[pronut-hiv] BBC: Healthy weight link to longevity

["ProNut-HIV" <pronut-hiv@healthnet.org>]

Keeping a healthy weight may help people live longer by limiting brain
exposure to insulin, say US scientists. 
A study in mice found that reducing insulin signals inside brain cells
increased lifespan. 

Writing in Science, the researchers said a healthy lifestyle and weight
reduce insulin levels in humans and may have the same effect. 

Experts said, if proven, insulin would be just one of many factors, such
as genes, that influence longevity. 

Previous research in fruit flies and roundworms has suggested that
reducing the activity of the hormone insulin, which regulates blood
sugar levels, can increase lifespan. 

The latest study looked at the effects of a protein, IRS2, which carries
the insulin signal in the brain. 

Mice who had half the amount of the protein lived 18% longer than normal
mice. 

Despite being overweight and having high levels of insulin, the mice
were more active as they aged, and their glucose metabolism resembled
that of younger mice. 

The researchers said the engineered mice were living longer because the
diseases that kill them, such as cancer and cardiovascular disease, were
being postponed due to reduced insulin signalling in the brain, even
though circulating levels of insulin were high. 

They said, in the future, it may be possible to design drugs to reduce
IRS2 activity to reproduce the same effect, although they would have to
be specific to the brain. 

Weighty problem 

Study leader Dr Morris White, an investigator at the Howard Hughes
Medical Institute, said the simplest way to encourage longevity was to
limit insulin levels by exercising and eating a healthy diet. 

He said: "Our findings put a mechanism behind what your mother told when
you were growing up - eat a good diet and exercise, and it will keep you
healthy. 

"Diet, exercise and lower weight keep your peripheral tissues sensitive
to insulin. 

"That reduces the amount and duration of insulin secretion needed to
keep your glucose under control when you eat. 

"Therefore, the brain is exposed to less insulin."

His team is now planning to look at possible links between IRS2
signalling and dementia, which research has shown is associated with
obesity and high insulin levels. 

Matt Hunt, science information manager at Diabetes UK, said: "This is an
interesting study as the work done on mice could suggest that insulin is
playing a role in the ageing process. 

"Nevertheless, we are looking at numerous and extremely complex gene
interactions in the brain and this research doesn't yet explain how this
mechanism might be working." 

He said that human longevity had been steadily increasing, despite
rising levels of obesity and diabetes suggesting that insulin levels in
the brain would be only one of many factors involved. 

"We welcome the fact that this study supports our key message of the
importance of leading a healthy lifestyle."