October 2014

 

CATARACT

 

Cataract editors corner of the world

Does a higher body mass index increase cataract risk?


by Vanessa Caceres EyeWorld Contributing Writer

 
 

The 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

Were in a changing time of recognizing obesity as a disease. This could be yet another reason to prevent obesity. That may be jumping ahead, but that would be the implication.

W. Timothy Garvey, MD

 

Meta-analysis considers obesity/cataract link

Heart disease, diabetes, and metabolic syndrome are just a few of the risks associated 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 elevated body mass index (BMI) might increase the risk for age-related cataract 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 Medicine, Hangzhou, Zhejiang, China, wanted to perform the meta-analysis because the relationship between BMI and the risk of age-related cataract 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 relationship, reduced risk in heavier people, and no significant relationship, the investigators wrote. However, they also noted that prospective data from certain population-based studies, including the Blue Mountains Eye Study, did find that obesity was associated with an increased age-related cataract risk, particularly PSCs. For their meta-analysis, investigators identified related studies via PubMed, Embase, and Cochrane Library searches. They used relative risks and confidence intervals to determine age-related cataract risk with BMI categories. The studies included had to have a prospective study design and report BMI categories identical to or similar to the World Health Organizations recommended body weight classifications. Studies also had to have an outcome measure of incident cataract or cataract 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 suggested that every 1 kg/m2 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 deserve 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. Second, individuals with obesity have more intense systematic inflammation with elevated levels of C-reactive protein and pro-inflammatory 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 formation 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 overall1.08 and 1.19but 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 Birmingham. 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 limitation of the study was that a number of studies relied on subjects self- reporting their health information. Its well-known that people over represent their height and under represent their weight, he said. The self-reported aspect is a severe limitation, said endocrinologist Sarfraz Zaidi, MD, Los Robles Hospital, Thousand Oaks, Calif. However, even in the studies where researchers measured height and weight, there was a correlation between obesity and cataract formation. Endocrinologist Gregory B. Dodell, MD, in private practice, and attending physician at Mount Sinai Roosevelt, New York, addressed the investigators theories on the connection between obesity and cataract formation. They hypothesize that as BMI increases, there tends to be an increase in systemic inflammation via cytokines and C-reactive protein, which may predispose to cataract formation. Widespread inflammation is detrimental to organ systems as a whole and may be the likely culprit for cardiovascular disease, renal disease, and cancer. The mention of leptin, which is a satiety hormone, and the accumulation of free radicals is an intriguing thought. Dr. Dodell would have liked the researchers to comment on subjects physical fitness and nutrition. He also noted that BMI can be a deceiving marker for obesity, as sometimes physically fit, healthy people could still have a higher BMI.

Dr. Garvey said this study is part of the accumulating body of research into obesity. Were in a changing time of recognizing obesity as a disease. This is a position that the AACE is taking, rather than saying obesity is a lifestyle choice, he said. This could be yet another reason to prevent obesity. That may be jumping ahead, but that would be the implication. If further research finds a stronger link between obesity and cataract, practitioners would want to emphasize prevention, since weight loss would likely not help once cataracts form, Dr. Garvey said. It remains to be seen to what degree cataract risk is related to insulin resistance and not to the obesity per se,Dr. Garvey added.

Cataract formation could turn out to be a lesser-known risk factor associated with obesity, Dr. Zaidi said. Other lesser-known risk factors include fatty liver, sleep apnea, polycystic ovary syndrome, and even vitamin D deficiency.

Reference

1. Ye J, Lou C-X, He J-J, Xu Y-F. Body mass index and risk of age-related cataract: A meta-analysis of prospective cohort studies. PLoS One. 2014;9:e89923.

Editors note: The physicians interviewed have no financial interests related to their comments.

Contact information

Dodell
: dodellmd@gmail.com
Garvey: garveyt@uab.edu
Zaidi: contact@doctorzaidi.com

Does a higher body mass index increase cataract risk? Does a higher body mass index increase cataract risk?
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