Physical Activity Lowers Odds of Early, Late AMD

Moderate physical activity can potentially reduce the risk of development of early and late age-related macular degeneration (AMD) in white populations between 30-97 years of age, per a meta-analysis of data from 9 studies.

The findings, according to the study's lead author Myra B. McGuinness (pictured), a doctoral student at the Melbourne School of Population and Global Health in Australia, reinforce the "public health message of staying active throughout life."

In order to gain understanding of the connection between AMD and the "positive effects of physical activity on physical aging" and age-related diseases such as AMD, investigators reviewed studies that examined physical activity as a study variable in connection to AMD development or contained data that allowed them to determine an OR [odds ratio] based on exercise as a measure of risk outcome for AMD.

The 9 selected studies, conducted in Europe, Australia, and the United States, were published between 1992 and 2016 and included data from a total of 40870 white participants between the ages of 21 to 97 years of age. McGuinness and colleagues adjusted study data for "age, sex, and smoking to address bias" for other confounding factors contributing to risk.

Pooled data showed that the odds of late AMD were 41% lower among active individuals in comparison to sedentary individuals (n= 28954, OR 0.59, 95% CI), and the odds of early AMD in active versus sedentary individuals showed a small reduction (OR 0.92, 95% CI) in "the odds of early AMD for persons with an active lifestyle."

Each of the studies, according to Guinness, "captured physical activity through self-report using self-administered or interviewer-administered questionnaires" designed to capture data on activity type, intensity, frequency, and context.

The data collected showed that an active lifestyle was "independently associated with lower odds of both early and late AMD, with the effect of being more pronounced for late AMD," supporting the hypothesis that there is a "protective association of physical activity on incident AMD as well as AMD progression."

The study's discussion of data states that there is some caution needed in interpreting the protective effects of exercise alone. McGuiness and colleagues suggest that there is a difficulty in assessing the impact of physical activity alone in relation to increased risk of development or progression of AMD as "persons who exercise tend to eat well, do not smoke, drink in moderation, are more health aware, and use health services for prevention and early detection of disease." The study likewise is limited by the lack of racial diversity in participants, and the lack of "additional confounders in the lifestyle-AMD relationship, such as diet and education."

McGuinness and colleagues hypothesized that even a small to moderate amount of physical activity - as little as 3 hours per week - may be beneficial, but further studies are needed to determine an exact relationship between exercise and its protective benefits on AMD. Further study is also needed to determine the exact cause of the beneficial relationship between physical activity and AMD, which McGuinness suggests may be tied to antioxidant enzyme activity and increased resistance to oxidative stress.

Physical activity has unforeseen protective effects for aging adults in many areas of health, including protections against AMD development and progression. Since moderate physical activity has been repeatedly linked to lower all-cause mortality, the data connecting physical activity and AMD development reinforces the public health emphasis on routine physical activity as a factor in preventing age-related disease.

AMD is the third leading cause of blindness worldwide, and "the primary cause in industrialized countries," according to the World Health Organization. Data shared by McGuinness and colleagues stated that early stages of AMD "affect up to 1 of 3 persons over the age of 70, of whom 10%-20% progress to late-stage disease and are at risk of severe vision loss."

AMD is, per McGuinness is "a complex disease with genetic and environmental risk factors" including many undetermined lifestyle factors which may be modified to reduce the risk for older adults.

The study appears in the May 2017 issue of the American Journal of Ophthalmology.