Low T levels can alter weight, appetite, sleep patterns, body temperature, sex drive, and a variety of other physical, mental, and emotional characteristics. There are three types of hypothyroidism. The most common is primary hypothyroidism, in which the thyroid doesn't produce an adequate amount of T . Tertiary hypothyroidism results from a malfunction of the hypothalamus, the part of the brain that controls the endocrine system. Drug-induced hypothyroidism, an adverse reaction to medication, occurs in two of every 10,000 people, but rarely causes severe hypothyroidism.
Hypothyroidism is at least twice as common in women as it is in men.
Although hypothyroidism is most common in women who are middle-aged or older, the disease can occur at any age. Treatment within the first few months of life can prevent mental retardation and physical abnormalities. Older children who develop hypothyroidism suddenly stop growing. Factors that increase a person's risk of developing hypothyroidism include age, weight, and medical history. Obesity also increases risk.