No, an apple a day does not appear to keep the doctor away. But, a new study semi-seriously suggests, it may keep the pharmacist away. The study serves as an instructive and humorous way to look at the perpetually thorny problem of how to best understand and make use of findings from observational studies. As this new paper makes clear, the limitations of observational studies are quite considerable, but that does not mean that they are completely worthless.
Although apples have long been considered a healthy snack, whether eating apples actually reduces healthcare use has not been assessed until now. In a paper published in JAMA Internal Medicine researchers examined the association between healthcare utilization and apple consumption in more than 8,000 adults participating in the National Health and Nutrition Examination Survey.
At first glance apples appeared to be related to significant benefits. Apple eaters, defined as those who ate at least one small apple each day, were more likely to "keep the doctor away" (defined as no more than 1 doctor visit in the past year): 39% versus 33.9% for non-apple eaters. Apple eaters were also less likely to take prescription drugs: 47.7% vs 41.8%. But the researchers found no difference between the groups in overnight hospital stays or in visits to a mental health professional.
But the results were less robust after the researchers adjusted for sociodemographic and health-related factors. Disproving the adage about an apple a day, the primary endpoint-- the reduction in the number of doctor visits-- was no longer statistically significant. However, the finding that apple eaters avoided taking prescription drugs remained marginally significant.
Apple eaters constituted only 9% of the group studied, which in the US works out to 19.3 million adults who are apple eaters and 207.2 million adults who are not. The authors calculated, though it is unclear whether they were entirely serious, that universal apple consumption among US adults would result in a $47 billion reduction in prescriptions at a cost of $28 billion in apples.
The authors acknowledged the major limitation of their study: "Apple eaters were, in fact, measurably different from non–apple eaters and would be expected to differ in other, unmeasured ways. Specifically, individuals who eat apples may be more health conscious and otherwise healthier, which could entirely explain the associations we observed."
In an editorial note, JAMA Internal Medicine editor Rita Redberg informs readers that the article is part of the journal's "first April Fool’s issue." In an email Redberg said that she "did not ask the readers to discount the findings." Instead, she said, the paper shows that "a study could be scientifically rigorous and still have some humor or light side, as this one did."
