This is caused by our wrong way of life. Diabetes is similar. We become diabetic because we don't use the energy gained from eating but continue taking in food and our body becomes saturated. This can lead to diabetes. The cause of disease is quite often bad eating, sleeping or working habits.
Stimulation is also important for our health.
We study God's word in order to know which way we should go. We also study God's words to receive stimulation. Stimulation is needed if our internal organs are to work properly. Thus in order to maintain good health, the body must be given proper stimulation. This also applies to our spiritual health.