COMMENTARY

Healthy Skepticism: Questioning a Study Linking Exercise to Increased Neovascular AMD Risk

Brianne N. Hobbs, OD

Disclosures

January 25, 2018

A Startling Statistic

"Exercising vigorously five or more days a week was associated with a 54% increased risk [for] macular degeneration in men."[1]

This startling statistic from a New York Times article references the results of a large cohort study conducted in South Korea. Certainly the strength of the association is shocking, as is the possibility that exercise, long heralded as a beneficial activity for a myriad of chronic diseases, could actually increase the likelihood of developing a progressive, sight-threatening condition.

Should we all hang up our running shoes, cancel our gym memberships, and start cautioning our patients about the dangers of vigorous exercise? A thorough analysis is needed to understand the results of this study and the potential application in clinical practice.

Study Summary

Rim and colleagues[2] performed a systematic investigation into the potential relationship between neovascular age-related macular degeneration (AMD) and vigorous physical activity. Their cohort study utilized data from 211,960 individuals (mean age, 55.1 years; 43.4% female) included in the South Korean Health Screening Cohort database. The study relied on self-reported frequency of vigorous physical activity, which was defined as "making you sweat." The incidence of neovascular AMD during the study period was the primary endpoint and was determined by diagnosis code and treatment with ranibizumab.

Exactly half of the participants reported engaging in vigorous physical activity, and the other half did not. Researchers controlled for 42 different potential confounders. The incidence of neovascular AMD was higher in the vigorous physical activity group, but only marginally (0.24% vs 0.19%).

Regarding the 54% increased risk cited by the New York Times article, that statistic was generated by a subgroup analysis and was only applicable to a small segment of the study population: East Asian men, aged 45-64 years, exercising vigorously five or more times per week.

Viewpoint

This study falls short of proving a causal relationship between vigorous exercise and neovascular AMD. The strength of the association was relatively weak, and the results are in conflict with previous studies showing a beneficial effect of exercise.

The greatest shortfall of this study, however, was the lack of a biological explanation of how exercise could increase the risk for neovascular AMD. The authors acknowledged this limitation and advised readers that the results should be "interpreted carefully." Despite the limitations of the study, the finding that vigorous exercise might potentially increase the risk for neovascular AMD is important because activity level represents a modifiable risk factor.

The unexpected results of this study illustrate the value of evidence-based medicine in two significant ways. First, hypotheses need to be evaluated using trials because sometimes what we expect to be beneficial actually is not. This study raises important questions about the effects of exercise on AMD. Second, this study highlights the need for duplication of results for validation. This study only included an East Asian population, and its findings may not be broadly applicable to other populations.

The results of this single study are not powerful enough to change how we counsel patients about risk factors for AMD, but hopefully this study will bring more attention to the relationship between exercise and AMD.

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