EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
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EW CATARACT 34 Cataract editor's corner of the world by Vanessa Caceres EyeWorld Contributing Writer Does a higher body mass index increase cataract risk? Meta-analysis considers obesity/cataract link H eart disease, diabetes, and metabolic syndrome are just a few of the risks as- sociated with excess body weight and obesity. Could cataract formation be yet another associated risk? A meta-analysis published earlier this year in PLoS One raised this question. 1 The study concluded that an el- evated body mass index (BMI) might increase the risk for age-related cata- ract formation, particularly posterior subcapsular cataracts (PSCs). Study details The study investigators, led by Juan Ye, Department of Ophthalmology, the Second Affiliated Hospital of Zhejiang University, College of Med- icine, Hangzhou, Zhejiang, China, wanted to perform the meta-analysis because the relationship between BMI and the risk of age-related cata- ract has been uncertain in the past. "The relationship between BMI and risk of cataract is controversial across observational studies, with reports of [a] positive linear relation- ship, reduced risk in heavier people, and no significant relationship," the investigators wrote. However, they also noted that prospective data from certain population-based stud- ies, including the Blue Mountains Eye Study, did find that obesity was associated with an increased age-re- lated cataract risk, particularly PSCs. For their meta-analysis, inves- tigators identified related studies via PubMed, Embase, and Cochrane Library searches. They used relative risks and confidence inte vals to determine age-related cataract risk with BMI categories. The studies included had to have a prospective study design and report BMI cate- gories identical to or similar to the World Health Organization's recom- mended body weight classifications. Studies also had to have an outcome measure of incident cataract or cat- aract extraction and follow certain statistical guidelines. Although there were more than 3,900 articles initially identified in their literature search, many were not specific enough for their criteria, and the studies were whittled down to 17. Investigators found a pooled risk ratio for age-related cataract of 1.08 for being overweight and 1.19 for obesity compared with normal weight. "These findings were robust when stratified by sex, sample source, outcome types and confounders, while significantly differed by assessment of BMI and [age-related cataract], and duration of follow-up," investigators wrote. The summary risk ratio suggest- ed that every 1 kg/m 2 BMI increase was associated with a 2% increased age-related cataract risk. "Pooled estimates of risk ratios consistently indicated a trend for subjects with a high BMI to develop PSCs other than nuclear or cortical cataracts," the investigators reported. Although the investigators believe their findings dese ve further study, they noted that the research had some limitations. First, the studies had wide differences in their outcome definitions. Second, the majority of the studies relied on self-reported data from subjects regarding height and weight, which likely led to some inaccurate data. The connection between BMI and cataract formation may have several pathophysiological links, the researchers said. "First, obese individuals have elevated plasma levels of leptin, which might be involved in lens opacity for enhancing accumulation of reactive oxygen species," they wrote. "Sec- ond, individuals with obesity have more intense systematic inflamm - tion with elevated levels of C-reac - tive protein and pro-inflammato y cytokines." A third explanation could be the well-established link between obesity and diabetes, hyperlipidemia, and hypertension, which are all risk factors for cataract. The link between BMI and PSCs could be different patterns of forma- tion and progression of age-related cataract subtypes, the investigators concluded. Endocrinologists weigh in EyeWorld consulted with a few endocrinologists for analysis. "The risk ratios are fairly small overall—1.08 and 1.19—but I still thought it was interesting. It was a meta-analysis so there were no new data, but a meta-analysis can sometimes help illuminate certain associations that might not always be apparent," said W. Timothy Garvey, MD, professor and chair, Department of Nutrition Services, University of Alabama at Birming- ham. Dr. Garvey is also chair of the American Association of Clinical Endocrinologists (AACE) Obesity Scientific Committee. Like the investigators, Dr. Garvey noted that a major limita- tion of the study was that a number T he U.S. expenditure on healthcare rose to more than $3.8 trillion in 2013 and continues to rise. 1 Of that total, it spends nearly $200 billion a year treating obesity and obesity-related diseases, according to a study by the Harvard School of Public Health. 2 While most associate diabetes, heart disease, and hypertension with obesity, this new study examines a new association with cataract formation. If this relationship is in fact true, this brings a new meaning to "eye candy." Bonnie An Henderson, MD, cataract editor References 1. www.forbes.com/sites/danmunro/2014/02/02/ annual-u-s-healthcare-spending-hits-3-8-trillion 2. www.hsph.harvard.edu/obesity-prevention- source/obesity-consequences/economic October 2014