Healthnotes Newswire (December 21 & 28, 2000)—Obesity is associated with an increased risk of cataracts, according to a new analysis of data from the Physicians’ Health Study.

The new research¹ found that men who met the clinical criteria for obesity (as determined by their “body mass index”) were significantly more likely to develop a cataract (lens opacity of the eye, causing progressive vision loss) than were men of normal body weight. The body mass index (BMI) is calculated by dividing the body weight in kilograms by the height in meters squared (kg/m²). A BMI of greater than or equal to 30 is considered obese.

To date, most,^{2 3 4 5} but not all,^{6 7} population studies have found an increased risk of cataracts as BMI increases. The current study, which was published in this month’s edition of the American Journal of Clinical Nutrition, followed over 17,000 apparently healthy male physicians for an average of 14 years. None of the men in the study had a cataract at the beginning of the study. At the end of the follow-up period, approximately 10% of the study participants had developed cataracts. Men with the highest BMI had a 25% greater chance of developing a cataract than did men with the lowest BMI. Another measure of obesity, the waist-to-hip ratio (WHR), also correlated with increased risk; men in the highest WHR category had a 31% higher risk of cataracts than did men in the lowest WHR category.

Cataracts are the leading cause of blindness worldwide, accounting for nearly half of all cases.⁸ The risk of cataracts increases as people age. However, though many people mistakenly assume cataracts are an inevitable consequence of aging, the disease is considered preventable. Delaying the onset of cataracts nationwide would have an enormous impact on healthcare expenditures. It has been estimated that delaying the onset of cataracts by ten years would cut the U.S. cataract surgery rate in half.⁹

How Can Obesity Cause Blindness?

No study, the present one included, has shown that obesity causes cataracts. Studies such as this one, called prospective follow-up studies, cannot prove cause-and-effect; they can only demonstrate risks. Nevertheless, there are several possible explanations of why obesity might contribute to the development of cataracts, and therefore to blindness. Obesity is a risk factor for gout, which has been found to predispose to cataracts.^{6 10 11} Overweight individuals may also have higher amounts of systemic inflammation,¹² which may be a risk factor for cataracts.¹³ Finally, obesity is a strong risk factor for glucose intolerance and insulin resistance, conditions that are involved in the development of type 2 (adult-onset) diabetes.^{14 15} Diabetes is well known to cause or accelerate cataract formation.

The Study’s Limitations

Data on glucose intolerance and insulin resistance were missing from the present study, so the role of these conditions in contributing to the higher incidence of cataracts among obese men could not be evaluated. Also, though researchers were able to control the effects of various confounding variables on their data, they were not able to control for the dietary presence of certain potentially protective nutrients, such as vitamin A, niacin, thiamine, and riboflavin. Moreover, because men with higher BMIs and WHRs tended to consume fewer servings of fruit, vegetables, and whole grains, it is possible that the increased risk of cataracts observed in these men may have been due to diets that were relatively deficient in important vitamins and minerals.

The Perils of Obesity

Obesity is an epidemic in the United States (see Healthnotes Newswire October 5, 2000 edition). Although the results from this study are far from conclusive, they add to the growing list of diseases for which obese people appear to be at greater risk. These include cardiovascular diseases (e.g., coronary heart disease, hypertension),¹⁶ type 2 diabetes,^{17 18} prostate enlargement (called benign prostatic hyperplasia, or BPH),¹⁹ gallstones,²⁰ certain cancers (e.g., breast cancer in postmenopausal women, and cancers of the uterus, colon, and kidney),²¹ female infertility,²² uterine fibroids,²³ work disability,²⁴ and overall mortality.²⁵ The risk of death from cardiovascular disease, cancer, or other diseases increases in overweight men and women in all age groups.²⁶