Perhaps, when the sentence says that hygiene is 2/3 of health it means that dealing with your body and your adrenal glands meaning the adrenal gland consists of adrenal cortex and adrenal medulla. So the adrenal cortex helps produces hormones that are important to life such as regulating metabolism and helps your body respond to stress, So it helps you not get diseases if you have healthy hygiene. Hoped that helped!!