Interesting insights emerge on human lifespan

Life expectancy in India at the time of independence was approximately 30-32 years. This rather low figure was driven by widespread poverty, inadequate healthcare, malnutrition, and high infant/maternal mortality rates. Since 1947, life expectancy has more than doubled, rising to over 70 years in recent years. This is, by itself, considered to be a major milestone as it reflects an improved public health care in the country. With about 65 per cent of Indians currently under the age of 35 and the median age speculated to be around 29, lifespan is a constant subject of interest.

With a senior citizen population of around 11 per cent of the total, many a time the statement ‘age is just a number’ is bandied about in social circles. It thus becomes interesting to know how a human being’s lifespan can be computed; some recent studies are helpful in this regard. Genetics may explain about half of a person’s lifespan, a study has suggested, pointing to a far more significant role of genetics than indications from earlier research. The findings, published in the journal Science, show that once mortality due to external factors such as accidents or infections are accounted for, “heritability of human life span due to intrinsic mortality is above 50 per cent”.

Researchers from Israel’s Weizmann Institute of Science and Karolinska Institutet in Sweden pointed out that understanding the heritability of human life span is central to ageing research, yet measuring genes’ influence on longevity remains a challenge. Earlier studies have estimated that life span may be 15-33 per cent heritable across varied populations, with a typical range of 20-25 per cent, they said. The researchers show that the estimates “are confounded by extrinsic mortality -- deaths caused by extrinsic factors such as accidents or infections”.

While genes linked to lifespan have been identified, external environments like disease or living conditions can exert a powerful influence on how long one lives and often obscure or confound potential genetic effects, they said. “Extrinsic mortality systematically masked the genetic contribution to life span in traditional analyses,” the authors wrote. The team added that historical data from twin studies -- often explored for understanding how genes interact with environment and contribute to noticeable traits -- lack sufficient cause of death information to correct for extrinsic mortality.

“We use mathematical modelling and analyses of twin cohorts raised together and apart to correct for this factor, revealing that heritability of human life span due to intrinsic mortality is above 50 per cent,” they said. “Correcting for extrinsic mortality raises the estimate for the heritability of human life span in twin and sibling studies to (nearly) 55 per cent, more than twice previous estimates and in line with heritability of most human traits,” the team added.

All the same, for humans around the world, it would be far more important to add life to years than add years to life as another popular saying goes. With quality of life under constant strain owing to prevailing socio-economic conditions, lifespan, whether inherited or lived