The proverb “An apple a day keeps the doctor away” is very common in the English language today but it originated —at the latest— in the 19th century.
A variant of the phrase, "Eat an apple on going to bed, and you'll keep the doctor from earning his bread" was recognised as a Pembrokeshire saying in the 1866 edition of the Welsh magazine Notes and Queries.
The modern form of the proverb first appeared in Rustic Speech and Folk-Lore (1913), by the English linguist Elizabeth Mary Wright.
But what is the science behind the proverb? Is it really true that eating an apple a day can prevent illness?
Health benefits of apples
Apples are rich in several kinds of antioxidants.
Antioxidants are substances that prevent damage to the cells caused by free radicals. Free radicals are atoms, molecules, or ions that have at least one unpaired valence electron. They are formed naturally by your body during exercise and in processes such as inflammatory responses, and during normal metabolic activity in the cells such as converting food into energy. They can also come from a variety of environmental sources, such as cigarette smoke, air pollution, industrial chemicals, radiation exposure, and sunlight.
This means that free radicals can’t be utterly kept from developing in the body (they’re actually believed to play a significant role in aging). But it’s good to keep them under control to prevent oxidative stress —an imbalance between free radicals and antioxidants that can trigger cell and tissue damage.
Long-term oxidative stress deteriorates the body’s cells, proteins, and DNA. This is why it’s been linked to cardiovascular conditions (high blood pressure, atherosclerosis, vasculitis, strokes), neurodegenerative disorders like Alzheimer’s disease and Parkinson’s disease (when oxidative stress kills brain cells), cancer, inflammatory conditions like arthritis and asthma, diabetes, lupus, gastric ulcers, etc.
Hence the potential importance of consuming antioxidants. Antioxidants “donate” electrons to free radicals to help minimize the harmful instability of free radicals, and eventually reduce oxidative stress.
In the laboratory, apples have been found to have very strong antioxidant activity, inhibit cancer cell proliferation, decrease lipid oxidation, decrease the risk of certain types of cancer, and lower cholesterol levels and the risk of cardiovascular disease. This is one reason why diets high in vegetables and fruits, which are good sources of antioxidants and fiber, are considered to be healthier than diets low in these foods.
Apples also contain pectin, a natural fiber found in plants that may help lower cholesterol and regulate the beneficial bacteria in the gut, something that is promising for new methods of prevention and solutions for inflammation-related weight gain or obesity.
Certainly, the fiber content of apples puts them low on the glycaemic index (GI), a food rating system that measures how much some meals can affect your blood sugar levels. Because apples do not alter the body’s blood sugar levels so quickly, they’re believed to help with weight and diabetes management by enhancing the body’s insulin sensitivity.
Furthermore, apples are an excellent source of:
- Polyphenols, a kind of micronutrient in plants that passes to humans through apples and other fruits and vegetables. There is a specific type of polyphenols called flavonoids, and apples contain the flavonoid called quercetin, which is related to a lower risk of various chronic diseases.
- Vitamin C, an acid that boosts the immune system and promotes the formation of collagen —the main structural protein of connective tissue, essential for wound healing and tissue repair. Vitamin C also benefits the absorption of iron, a mineral involved in the fabrication of hemoglobin, the protein in the red blood cells that carry oxygen from the lungs to the rest of the body and organs.
- Vitamin A, which improves your vision, your immune system, and your body’s antioxidant activity. It also plays a role in cell division, growth, and reproduction.
- Vitamin B1 or thiamine, a water-soluble vitamin that is vital for converting food into energy and keeping a proper nerve function. In fact, a severe thiamine deficiency can cause an illness called beriberi, which affects both the nervous system and the cardiovascular system.
- Riboflavin, also known as Vitamin B2, is necessary for energy metabolism, cellular respiration, skin development, brain function, antibody production, and other processes.
- Vitamin B6, a vitamin that contributes to energy production through metabolism and creates essential neurotransmitters like serotonin and dopamine. Vitamin B6 also ensures proper brain development during pregnancy and infancy.
In 2014, health services researcher Matthew A. Davis, of the Dartmouth Institute for Health Policy and Clinical Practice, led an investigation into the relationship between apple eating and visits to the doctor.
He examined the daily diet of 8,728 American adults from the 2007-2008 and 2009-2010 National Health and Nutrition Examination dietary recall survey and separated them between daily apple eaters and non-apple eaters.
The researchers identified 753 adults who usually ate at least one small apple (143 gr) per day. This group made up around 9 percent of the study participants.
In the crude analysis, Matthew A. Davis and his team found out that 39 percent of apple eaters did not report any visit to the physician and/or prescription medications in the last year. In comparison, 33.9 percent of non-apple eaters “kept the doctor away”.
After adjusting for sociodemographic and health-related characteristics, however, the association between apple eating and doctor visits was no longer statistically significant. Although, in the adjusted analysis, apple eaters did remain "marginally more successful" at avoiding prescription medications.
Some of the other factors involved in the frequency of physician visits and hospital stays included whether a participant had health insurance or not (meaning they visited the doctor less) and whether they were overweight or had other health conditions.
The researchers concluded that the "evidence does not support that an apple a day keeps the doctor away; however, the small fraction of US adults who eat an apple a day do appear to use fewer prescription medications."
In general, though, apple eaters were also more likely to make other healthy choices, such as not smoking and eating a more nutritious diet overall. This suggests that eating apples by themselves does not help avoid physician visits, but they may contribute to an individual’s overall health if combined with other beneficial decisions.
In conclusion, an apple a day may not necessarily keep the doctor away by itself, but it is certainly part of a healthy diet — which includes a high amount of fruits and vegetables, along with other healthy practices, such as exercise.