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MADISON, Wis. -- Regular exercise three or more times a week reduced the risk of developing age-related macular degeneration by as much as 70%, researchers here reported.
MADISON, Wis., Oct. 31 -- Regular exercise reduced the risk of developing age-related macular degeneration by as much as 70%, researchers here reported.
Even walking more than 12 blocks a day was beneficial, reducing the risk by 30% compared with a sedentary lifestyle, Michael Knudtson, M.S., of the University of Wisconsin, and co-authors, reported online in the British Journal of Ophthalmology.
Cardiovascular disease and age-related macular degeneration may share common risk factors, such as weight, blood pressure, systemic inflammation, and endothelial dysfunction, they noted, and physical activity is known to improve the heart-risk profile. The Wisconsin team investigated a relationship between physical activity and the long-term rate of degenerative eye disease.
The population-based findings came from an analysis of the 15-year cumulative incidence of the degenerative eye disease among 3,874 men and women in Beaver Dam, Wisconsin.
Participants in the Beaver Dam Eye Study were ages 43 to 86 at the start of the 15-year study in 1988-1990. After that, they were assessed at five-year intervals with grading stereoscopic color fundus photographs. Measures of physical activity-blocks walked each day, stair climbing, and sessions of formal exercise--were obtained through a questionnaire at the baseline examination.
In all, 25% of the population reported an active lifestyle (regular walking three or more times a week), 21% climbed more than six flights of stairs a day, while 13% walked more than 12 blocks a day.
After controlling for age, sex, history of arthritis, systolic blood pressure, body mass index, smoking, and education, those with a baseline active lifestyle (walking three times or more a week) were 70% less likely to develop exudative age-related macular degeneration over 15 years (odds ratio 0.3, 95% confidence interval 0.1 to 0.7), compared with sedentary people.
After multivariate adjustment for other risk factors, such as age, serum lipid levels, and weight, increased categories of number of blocks walked per day decreased the risk of developing the eye disorder over 15 years by 30% (OR 0.7, CI 0.6 to 0.97).
However, physical activity was not related to the incidence of early age-related macular degeneration or pure geographic atrophy, the researchers reported.
After stratifying by age, sex and BMI, the only significant interaction was between age and walking. People younger than 65 at baseline who walked did not reduce their risk; those older than 65 had a 50% decreased risk (OR 0.54, CI 0.37 to 0.80; P value for interaction =0.04).
Those with an active lifestyle were more likely to be younger and after controlling for age were less likely to be current smokers, have a history of heavy drinking, have less education, or a larger body mass index. However, they were more likely to have a history of cardiovascular disease than those with a sedentary lifestyle, the researchers reported.
Physical activity in the Beaver Dam population was associated with lower systolic blood pressure, lower white blood counts, and less obesity, factors previously found to be linked to macular degeneration, the researchers said. However, they added that the relationship of walking and an active lifestyle with a lower rate of the eye disorder remained even after controlling for these factors.
Although other factors, such as diet may contribute to these findings, physical activity is known to reduce systemic inflammation and endothelial dysfunction, both hypothesized to have a role in the pathogenesis of age-related macular degeneration. It is not clear, the researchers said, whether specific inflammatory markers, such as C-reactive protein, or other unmeasured confounders are the explanation for the association.
The age association in this form of macular degeneration is more relevant biologically than chronologically, the investigators noted, adding that physically active people are likely to be biologically younger than sedentary individuals.
The study's limitations included the measurement of physical activity by a questionnaire and the fact that sedentary individuals were less likely to return for follow-up exams. Still, the researchers said, they believe that these limitations would bias the findings toward the null. Finally, they noted that they could not rule out the possibility of residual confounding.
Summing up, the Wisconsin team said that independent of body mass index and other confounders, this study provides evidence that a modifiable behavior, regular physical activity such as walking, might protect against the age-related eye disorder.