The thyroid gland is crucial to normal body function. Its main functions are control of cellular metabolism ; maintenance of normal brain /neurological function; supporting the pumping effect of the heart; normal remodelling of bone. It also affects menstrual cycles and fertility; mood and cognitive function; and has a role in the activation of all other hormones.
Hypothyroidism (underactive thyroid) is common in midlife, especially in women; see below for diagnosis and treatment.
Fatigue: weight gain; reduced basal body temperature cold intolerance constipation: fluid retention, puffy eyes; dry skin: loss of hair on outer third of eyebrows: accelerated aging; depression, loss of enjoyment, irritability; decreased focus foggy thinking, poor memory; headaches, joint and muscle aches & pains palpitations; reduced stamina: slow or diminished reflexes: lipid disorders increased risk of heart disease. (there is a 260% increase in the rate of heart disease in subclinical hypothyroidism hypertension is also associated with hypothyroidism).
Note: Fatigue is common to both hypo-adrenal states and hypothyroidism: with hypothyroidism, fatigue will be improved by heat and exercise; with hypo-adrenalism, fatigue is marked in the morning, and is increased by exercise, and heat/humidity.
Dietary cravings are different for both conditions; in adrenal fatigue, patients tend to crave salt and foods high in fat & protein (“fast foods”); in hypothyroidism cravings are more for sugary foods and caffeine.
Age-related decline, occurring mostly in women in late 40s, early 50s; Autoimmune thyroiditis: Post surgery or radiation for hyperthyroidism or thyroid cancer: Nutritional deficiencies – iodine, selenium chromium, zinc, ferritin, Vit D; Toxicity – exposure to EM radiation, heavy metals or bromides (found in sports drinks); Functional hypothyroidism ( see below), due to estrogen dominance ( oral estrogen increases binding of thyroid blocks thyroid receptors) adrenal fatigue, progesterone excess, or inadequate tissue conversion of T4 to the more active hormone, T3
Thyroid Hormone production is under the control of the Hypothalamic –Pituitary axis; the hypothalamus detects low levels of T4, produces TRH (thyrotrophic release hormone) which stimulates the pituitary to produce TSH (thyroid stimulating hormone) which in turn stimulates the thyroid gland to produce T4 and small amounts of T3.
T3 is the more metabolically active hormone, but only 20% of this hormone is produced in the thyroid gland; 80% is produced in the peripheral tissues by conversion from T4 by the action of the enzyme 5’deiodinase. Adequate levels of trace elements Selenium, Chromium and Zinc are needed for this process. T4 can also be converted to reverse T3 (a metabolically inert isomer of T3 which blocks binding of T3 to cell receptors)
Some labs rely on TSH as an indirect measure of thyroid function: because of the hypothalamic-pituitary feedback loop, a high TSH value correlates with poor thyroid function. However, there is some dispute as to what the ideal range for TSH should be: the American Society of Endocrinology believes that for optimal thyroid function TSH should be below 2.5 ; but some labs accept a TSH of 5.6 as normal. Additionally, some authorities believe that TSH only reflects brain thyroid hormone activity, and is an inaccurate assessment of peripheral thyroid activity; and prefer to rely on measurement of free T4 and free T3 levels.
Thyroid antibodies- TPO can also be measured if values of T4 or T3 are borderline to rule out autoimmune thyroid disorders such as Hashimoto’s Thyroiditis or Graves’ Disease
Reverse T3 can be measured in one lab in Canada, but is rarely requested.
24 Hr urinary thyroid levels can detect subtle deficiencies of thyroid hormones and of selenium.
Functional Hypothyroidism refers to symptoms of hypothyroidism in the setting of normal lab results.
Factors contributing to this can be
- Increased binding of T4 by Thyroid binding globulin. This hormone-protein complex is too large to enter cells and exert the normal metabolic effect. Factors that can increase the percentage of bound thyroid hormone are estrogen dominance; supplementation with only T4 (Synthyroid or Eltroxin)
- Decreased conversion of T4 to T3, or a shift in conversion to rT3 This can occur with a deficiency of selenium, chromium ,zinc
- Problems with attachment of T3 to the receptor sites on cells Receptor sites can be blocked by rT3, bromides( found in sports drinks) or other halogens – eg excess iodine, fluoride, pesticides
- Problems inside the cell interfering with the transport of thyroid hormones – eg heavy metal toxicity, other nutritional deficiencies inc Vit D, ferritin
- Interaction with other hormones – especially true of cortisol; too much cortisol will decrease pituitary production of TSH, decrease receptor sensitivity to T3, decrease conversion of T4 to T3 and increase production of rT3 by interfering with the action of 5’-deiodinase.Cortisol and thyroid hormone act synergistically in normal circumstances; thus low cortisol- as in late stage adrenal fatigue – will also cause symptoms of hypothyroidism.. in fact 80% of persons with adrenal fatigue will have a functional hypothyroidism.
- Too high levels of estrogen – especially oral estrogen replacement, obesity, which increases fat cell production of Estrone, and too much progesterone, will also cause functional hypothyroidism
Conventionally, most patients with hypothyroidism are treated with T4 in the form of Synthyroid or Eltroxin, and will experience initial improvement in their symptoms; however If T4 alone is given, after a while it will stimulate increased production of thyroid binding globulin; thus the fraction of T4 that is available to convert to T3 is diminished and symptoms will recur despite “normal “ levels of TSH: hence it is always advisable to supplement with both T3 and T4.
Usually we will start with a slow release compounded 4:1 mixture of T4 and T3 , then review symptoms and blood work (TSH, freeT4 and freeT3 )after 2 months and adjust accordingly. If the patient’s lab results improve, but symptoms do not – we will look at the sex hormones and adrenal function, check for selenium and other nutritional deficiencies, and lastly, we can check for the presence of heavy metal or other toxicity.
Nutritional supplements for borderline cases may include Selenium, Zinc, Chromium, Zinc, Iodine, Vit D , B12, ,Herbal therapy; Ashwaganda, Guggol.
Iodine is an important factor in the synthesis of thyroid hormones; it accumulates in the thyroid gland and too little or too much may give rise to problems. Deficiency can be checked by means of a 24hr urine challenge test. If deficient, it can be replaced by Iodoral (a mix of iodine and iodide) 12.5 mgs once or twice a day for up to 3 months. If giving in conjunction with thyroid hormone, it is best to start low and go slow, as excess can be associated with palpitations.