It's been known for a while that severely restricting food intake can increase lifespan in some animals dramatically - but few people have been willing to take that step.
Now, though, researchers have identified a 'starvation hormone' that has the same effect on mice, without the need for calorie restriction.
"In our study, we found transgenic mice that produced more of the hormone fibroblast growth factor-21 (FGF21) got the benefits of dieting without having to limit their food intake," says professor Steven Kliewer of UT Southwestern Medical Center.
"Male mice that overproduced the hormone had about a 30 percent increase in average life span and female mice had about a 40 percent increase in average life span."
When it comes to maximum life expectancy, the data isn't even all in yet: while none of the untreated mice lived longer than about three years, some of the female mice that overproduced FGF21 will soon reach the age of four.
FGF21 is secreted by the liver during fasting, and helps the body adapt to starvation by increasing insulin sensitivity and blocking the growth hormone/insulin-like growth factor-1 signaling pathway. When there's too much of this growth hormone, it can contribute to insulin resistance, cancer and other diseases.
"Aging and aging-related diseases represent an increasing burden on modern society. Drugs that slow the aging process would be very desirable," says David Mangelsdorf of UT Southwestern. "These findings raise the possibility of a hormone therapy to extend life span."
The hormone does have some downsides: FGF21 overproducers tended to be smaller than wild-type mice and the female mice were infertile. They also had significantly lower bone density than wild-type mice, although they showed no ill effects from this and remained active into old age without any broken bones.
"FGF21 is not affecting their mobility. These guys are spry. They live nice, long lives," says Kliewer. "But the decreased bone density and female infertility will require additional research to determine if it is possible to separate out the hormone's life span-extending effects from its effect on bone."