Worms "stop ageing" when they are starved of food and can go onto live twice as long as normal, a new study has shown.

一项新研究发现，蠕虫在缺乏食物的情况下会“停止老化”并能存活正常情况下两倍的时间。

Researchers found that nematode（线虫） worms entered a state of arrested development（发育停滞） when food was taken away from them.

They continued to move and forage but their cells and organs were suspended in an ageless, inactive state.

Once the worms had access to food again, they began to grow normally and doubled their lifespan.

Scientists from Duke University, North Carolina, US reported their findings in the journal PLOS Genetics.

Organisms including flies, yeast, monkeys and worms have previously been put on diets and shown to have their life spans extended by 30 to 200%, compared with those able to eat normally.

But how it happens remains unclear.

The research team set out to determine how growing tissues respond to starvation.

Tiny nematode worms - Caenorhabditis elegans (C.elegans) - which are normally found underground, were chosen because they reach adulthood in three to four days and develop in similar ways to each other.

They are also translucent and composed of only a few hundred cells, making changes in development easy to see under a microscope.

In the wild, the worms can experience bouts（来回一次） of feast or famine（饥荒） that are likely to affect their development and lifespan.

The authors allowed the worms to grow to a specific developmental stage, just before the start of rapid cell growth.

Food was then removed from the worms and their reactions observed.

Within hours the worms' development stopped. Once the worms could feed again, their development resumed and they grew into normal adults.

The authors found that worms' development was not continuous but stopped at two main stages, which they called checkpoints.

They explained that a worm needs enough nutrients to pass through to the next developmental stages. If it is deprived of nutrients it has to wait until it has built them back up before its development can continue.

"Organisms have to monitor their environment and decide whether or not it is amenable（有责任的） to their development," lead author, Adam Schindler said. 

"If it isn't, they stop. If it is, they go. Those checkpoints seem to exist to allow the animal to make that decision. And the decision has implications, because the resources either go to development or to survival."

The study found the worms could be starved for at least two weeks and still develop normally once they were fed. 

The period of arrested development allowed the worm to double its normal two-week lifespan.

Mr Schindler said: "From an evolutionary perspective this finding highlights the importance of an effective response to starvation for optimal fitness (survival and the passing on of genes to the next generation) of the organism."

The team say their work may have implications for human ageing and also cancer biology, especially as the behaviour discovered in worms is similar to tumours lying dormant（休眠的） for years before growing again.

They are now performing genetic studies to see if they can find another way to force worms to pause their development.

"The main question is how the decision is made to either arrest development or continue," Mr Schindler said. 

"Understanding the key players in this decision could provide insights into why tissues degenerate during ageing and reveal possible ways of slowing this degeneration."