An apple a day keeps the doctor away
It isn't often that I get the opportunity to list Wales as the source of a commonplace English phrase. There's a fair chance that this little maxim originated there as the earliest known example of its use in print makes that claim. The February 1866 edition of Notes and Queries magazine includes this:
"A Pembrokeshire proverb. Eat an apple on going to bed, And you'll keep the doctor from earning his bread."
A number of variants of the rhyme were in circulation around the turn of the 20th century. In 1913, Elizabeth Wright recorded a Devonian dialect version and also the first known mention of the version we use now, in Rustic Speech and Folk-lore:
"Ait a happle avore gwain to bed, An' you'll make the doctor beg his bread; or as the more popular version runs: An apple a day Keeps the doctor away."
Apples have a good claim to promote health. They contain Vitamin C, which aids the immune system, and phenols, which reduce cholesterol. They also reduce tooth decay by cleaning one's teeth and killing off bacteria. It has also been suggested by Cornell University researchers that the quercetin found in apples protects brain cells against neuro-degenerative disorders like Alzheimer's Disease.
Apples may be good for us but it wasn't their precise medicinal properties that were being exalted when this phrase was coined. In Old English the word apple was used to describe any round fruit that grew on a tree. Adam and Eve's forbidden fruit, which they ate in the Garden of Eden, is often described as an apple but, in the 1611 King James Version of the Bible, it is just called 'a fruit'.
See also: the List of Proverbs.