Evidence of a link between height and longevity has been found by scientists, suggesting that some short people will live longer than their taller peers.
Normal variation in human height is due to a blend of environmental factors, notably diet, and genetic factors.
Now one such inherited factor that could extend the human lifespan by as much as one third in theory has been uncovered, though it may come at the cost of a few inches in height.
The work also suggests that the use of growth hormone as an anti-ageing medicine may actually be shortening lifespan.
And it confirms the emerging view among scientists that rather than being a passive, haphazard process of wear and tear, some people may be blessed with genes that make them more likely to live to a ripe old age.
Earlier work by a French team showed that mice lacking one copy of the gene IGF-1 live on average 26 per cent longer than normal, with females enjoying a bigger advantage (33 per cent increase in lifespan) than males (16 per cent increase).
Damping down the same pathway of the metabolism also resulted in extension of lifespan in yeasts, worms, and flies too. And the same pathway is affected by diets low in calories, the only proven way to extend lifespan.
Now a study by Prof Nir Barzilai, Director, Institute for Aging Research, Albert Einstein College of Medicine, New York, reveals that the same gene is involved in the "oldest old" of people, revealing in the long run how to postpone the physiological ageing process.
Insulin-like growth factor (IGF-1) levels have previously been linked with both ageing and body size, with evidence showing that decreased levels of IGF-1 predispose the animals for short stature, but increased longevity.
To determine if IGF-1 plays a role in human longevity, Prof Barzilai, Dr Yousin Suh and colleagues looked for variations in the gene within a group of Ashkenazi Jewish centenarians and their children.
The researchers used Ashkenazi individuals with no history of familial longevity, matched for age and sex as controls.
Comparing the two groups, the researchers report in the Proceedings of the National Academy of Sciences that centenarians and their offspring were more likely to have a variety of mutations in the IGF-1 receptor which reduced the effects of the factor. As had been shown by the mouse work, the less active IGF-1 pathway had bigger effects on women than men and led to shorter stature.
The work shows that this pathway plays a role in human longevity, which provides new clues as to how to boost lifespan by damping down the action of IGF-1, and other molecules that play a part in this piece of metabolic machinery.
"Practically, this discovery supports the notion that growth hormone, which is injected as anti-ageing medicine in the US (and other countries) maybe dangerous, because it is the people who have low growth hormone levels that are living longer," Prof Barzilai tells The Daily Telegraph. "So avoiding growth hormone may increase ones longevity."
The team does not yet know if longevity is assured by having low growth hormone action throughout life, or whether it is enough to have it decreased at a certain age. "The fact is that growth hormone levels and actions are decreased in old age," he adds.
His team has found other longevity genes - notably CETP and APOC3 - that are also under study to see if there is potential to make anti ageing drugs, though it is too early to speculate on when people will benefit from this understanding.