I answer that, Of all the soul's passions, sorrow is most harmful to the body. The reason of this is because sorrow is repugnant to man's life in respect of the species of its movement, and not merely in respect of its measure or quantity, as is the case with the other passions of the soul.
 Thomas Aquinas, Summa Theologica (1274). copy citation

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Author Thomas Aquinas
Source Summa Theologica
Topic passion sorrow
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17897/pg17897-images.html

Context

“17:22) : "A joyful mind maketh age flourishing: a sorrowful spirit drieth up the bones": and (Prov. 25:20) : "As a moth doth by a garment, and a worm by the wood: so the sadness of a man consumeth the heart": and (Ecclus. 38:19) : "Of sadness cometh death."
I answer that, Of all the soul's passions, sorrow is most harmful to the body. The reason of this is because sorrow is repugnant to man's life in respect of the species of its movement, and not merely in respect of its measure or quantity, as is the case with the other passions of the soul. For man's life consists in a certain movement, which flows from the heart to the other parts of the body: and this movement is befitting to human nature according to a certain fixed measure. Consequently if this movement goes beyond the right measure, it will be repugnant to man's life in respect of the measure of quantity; but not in respect of its specific character: whereas if this movement be hindered in its progress, it will be repugnant to life in respect of its species.
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