There is ample evidence that good health has a favorable effect on personality while poor health, whether physical or psychosomatic in origin and whether real or imaginary, has a damaging effect. Many personality changes result from poor health condition and persist even after the illness has been cured or its severity lessened. This is especially true during childhood, when personality is in its formative stage. In fact, many personality disturbances in adolescents and adults trace their origin to illness during the early childhood years.
Regardless of the nature of illness or the age of person experiencing it, any illness reduces the scope of person’s world. It encourages him to be egocentric and selfish, it causes frustration which may make the person aggressive and cantankerous or withdrawn, it leads the heightened emotionally, and it makes the person feel martyred. In older people, illness often encourages regression to an earlier period of their lives when they were healthier and happier.
Even tiredness, caused by poor health, overexertion, frustration, or boredom with one’s role in life, lead to personality changes which often become persistent if the conditions responsible for the tiredness persist. Constant tiredness may turn a happy, well-adjusted person into an unhappy, poorly adjusted one.
A number of studies show how marked an effect certain illness have on personality. Persons suffering from diabetes experience tension and anxiety which cause frustration when they try to conform to the demands of their social environments. As a result of frustration, they become aggressive, often turning their aggressions outward on others.
Some of the predisposition to irritability and crabbiness in old age may be traced to changes in the blood sugar level caused by the body’s inability to withdraw glucose from the bloodstream and store it in tissues which have been damaged by the aging process.
Since illness in old age has such damaging effects on personality, it has been suggested that one of the best preparations for old age is health measures designed to prevent chronic and progressive diseases which impair the efficiency and happiness of the elderly and, as such, contribute to unfavorable personality changes. This suggestion could well be applied to all ages. Preventing illness and keeping the person in a state of good health would do much to ensure the development of a wholesome personality, good personal and social adjustments, and happiness.