It is the Holy Grail of health research, discovering the key to help people live longer.
Now scientists believe they may be one step closer.
A team at Yale School of Medicine have identified a hormone, produced by the thymus glad, extends lifespan by 40 per cent.
Their findings reveal increased levels of the hormone, known as FGF21, protects the immune system against the ravages of age.
Researchers said the study could have implications in the future for improving immune function in the elderly, for obesity, and for diseases such as cancer and type 2 diabetes.
When it is functioning normally, the thymus produces new T cells for the immune system.
But with age, the gland becomes fatty and loses its ability to produce the vital cells.
This loss of new T cells in the body is one cause of increased risk of infections and certain cancers in the elderly.
Researchers led by Vishwa Deep Dixit, professor of comparative medicine and immunobiology at Yale, studied transgenic mice with elevated levels of FGF21.
They blocked the gene’s function, before studying the impact of decreasing levels of FGF21 on the immune system.
Their results showed that increasing the level of FGF21 in old mice protected the thymus from age-related fatty degeneration and increased the ability of the thymus to produce new T cells.
Meanwhile, FGF21 deficiency accelerated the degeneration of the thymus in old mice.
Professor Dixit said: ‘We found that FGF21 levels in thymic epithelial cells is several fold higher than in the liver, therefore FGF21 acts within the thymus to promote T cell production.
‘Elevating the levels of FGF21 in the elderly or in cancer patients who undergo bone marrow transplantation may be an additional strategy to increase T cell production, and thus bolster immune function.’
The hormone, produced by the thymus glad, extends lifespan by 40 per cent. Their findings reveal increased levels of the hormone, known as FGF21, protects the immune system against the ravages of age
Professor Dixit added that FGF21 is produced in the liver as an endocrine hormone.
Its levels increase when calories are restricted to allow fats to be burned when glucose levels are low.
FGF21 is a metabolic hormone that improves insulin sensitivity and also induces weight loss.
Therefore it is being studied for its therapeutic effects in type 2 diabetes and obesity.
Professor Dixit said future studies will focus on understanding how FGF21 protects the thymus from aging, and whether elevating FGF21 through the use of drugs, could extend human lifespan and lower the incidence of disease caused by age-related loss of immune function.
He added: ‘We will also look to developing a way to mimic calorie restriction to enhance immune function without actually reducing calorie intake.’
The study was published in the Proceedings of the National Academy of Sciences.