A cheerful heart is good medicine, but a crushed spirit dries up the bones. Proverbs 17:22
Medical genetics has discovered epigenomes that turn on/off the expression of genes. Thus in identical twins one may get cancer where the other is spared. When the genes of identical twins are tagged for activity they show nearly identical activity as babies, but later in life they show marked divergence in activity. This change is from epigenes, but what cause epigenes to do this? There are environmental factors that have an effect, but what is surprising is that emotions also produce changes in epigenes. This explains why when a person loses their spouse there is a higher than expected incidence of cancer in the following year. I wonder if this helps explain the placebo effect, associated with any treatment, if one expects a positive out come our emotions cause the production of epigenes that produce the change. Thus the proverb about a cheerful heart is more than a nice statement, it speaks to an underlying biologic mechanism. The opposite emotions also take on new significance in that anger, stress, spite, and hate become avenues for destructive change in our genetics.
All the days of the oppressed are wretched, but the cheerful heart has a continual feast. Proverbs 15:15
So let your mind dwell upon the good things God has given and give thanks.