Vision: The risks of being too fat or too tall

When it comes to cataracts, a major new study finds, body size can make a difference–a potentially blinding one. “This is more bad news for fat people” and especially disheartening at the close of holidays marked by gustatory overindulgence, notes Albert Stunkard of the University of Pennsylvania’s Weight and Eating Disorders Program in Philadelphia.

He’s referring to data from an ongoing study, begun in 1982, of more than 20,000 male physicians. Spurred by inconclusive reports, researchers at Harvard University’s Medical School and School of Public Health, both in Boston, have been investigating whether cataract incidence climbs with increasing weight.

From annual self-reported health questionnaires, the scientists computed each man’s heaviness as gauged by body-mass index (BMI)–weight in kilograms divided by the square of height in meters. Physicians with a BMI over 27.8 faced a 30 percent greater cataract risk than those with a BMI under 22, notes study coauthor Debra A. Schaumberg and her colleagues in the December 2000 American Journal of Clinical Nutrition.

However, BMI does not distinguish between apple-shaped people, who carry most of their excess at the waist, and pear-shaped people, who tend to deposit it at the hips. The former population faces a greater risk of heart and other problems than the latter group does, probably because abdominal fat triggers hormone changes. So, Schaumberg’s team computed waist-to-hip ratios, also.

“We found that among overweight men, apple shapes faced an . . . increased cataract risk that was 30 percent higher than in pear-shaped men,” Schaumberg told Science News. In a related study reported last year, her team showed that men with high concentrations of C-reactive protein, which indicates chronic inflammation, face an elevated risk of cataracts. Work by others has indicated that obese individuals produce excess amounts of C-reactive protein, a risk factor for heart disease (SN: 5/1/99, p. 278).

Obesity may also serve as a marker for other problems that can foster cataracts, such as diabetes or high blood sugar, says Allen Taylor, director of the Nutrition and Vision Research Laboratory at the Agriculture Department’s Human Nutrition Research Center on Aging at Tufts University in Boston.

More perplexing is the cataract link to height. The Harvard scientists found that independent of how fat the men were, those 6 feet and taller proved at least 25 percent more likely to develop cataracts than did men under 5 feet 7 inches. Is this biologically explicable? Perhaps, Schaumberg says, noting that in rodents, calorie restriction stunts stature and cuts cataract risk.

Whatever the mechanism behind these links, both Taylor and Stunkard suspect that the effect of obesity or stature in cataracts is not as large as the effect of age. However, if weight loss could delay cataracts by a decade, the number needing surgical removal would drop by 50 percent, Taylor notes in an accompanying commentary.

Janet Raloff is the Editor, Digital of Science News Explores, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer, specializing in toxicology. To her never-ending surprise, her daughter became a toxicologist.

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