Mesothelioma and General Health

The thyroid itself is regulated by another gland that is located in the brain, called the pituitary. In turn, the pituitary is regulated in part by the thyroid (via a “feedback” effect of thyroid hormone on the pituitary gland) and by another gland called the hypothalamus. The hypothalamus releases a hormone called thyrotropin releasing hormone (TRH), which sends a signal to the pituitary to release thyroid stimulating hormone (TSH). In turn, TSH sends a signal to the thyroid to release thyroid hormones. If a disruption occurs at any of these levels, a defect in thyroid hormone production may result in a deficiency of thyroid hormone (hypothyroidism).

• Hypothalamus – TRH

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• Pituitary- TSH

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• Thyroid- T4 and T3

The rate of thyroid hormone production is controlled by the pituitary gland. If there is an insufficient amount of thyroid hormone circulating in the body to allow for normal functioning, the release of TSH is increased by the pituitary gland in an attempt to stimulate more thyroid hormone production. In contrast, when there is an excessive amount of circulating thyroid hormone, TSH levels fall as the pituitary attempts to decrease the production of thyroid hormone. In persons with hypothyroidism, there is a persistent low level of circulating thyroid hormones.

Subclinical hypothyroidism occurs when thyrotropin (TSH) levels are elevated but thyroxine (T4) and triiodothyronine (T3) levels are normal. Prevalence estimates range 3–8%, increasing with age; incidence is more common in women than in men.[30] In primary hypothyroidism, TSH levels are high and T4 and T3 levels are low. TSH usually increases when T4 and T3 levels drop. TSH prompts the thyroid gland to make more hormone. Hypothyroidism is sub-clinical if it has no discernible adverse effect on cellular metabolic rates (and ultimately the body’s organs). The levels of the active hormones will be within the laboratory reference ranges. There is a range of opinion on the biochemical and symptomatic point at which to treat with levothyroxine, the typical treatment for overt hypothyroidism. Reference ranges have been debated as well. The American Association of Clinical Endocrinologists (ACEE) considers 0.45–4.5 mIU/L, with the ranges down to 0.1 and up to 10 mIU/L requiring monitoring but not necessarily treatment.[31] There is always the risk of overtreatment and hyperthyroidism. Some studies have suggested that subclinical hypothyroidism does not need to be treated. A meta-analysis by the Cochrane Collaboration found no benefit of thyroid hormone replacement except “some parameters of lipid profiles and left ventricular function.”A more recent metanalysis looking into whether subclinical hypothyroidism may increase the risk of cardiovascular disease, as has been previously suggested,[33] found a possible modest increase and suggested further studies be undertaken with coronary heart disease as an end point “before current recommendations are updated