The thyroid may play an important role in longevity, with longer-lived rodents showing significantly lower levels of a thyroid hormone that speeds metabolism, a new study has found.//

The study further strengthens the theory that the faster an animal’s metabolism, the shorter its life, and vice versa, said Mario Pinto, the study’s lead author. The thyroid releases hormones that regulate metabolic rate.

“Thyroid hormones are key regulators of metabolism and have been widely implicated to influence longevity,” the authors wrote. Pinto will present the study “Differential thyroid hormone activity in rodents with different life spans” at a poster session Oct. 9 at Comparative Physiology 2006: Integrating Diversity. The study was carried out by Pinto and Rochelle Buffenstein, City College of New York.

Thyroid key to metabolic rate

The thyroid gland produces thyroxine (T4) which converts to triiodothyronine (T3) in the presence of iodine. T3 is the active component of T4 and is the key hormone in regulating metabolism, Pinto said. When an animal becomes cold, for example, its body converts T4 to T3 to speed metabolism and warm the body, he explained.

'Mice strains that exhibit extended longevity tend to have lower thyroid hormone concentrations than shorter living strains,' the authors wrote. 'Significant declines in thyroid hormone correlate well with enhanced maximum lifespan.'

The study compared the levels of these thyroid hormones among four groups of rodents with different life spans: mice, guinea pigs, Damara mole-rats and naked mole-rats. Mice live to about three and a half years; guinea pigs live to six years; Damara mole-rats to 15 years; and naked mole-rats to 28 years.

The animals were of different ages, but at comparable points in their life spans. For example, the mole-rats, which live 28 years, were two years old. The mice, which live about 3.5 years, were six months old. The s
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