July 9, 2008
By Robert H. Shmerling, M.D.
Beth Israel Deaconess Medical Center
Okay, so maybe you've heard this one before: An apple a day keeps the doctor away. I wouldn't have considered this a myth because everyone knows it's not true, right? Well, not so fast. A number of recent studies have actually put this adage to the test, at least indirectly.
Consider the following studies published over the last few years:
In 2007, researchers from Pennsylvania State University found that study subjects who ate an apple before lunch — about 125 calories — consumed 187 fewer calories overall than subjects who didn't eat an apple. Applesauce and apple juice, on the other hand, had no such effect. The researchers suggested that the work of eating the apple or the time it took to eat it somehow made study subjects think they'd eaten more than they had.
Researchers from Cornell University published a study in 2004 in the Journal of Agricultural and Food Chemistry showing that a the flavonoid, quercetin (found primarily in apples, berries and onions) protected the nerve tissue of rats from hydrogen peroxide, a standard oxidative stressor in laboratory preparations. Based on these findings, they theorized that apple consumption might reduce the risk of brain-damaging illnesses, such as Alzheimer's and Parkinson's diseases.
In a 2007 study, researchers in the United Kingdom found that people who ate five apples a week had better lung function and a lower risk of asthma than people who did not eat apples. A prior study suggested the same thing and also linked the beneficial effects of apples to their high concentration of quercetin. Two additional studies have linked apple intake with a lower risk of lung cancer.
A study published in the American Journal of Clinical Nutrition last year linked the high intake of flavonoids (a plant-based nutrient) with lower death rates from cardiovascular disease among postmenopausal women. Of course, apples weren't the only source of flavonoids associated with dodging cardiovascular death. Bran, pears, wine, grapefruit, strawberries and chocolate are also high-flavonoid foods whose intakes were associated with lower cardiovascular disease and/or death rates in this study.
According to a 2006 study, apple juice appeared to "rescue" brain function in mice with Alzheimer's-like disease or with nutritionally deficient diets. In addition to performing better in a maze after the addition of apple juice to their diets, a brain chemical called acetylcholine rose to normal.
Low levels of acetylcholine are associated with Alzheimer's disease in humans. The amount of apple juice these animals consumed was equivalent to two 8-ounce glasses or two to three apples a day for humans. By the way, this study was sponsored by the U.S. Apple Association and the Apple Products Research & Education Council
Considering the findings of these studies, is it time to make apples a bigger part of your diet? Sure, if you like apples. But I don't think we have enough hard evidence to completely buy into the "apple cure" just yet. Some of this research is based on animals, which we know does not always apply directly to humans.
And it's notoriously difficult to perform studies of dietary intake and link them to specific health outcomes when there are so many variables to consider.
For example, when compared with people who don't like apples, maybe apple-eaters have other healthy behaviors, such as exercise, that lower their risk of heart or lung disease.
Apples may be even better for you than previously appreciated. They are a healthy food choice, especially if eaten instead of less nutritious snacks. But even if apples can't keep the doctor away, eating more apples are unlikely to cause you harm.
Regardless of how you feel about apples, this is a good example of how some "myths" are just waiting to be transformed into fact. Good research and an open mind is all that lies between the apple-a-day myth and "the next big thing" in healthy diets.
Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School.
He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.
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