Endemic goiter is a common worldwide problem caused by iodine deficiency. People in most developed nations do not have iodine deficiency in their diets. Kwashiorkor and marasmus are both forms of severe malnutrition. Kwashiorkor is caused by a low-protein diet, and marasmus is caused by total calorie deficiency. Most people with a goiter have normal thyroid function. The thyroid becomes hypertrophic in response to a low iodine level, but it is usually able to maintain serum thyroxine (T4) levels.