I have begun to be somewhat merry because I have been told that that is good for one’s health. ~Voltaire

Ayant fait réflexion, depuis quelques années, qu’on ne gagnoit rien à être bon homme, je me suis mis à être un peu gai, parce qu’on m’a dit que cela est bon pour la santé.

This is translated by Barbara Bray and Helen R. Lane in their 1979 translation of Orieux’s Voltaire, as follows:

It is true that, on having reflected for some years now that scarcely anything was to be gained by being so, I have begun to be somewhat merry because I have been told that that is good for one’s health. (Letter to the Abbé Trublet, April 17, 1761).