AKB0048 (anime) and AKB49 (manga) are based on popular Japanese idol group AKB48.
What were the first manga and anime based on real idols instead of fictional characters?
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As far as I know, 『アイドルコミックス・実録まんが岡田有希子』 Idol Comics: Documentary Manga Yukiko Okada (published by Gakken in 1984) featuring the story of Yukiko Okada's early life until her debut could be the first of its kind.
Update: Idol Comics was a series of manga based on the real lives of not only idols, but also famous baseball players and pro wrestlers ("idol" in a wider sense). As far as I can find on Amazon.co.jp, it appears that the first volumes came out in January, 1983. One of the volumes featured 堀ちえみ Chiemi Hori (idol born in 1967, debut 1982), so that would make this the earliest one I can find. The other three volumes that came out in the same month featured Tatsunori Hara (baseball player), Daisuke Araki (baseball player), and Tiger Mask (pro wrestler).
As for the anime, 『ピンク・レディー物語 栄光の天使たち』Pink Lady Monogatari: Eiko no Tenshitachi (TV anime aired from 1978 to 1979) featuring Pink Lady would most likely be the first. There seems to be some made-up episodes inserted (like intensive training to dance with their limbs bound), but most of what was depicted was based on real-life stories.