Thyroid Hormones Linked to Aging

One of the aging theory says that the faster an animal's metabolism, the shorter its life and vice versa.

A study made by Mario Pinto and Rochelle Buffenstein, City College of New York, on rodents with different life span seems to confirm this. The thyroid gland produces hormones implicated in regulating the metabolic rate. "Thyroid hormones are key regulators of metabolism and have been widely implicated to influence longevity," says Pinto.

Thyroxine hormone (T4) is converted to triiodothyronine (T3) in the presence of iodine. "T3 is the active component of T4 and is the key hormone in regulating metabolism," he continued.

"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".

"Significant declines in thyroid hormone correlate well with enhanced maximum lifespan."

Four rodents species with different life spans were compared: house mice (photo above, albino variety used in laboratories), guinea pigs (photo center above), Damara mole-rats (image center bellow) and naked mole-rats (photo bellow).

House mice ( Mus musculus) live to about three and a half years; guinea pigs (Cavia porcellus) live to six years; Damara mole-rats (Coetomys damarensis) to 15 years; and naked mole-rats (Heterocephalus glaber) to 28 years.

The animals chosen from different species were of equivalent ages. For example, two years old naked mole-rats were compared with six months old house mice. The study determined the levels of T3 and T4 for each animal. Comparing T4 levels, they varied greatly, with the shorter-lived species having higher levels of T4 than longer-lived species. The house mice had a double level of T4 than the Damara mole-rats and three times more than that of the naked mole-rats. T3 levels varied greatly between the naked mole-rats and the guinea pigs, but not between any of the other groups.







"These hormone concentration differences correlate with maximum species lifespan and suggest an important regulatory role of thyroid hormone in longevity," Pinto concluded. "However, because T3 levels did not differ significantly among all the groups, further research in this area using larger sample sizes (numbers of rodents in each group) is needed".