Background: The pituitary hormone TSH stimulates the thyroid gland release of the prohormone T4. T4 has a half-life of 7 days and thereby constitutes a hormone depot in the blood. TSH also stimulates the conversion of T4 to the active hormone T3 in the organs of the body. T3 has a half-life of 7 hours. T3 feeds back on the pituitary secretion of TSH. The T4 depot in the blood stream is kept stable through this feedback regulation between T3 and the pituitary production of TSH, even with the short half-life of T3. The feedback effect of T3 on TSH production lingers over six weeks. To evaluate the effect of thyroid hormones in the body, endocrinologists estimate both clinical symptoms and laboratory results.

Overt hypothyroidism exists in 3-4% of middle-aged and older women in Sweden. The prevalence among men may be 5-10 times lower. It is most often (90%) concomitant with autoimmune infiltration of the thyroid gland and is then also called Hashimoto’s Disease. The underlying cause of hypothyroidism may be generic, and a family history supports the diagnosis of hypothyroidism. Subclinical hypothyroidism is the name given to the condition, when a minor increase in TSH production but still within the normal range is required to keep the blood depot of T4 normal. The condition is thought to explain mild symptoms of hypothyroidism and to indicate treatment with T4. Low sensitivities to TSH and T3 are extremely rare conditions.

Symptoms: Slow mental function, longer sleep periods, slow movements, slow reflexes, slow bowl movements, slow heart rate, changed concepts of time, feeling cold “inside”, dry skin, excessive loss of hair, brittle nails, hoarseness, menstrual irregularities, facial puffiness, muscular aches, increased body weight with lower appetite. Symptoms are often observed by relatives rather than by the patient herself. Fatigue is a common symptom. It is a diagnostically challenging symptom, because it occurs in numerous other diseases. Symptoms must be evaluated professionally and in the context of laboratory results.

Diagnosis: Hypothyroidism occurs most often (90%) together with autoimmune infiltration of the thyroid and with presence of specific antibodies in the blood, but many people have specific thyroid antibodies in the blood without having hypothyroidism, and antibodies cannot be used to diagnose hypothyroidism. Thyroid antibodies indicate risk of future hypothyroidism. 

Treatment: When treating hypothyroidism with synthetic T4, the body will automatically create the T3/T4 ratio that is natural to humans. In cows and pigs the T3/T4 ratio is 3-4 times higher than in humans and for that reason some patients prefer treatment with animal thyroid extracts, which will give them a greater T3 effect during hours following intake of the extract. Because of the long-term potential side effects that is not recommendable. If a patient still wants a morning “kick” effect, then that should be achieved by a carefully considered ratio of synthetic T3 to synthetic T4 tablets within the range “natural” to humans. If the T3 effect becomes too high, dangerous side effects on heart and bone structure develop. Hypothyroidism is a lifelong decease, and treatment, once begun, is lifelong. Three to four percent of patients with hypothyroidism also have gluten intolerance and need treatment with a higher dose of T4.


is a disease in which the thyroid gland produces too much thyroid hormone. It has an incidence of 0.27 0/00 in Sweden, and it occurs about four times more frequently in women than in men. It may occur as autonomous T3 production in the thyroid gland.

Symptoms: Abnormally increased production of thyroid hormone may cause increased perspiration, increased appetite with decreasing body weight, increased heart rate, increased body temperature, diarrhea, shorter sleep periods, fast mental function, restlessness, aggressiveness, irritability, depression. Patients will often appreciate a higher energy level and higher work capacity. In patients above the age of 65 to 70 years the condition may be “silent” except for irregular heart rate. It may cause heart insufficiency and loss of bone mass. Like hypothyroidism it has a genetic cause may occur with coincidentally increased levels of autoantibodies to thyroid enzymes (Hashimoto Disease). The most common appearance of hyperthyroidism in Sweden is usage of too high a dose of T4.

Diagnosis: Hyperthyroidism is diagnosed by measuring T3 and T4 in blood.

Treatment: Hyperthyroidism may be effectively treated in three different ways, with oral medications, by surgery, or by a drink of radioactive iodine. All three treatment modalities may result in low thyroid function and in that case require lifelong treatment with oral T4. Intake of radioactive iodine is the preferred permanent treatment, because it does not have side effects and often does not require additional lifelong treatment.
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