The daily apple eaters in the study were more likely to successfully avoid prescription medication use than people who did not eat apples.
The study tells us that the "an apple a day keeps the doctor away" aphorism was coined in 1913 but was based on the original form with a different rhyme, some 149 years ago in Wales: "Eat an apple on going to bed and you'll keep the doctor from earning his bread," went the proverb in Pembrokeshire.
The University of Michigan School of Nursing researchers in Ann Arbor believe giving such medical proverbs an empirical evaluation "may allow us to profit from the wisdom of our predecessors."
For the study's measure of keeping the doctor away, Matthew Davis, PhD, and co-authors evaluated an outcome of no more than one visit a year to the doctor as a means of investigating the proverb's success in daily apple eaters compared with non-apple eaters.
So did a daily apple succeed in keeping the doctor away? No, it did not. There was no statistically meaningful difference in visits to the doctor for daily apple eaters in the analysis. But the study did find that an apple a day kept the pharmacist away.
'Avoiding the use of health care services'
When socio-demographic and health-related characteristics such as education and smoking were taken into account, daily apple eating was not associated with successfully keeping to a maximum of one self-reported doctor visit a year.
Of the 8,399 participants who answered a questionnaire to recall their dietary intakes, 9% (753) were apple eaters and the remainder, 7,646, were non-apple eaters.
The apple eaters showed higher educational attainment, were more likely to be from a racial or ethnic minority, and were less likely to smoke. The data for the analysis came from the National Health and Nutrition Examination Survey conducted during 2007-08 and 2009-10.
"While the direction of the associations we observed supports the superiority of apple eaters over non-apple eaters at avoiding the use of health care services, these differences largely lacked statistical significance," say the authors after accounting for the differences in apple-eaters that - beyond the effects of the apple-eating itself - could have explained why they used health care services less.
An apple a day means one of at least 7 cm diameter
To analyze apple-eating against visits to the doctor, the researchers compared daily apple eaters with non-apple eaters. An apple a day counted if the participants answered that they had at least 149 g of raw apple.
Eating less than this amount counted as no daily apple-eating, and apple consumption based purely on juices or sauces was also excluded. The study also looked for any response to increasing the amount of daily apple-eating by comparing doctor visits from people who ate no apples with those who ate one small apple, one medium apple or one large apple daily.
The analysis shows no relationship between apple "dose" and the likelihood of keeping the doctor away in terms of "avoiding health care services." Except, found the authors, for avoidance of prescription medications.
The study found that apple eaters were more likely to keep the doctor away, but this was before adjusting for the socio-demographic and health characteristics of the survey respondents - 39.0% of apple-eaters avoided more than one yearly doctor visit, compared with 33.9% of non-apple eaters.
The daily apple eaters were also more likely to successfully avoid prescription medication use (47.7% versus 41.8%) - and this difference survived statistical analysis.
The association between eating an apple a day and keeping the pharmacist away, then, was a statistically significant finding, whereas keeping the doctor away failed to hold true.
Nor did the proverb show any effect in an analysis of overnight hospital stays or mental health visits - there was no difference for apple eaters in the likelihood of keeping either of these two away.
The overall conclusion of this study was that only one finding supported the long-standing wisdom. Apple eaters "were somewhat more likely to avoid prescription medication use than non-apple eaters."
The authors say in their final analysis that promotion of apple consumption may have only "limited benefit" in reducing national health care spending, adding:
"In the age of evidence-based assertions, however, there may be merit to saying, 'An apple a day keeps the pharmacist away.'"