On the contrary, The Philosopher says (Ethic. x, 4) that “pleasure perfects action,” whereas on the other hand, “sorrow hinders it” (Ethic. x, 5).

I answer that, As stated above (A. 2), sorrow at times does not depress or consume the soul, so as to shut out all movement, internal or external; but certain movements are sometimes caused by sorrow itself.  Accordingly action stands in a twofold relation to sorrow.  First, as being the object of sorrow:  and thus sorrow hinders any action:  for we never do that which we do with sorrow, so well as that which we do with pleasure, or without sorrow.  The reason for this is that the will is the cause of human actions:  and consequently when we do something that gives pain, the action must of necessity be weakened in consequence.  Secondly, action stands in relation to sorrow, as to its principle and cause:  and such action must needs be improved by sorrow:  thus the more one sorrows on account of a certain thing, the more one strives to shake off sorrow, provided there is a hope of shaking it off:  otherwise no movement or action would result from that sorrow.

From what has been said the replies to the objections are evident.
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FOURTH ARTICLE [I-II, Q. 37, Art. 4]

Whether Sorrow Is More Harmful to the Body Than the Other Passions of the Soul?

Objection 1:  It would seem that sorrow is not most harmful to the body.  For sorrow has a spiritual existence in the soul.  But those things which have only a spiritual existence do not cause a transmutation in the body:  as is evident with regard to the images of colors, which images are in the air and do not give color to bodies.  Therefore sorrow is not harmful to the body.

Obj. 2:  Further if it be harmful to the body, this can only be due to its having a bodily transmutation in conjunction with it.  But bodily transmutation takes place in all the passions of the soul, as stated above (Q. 22, AA. 1, 3).  Therefore sorrow is not more harmful to the body than the other passions of the soul.

Obj. 3:  Further, the Philosopher says (Ethic. vii, 3) that “anger and desire drive some to madness”:  which seems to be a very great harm, since reason is the most excellent thing in man.  Moreover, despair seems to be more harmful than sorrow; for it is the cause of sorrow.  Therefore sorrow is not more harmful to the body than the other passions of the soul.

On the contrary, It is written (Prov. 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.”