Herein, the
authors show, using wild-type and the Pax8 ablated model of hypothyroidism in
mice, that hyperthyroidism and severe hypothyroidism are associated with an
overall unhealthy status and shorter lifespan.
Mild
hypothyroid Pax8 +/- mice were heavier and displayed insulin resistance,
hepatic steatosis and increased prevalence of liver cancer yet had normal
lifespan.
TSH
stimulates the production of T4 and T3 in the thyroid gland, which in turn
inhibit both TRH and TSH synthesis when THs reach the hypothalamus and
hypophysis, respectively.
Greater life
expectancy has been associated with reduced circulating levels of T4, T3,
and/or high TSH levels in both animal models and humans.
In this
line, the Laron, Ames and Snell dwarf mice, which have reduced GH signalling
and reduced circulating TH levels, exhibit a consistent exceptional lifespan as
well as other metabolic alterations such as enhanced hepatic insulin
sensitivity.
Both rodents
and humans under calorie restriction, which comprises a variety of nutritional
interventions with several beneficial effects including extended longevity,
exhibit reduced circulating T3 levels and/or high TSH levels.
Likewise,
nonagenarians from families with exceptional long lifespans, as well as their
descendants, have been reported to exhibit increased TSH levels and/or
decreased circulating T3 levels.
The
Martin-Montalvo research team concluded, "In 1908 Dr. Max Rubner proposed
the rate of living theory of aging and longevity, postulating that species with
a low metabolic rate would have increased life expectancy when compared to
species with a higher metabolic rate.
In this
line, restricted levels of THs, which control the metabolic rate, have been
associated with increased longevity as well as metabolic fitness.
From
source: https://www.news-medical.net
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