Women who have an overall healthy lifestyle — who eat lots of fruits and vegetables (and other healthful foods), exercise regularly and don’t smoke — may be at significantly reduced risk of developing age-related macular degeneration (AMD), a study published Monday in the Archives of Ophthalmology has found.
In fact, the combination of those healthy lifestyle behaviors lowered the relative risk of AMD among the women studied by 71 percent — much more than did any one of those behaviors by itself.
That’s a key take-home message of this study. “People want to isolate and find the magic bullet, the one thing that we should change,” said Julie Mares, the study’s lead author and a nutrition professor in the department of ophthalmology and visual sciences in the University of Wisconsin-Madison’s School of Medicine and Public Health, in a phone interview last week. “But I think we could be misunderstanding the importance of overall healthy lifestyles if we only look at each factor alone.”
A high personal and societal toll
AMD is an eye disorder characterized by the blurring or loss of central vision. It affects an estimated 1.8 million Americans over the age of 40, according to the Centers for Disease Control and Prevention. Another 7.3 million people in the U.S. have detectable eye changes (early AMD) that put them at risk of developing the disorder.
In addition to the devastating personal burden it imposes on individuals, AMD takes a significant financial toll on our health-care system. The direct medical costs of treating AMD are estimated at $575 million annually, according to a 2006 analysis. Those costs will only rise as the American population ages.
Some of the more consistent individual risk factors linked to AMD in past research have been diets high in fat or low in the plant pigment lutein. (Lutein is found primarily in green leafy vegetables.) Smoking, too, has been associated with an increased risk. The role of obesity in raising the risk of AMD is less clear, and physical activity’s impact on the disorder hasn’t been studied much at all.
The current study is the first one to estimate the combination effect of all these lifestyles together on AMD risk, said Mares.
Crunching the data
Mares and her colleagues analyzed data from detailed questionnaires completed by 1,313 women (aged 50 to 68 at enrollment) who were part of the Carotenoids in Age-Related Eye Disease Study, an offshoot of the Women’s Health Initiative study. Six years (on average) after the questionnaires were filled out, special photographs were taken of the backs of the women’s eyes to look for the telltale signs of either early or advanced AMD.
Some 202 women in the study were found to have those signs. Most of those women (94 percent) were in the early stages of the disorder and weren’t even aware of its presence.
A detailed analysis showed that the women with the highest healthy-diet scores (in the top 20 percent, or quintile) were 50 percent less likely to develop early AMD than those with the lowest scores (the bottom 20 percent). This association was stronger than any observed for a single nutrient. (A healthy diet was one that contained a high intake of fruits, vegetables and whole grains and a low intake of refined sugar and fat.)
In addition, women in the highest quintile for physical activity (8 to 10 hours of light to moderate activity per week) were 54 percent less likely to develop AMD than those in the lowest quintile.
In this study, smoking was not found to be independently associated with AMD risk, perhaps, said Mares, because so few women in the study were current smokers. But a combination of not smoking and being in the highest quintiles for both healthy eating and regular physical activity led to a three-fold decrease in the risk for early AMD.
Only 6 percent of women with the healthiest lifestyles had AMD compared with 18 percent of those with the unhealthiest lifestyles.
In other words, the combination of those factors lowered the risk more than any one factor alone. Why? Probably by increasing protective plant pigments (most notably lutein and zeaxanthin) in the eyes and by lowering blood pressure, oxidative stress and inflammation, suggested Mares.
Interestingly, no link was found between obesity and AMD. Women in the study with the most body fat were more likely to develop early AMD, said Mares, but the trend could be almost completely explained by poor diets and low levels of physical activity.
What you can do
Like all studies, this one has its limitation. By its design, it can show only an association between lifestyle behaviors and AMD, not a cause-and-effect. Furthermore, it involved only women. The results may not be the same for men.
Still, this study (like Mares’ previous one on diet and cataracts) suggests an inexpensive and healthy way of protecting your eyes, particularly if AMD runs in your family.
Mares recommends the following:
- Eat varied and plant-rich diets — ones not too high in fat or sugar.
- Be physically active most days — at least 10 hours a week of light activity (the kind you can sing to) or 8 hours a week of moderate activity (the kind you can talk but not sing to).
- Don’t smoke.
“If we live long enough our eyes degenerate like the rest of our bodies,” said Mares. “But this [study] suggests we could certainly extend the years of good vision.”
You headline, and then say “…overall healthy lifestyle…may significantly reduce their risk”, a cause (healthy lifestyle) leading to an effect (reduced risk).
Later you say “By its design, it can show only an association between lifestyle behaviors and AMD, not a cause-and-effect.”
Perhaps your headline and lead paragraph could be rewritten to reflect the science and not the sizzle.
Accurate science reporting might cause readers to have more respect for and understanding of science, its methods, and interpretation of results.
You’re correct, Stephen, and if you’ve read this column for any length of time, you know that I, too, dislike “sizzle” over science.
I’ve changed my lede to a passive verb.
Love the article. But the proof-readers were asleep again: how do you spell ophthalmology?