Brain insulin reduction 'improves longevity'

News sources reported that keeping a healthy weight may help people to live longer by limiting brain exposure to insulin. The stories were based on research in mice which found that those with reduced brain insulin lived longer.

The study was not directly set up to look at the link between weight or diet on lifespan. In light of this and the fact that the study is in mice, this interpretation for human health may be premature.

Where did the story come from?

Researchers from Harvard Medical School in Boston, Massachusetts conducted the research behind these news stories. The study was published in the peer-reviewed medical journal, Science .

What kind of scientific study was this?

This was an animal study involving mice with a particular mutation which meant they had reduced insulin either in their brains only or in all their tissues. These mice were maintained on a high-energy (high calorie) diet.

The researchers assessed the effects of a mutation in mice (which meant they used less insulin in the brain) on their life span, glucose tolerance, fat and carbohydrate oxidation, and on chemicals in the brain that protect against oxidative stress. They compared these characteristics against normal mice (mice without the mutation that affected their insulin use).

What were the results of the study?

The researchers found that mice that used less insulin in the brain lived on average 17% longer than normal mice.

What interpretations did the researchers draw from these results?

Among the researchers’ conclusions is the finding that reducing insulin in the brain increases the lifespan of mice maintained on a high-energy diet by about five months. They report that "by directly decreasing the use of insulin in the brain, an ageing brain can be shielded from the negative effects of high levels of insulin that ordinarily develop with overweight and advancing age".

What does the NHS Knowledge Service make of this study?

The research appears to have been well conducted and certainly generates some interesting findings.

• It is not clear from the researchers’ methods how many mice were involved in this experiment which is an important point because smaller studies are by nature less reliable than larger ones.
• Importantly though, as the study was conducted in mice, we cannot immediately see the benefits of the findings for humans. We must await the results of further research into the mechanisms by which insulin protects against ageing before the implications for treatments in humans can be fully understood. This is particularly important in light of the fact that the mice in this study were maintained on a high calorie diet, had mild glucose intolerance, and were heavier than the controls; all of which have known implications for the health of humans.