Stretching lifespans a bit longer has always been the quintessential quest of humankind. Scientists studying ageing have shown in the past that tweaking certain genes can produce the desired results in roundworms, fruit flies and mice. Similar results came through dietary restrictions too.

Now, for the first time, a team of French researchers has shown that by infusing a hormone — commonly used as a drug for sound sleep in humans — can extend the life of a mouse-like mammal, the shrew, by 10 to 20 per cent.

The hormone, melatonin, is better known as the “time-keeping” hormone. Naturally secreted by the body during the night, it tells the body to be ready for the nightfall. It, in other words, keeps the ticking of the biological clock inside an organism synchronised with the day and night rhythm.

Scientists led by Elodie Magnanou, an evolutionary biologist at Laboratoire Arago at the University of Paris, found that when a small nocturnal mammal — the greater white-toothed shrew — was continuously treated with melatonin for three months, it delayed the onset of ageing by three months. The duration is significant as, in captivity, the insect-eating animal has a lifespan of only 30 months. And in the wild, it lives for a much shorter period — 12 to 18 months — perhaps due to exposure to predators and other external conditions.

Magnanou and her colleagues maintained a steady supply of melatonin through an implant placed under the skin of the animals just before they attained the age of 12 months. They found that the first signs of ageing were delayed by at least three months, whereas a second set of animals, which had dummy implants and thus served as control, began showing the symptoms of ageing, as expected, immediately after it completed 12 months. The animals with implants lived three months longer than the others, reported the scientists. The study appeared very recently in the journal PLoS ONE.

The study assumes significance on two counts. First, research has yielded evidence for the first time that a single biomolecule can bring about a substantial delay in ageing. Secondly, melatonin is a commonly used supplement. It has anti-oxidant and anti-depressant properties. Its ability to cure sleep problems has already made it quite popular among people who are continuously on night shift duties, such as those who work at call centres.

The search for the proverbial fountain of youth has been there for thousands of years. The first recorded efforts to combat ageing and extend lifespans date as far as back to 3500 BC.

Though the biological processes involved in ageing still continue to be a mystery by and large, scientists have received some vital clues about certain genes that play an important role in this.

The most well known study on genes involved in longevity was conducted by Cynthia Kenyon of the University of California San Francisco in 1995. She found that by making small changes to a gene called daf-2, roundworms could be made to live twice their lifespan. The gene, she had found, triggers a number of complex changes in the organism’s metabolism.

Once tweaked, daf-2 exerts an influence on several other genes involved in metabolic and anti-microbial functions, controlling cellular stress, and dampening the activity of specific life-shortening genes. Kenyon’s lab found that daf-2 affects the lifespan of organisms also through a second gene, known as daf-16, whose function was known to control the expression of other genes.

Scientists have known for long that calorie restriction has a desirable effect on longevity. They have found that underfeeding an organism, such as the ordinary roundworm, alters its endocrine function, which regulates the production of hormones instrumental in metabolism. But how this happens largely remained a mystery till a significant study at the Massachusetts Institute of Technology (MIT) in 2007 by Leonard Guarente and others. The study which appeared in Nature showed that a gene — found in a particular pair of sensory neurons that communicate with the endocrine system — plays an essential role in lengthening their lives.

The scientists found that when the worm is underfed, and thereby a calorie reduction is induced, the gene skn-1 present in these two neurons gets activated. Once activated, the gene gives instructions through the neurons that inform the cells about food availability. As a result the cells increase their metabolic activity, and this enhanced metabolism makes the worms live longer than their normally fed counterparts.

What sets the present study apart from the earlier ones is its simplicity and possible immediate application. Says Magnanou, “Our next step is to understand melatonin’s influence on ageing. Once we understand its mode of action, we can perhaps envisage its use on humans.” However, she warns against simply extrapolating their results to human beings.