"An apple a day keeps the doctor away” (or, to hedge bets a little, “An apple a day helps to keep the doctor away") has been promoted by American apple organizations since almost 1900. The promotions usually occurred during Apple Day/Week/Month in October.
The rhyme “Eat an apple on going to bed, and you’ll keep the doctor from earning his bread” was popular in England and is first cited in print in 1866 (from Pembrokeshire, Wales). The modern rhyme of “An apple a day keeps the doctor away” is cited in England by 1893.
A popular joke version (with variations from at least 1903) is “An apple a day keeps the doctor away, but an onion a day keeps everybody away.” “Why are doctors so afraid of apples, anyway?” is another jocular response.
(Oxford English Dictionary)
an apple a day keeps the doctor away and similar phrases.
1866 N. & Q. 24 Feb. 153/2 A Pembrokeshire proverb. Eat an apple on going to bed, And you’ll keep the doctor from earning his bread.
1898 19th Cent. Apr. 644 There is no food so palatable, so wholesome, as fruit: ‘An apple a day, no doctor to pay.’
1899 Youth’s Compan. 10 Aug. 398/3 An apple a day sends the doctor away.
1913 E. M. WRIGHT Rustic Speech xiv. 238 Ait a happle avore gwain to bed, An’ you’ll make the doctor beg his bread (Dev[on]); or as the more popular version runs: An apple a day Keeps the doctor away.
1922 S. LEWIS Babbit (1961) i. 13 Of course I eat an apple every eveningan apple a day keeps the doctor away.
1934 Washington Post 30 Oct. 4/4 Testimonials to the truthfulness of that old saw about an apple a day keeping the doctor away.
2006 Lincs. Echo (Nexis) 29 Aug. 13 An apple a day may keep the doctor away, but a glass of cider a day is even better for your health.
24 February 1866, Notes and Queries, pg. 153:
A PEMBROKESHIRE PROVERB.—
“Eat an apple on going to bed,
And you’ll keep the doctor from earning his bread.”
JOHN PAVIN PHILLIPS.
3 August 1870, Pomeroy’s Democrat (Chicago, IL), “Agricultural Noted from Central New York “ (Utica), pg. 3:
Who plants an apple tree makes provision against life’s rainy days, against loss of health, misfortuna in business and old age; also, you will keep the doctor away from your children and yourself.
February 1874, The Dublin University Magazine, ‘The Folk-Lore of British Plants,” pg. 194:
“Eat an apple on going to bed,
And you’ll keep the doctor from earning his bread,”
is a Pembrokeshire proverb, and a somewhat similar saying is current in many other places.
Glossary of Words in Use in Cornwall:
By Miss M. A. Courtney
By Thomas Q. Couch
London: Published for the English Dialect Society by Trubner & Co.
“Eat an apple going to bed,
Make the doctor beg his bread”
Whence they come and how they are cooked
By Anne Walbank Buckland
London: Ward & Downey
“An apple a day keeps the doctor away,” says the proverb, and there can be no doubt that in temperate climes the apple, from its excellent hygienic and keeping qualities, ranks first in usefulness.
December 1893, The Chautauquan, pg. 345:
A not too ancient English maxim runs:
“To eat an apple going to bed
The doctor then must beg his bread.”
Making of America
21 May 1898, The Living Age, pg. 547:
“An apple a day, no doctor to pay.”
22 December 1900, Gardeners’ Chronicle, pg. 457, col. 3:
AN Apple a day
Sends the doctor away.
Apple in the morning,
Roast Apple at night,
Starved the doctor outright.
Eat an Apple going to bed,
Knock the doctor on the head.
23 December 1900, Anaconda (MT) Standard, pg. 23, col. 5:
From the Pall Mall Gazette.
An old saying has it that “an apple a day keeps the doctor away,” and if so a bottle of good cider taken regularly at luncheon should make the medical profession superfluous.
21 August 1905, Washington (DC) Times, “Fruit in the Menu,” pg. 7, col. 3:
Less bacon and more fruit during the hot weather is a good rule, and the old saying, “An apple a day keeps the doctor away” has, like many more old sayings, a good deal of common sense and wisdom in its jingle.