But among the non-diabetic, the researchers found, having cataracts increased the risk of death by 60 percent among women, from 25 per 1,000 to 40 per 1,000. In men, the risk rose from 58 to 63 per 1,000, which was considered not statistically significant.
That was a "striking" difference between men and women, says Minassian. "We expected to find that people with cataracts had higher mortality generally," he says. "We didn't expect to find that this applied to women quite strongly, but not to men at all."
Minassian stresses that the finding does not mean that cataracts are the cause of the higher mortality rates. Instead, he says, it suggests that whatever is causing the cataracts in women in also damaging other body systems, leading to a higher mortality rate.
"Whatever those causes are, they do not appear to be operating in men," says Minassian. He suggests that possible factors might be related to pregnancy, childbearing or hormonal influences.
Dr. William Christen, an epidemiologist at Harvard Medical School in Boston, who has studied mortality associated with cataracts in men, says there are several possible mechanisms that may explain the British researchers' findings.
"It's plausible that the development of cataract could be a marker of underlying disease processes that are related to increased mortality," he says.
"There could be parallel processes," he adds. "Cataract is a chronic disease, it develops over many, many years, so they very easily could share common risk factors.
"Anything that increases the aging process could lead to increased mortality and increased risk of cataract," Christen says. "They're both normal human conditions, and the development of cataract could be a marker of somewhat elevated underlying aging processes," such as atherosclerosis, also known as hardening of the arteries.
"It's an interesting area of investigation," he adds. "If you can identify a subgroup that may be at somewhat higher risk, that's always valuable."