Scientists are experimenting with a life-extending hormone that bolsters the body’s immune system and lowers the chance of contracting diseases caused by age-related loss of immune function.

By increasing the level of the hormone FGF21 researchers from Yale School of Medicine found the lifespan of mice was increased by 40%. However, they believe the study has implications for improving immune function in the elderly, for tackling obesity and for treating diseases such as cancer and type-2 diabetes.

Increased levels of FGF21 protects the thymus gland and allows it to produce new T cells. Normally, with age, the thymus becomes fatty and loses its ability to make T cells, which can lead to increased risk of infections and the contraction of certain cancers.

“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,” said lead researcher Vishwa Deep Dixit.

“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.”

FGF21 is produced in the liver as an endocrine hormone. Its levels naturally increase when we cut back on calories and allow fats to be burned as our glucose levels fall.

However, following the initial tests on mice, the researchers will now look at whether pharmaceutical products that increase the levels of FGF21 might extend human life.

The hormone is also being studied for its medicinal effects in treating type-2 diabetes and tackling obesity.

Specifically, Dixit noted how research will now focus on using the findings from this study to stop the harmful side effects associated with obesity while avoiding the need for patients to lower their calorie intake.

Dixit explained: “We will also look to developing a way to mimic calorie restriction to enhance immune function without actually reducing caloric intake.”

The researcher’s findings are available online in the Proceedings of the National Academy of Sciences.