Cheerfulness is, in the first place, the best promoter of health. Repinings, and secret murmurs of heart, give imperceptible strokes to those delicate fibres of which the vital parts are composed, and wear out the machine insensibly; not to mention those violent ferments which they stir up in the blood, and those irregular disturbed motions which they raise in the animal spirits.

Joseph Addison (1672-1719) English essayist, poet, statesman

Essay (1712-05-24), The Spectator, No. 387
    (Source)