Your potential life span is written in your genes, according to a new study. You can lengthen it a bit with a healthy lifestyle. But if your genetic potential is to live to be 80, for example, it is unlikely that anything you do will push your age at death up to 100.
That, at least, is the conclusion of a paper published Thursday in Science.
Uri Alon of the Weizmann Institute of Science in Israel and other researchers drew the data for the study from three sets of data from pairs of Swedish twins, including one set of twins that was reared apart. To test how generalizable the results are, the group also examined data from a study of 2,092 siblings of 444 Americans who lived to be over 100. Their goal was to identify outside factors that can affect how long someone lives, like infections or accidents, separate from the intrinsic factor of genetics.
They report that aging is mostly hereditary, a conclusion that flies in the face of much conventional medical wisdom regarding dieting, exercising and healthy habits. These habits are important for the quality of a person’s life, but they run into another form of conventional wisdom: You can’t make someone into a centenarian, unless that person also has a genetic inheritance of longevity.
“If you are trying to gauge your own chances of getting to 100, I would say look at the longevity in your family,” said Dr. Thomas Perls, a geriatrician and the director of the New England Centenarian Study at Boston University. His study’s published data on U.S. centenarians were used in the new analysis, although he was not associated with the study.
“This paper has a pretty powerful message,” said S. Jay Olshansky, an emeritus professor of epidemiology at the University of Illinois, Chicago, who was not involved in the study. “You don’t have as much control as you think.”
“Some of us are driving a Mercedes and some are driving a Yugo,” he said, referring to the low cost, compact car from the former Yugoslavia.
The study’s conclusions — that genes are powerful drivers of how long people can live — is consistent with what is known about other species, said Daniela Bakula of the University of Copenhagen. Dr. Bakula, a co-author of an outside perspective published by Science alongside Dr. Alon’s paper, added that life spans of every other organism studied, “have a strong genetic component.”
The new paper used statistical and mathematical models to eliminate causes of death that did not seem to be associated with aging in the cohorts they studied.
That sort of analysis, Dr. Olshansky said, is difficult, and “exceptionally well done,” in the paper, he said.
The researchers used mortality data on Swedish twins born between 1900 and 1935, a period that, despite world wars, the Great Depression and a flu pandemic, saw improvements in sanitation and medical care. It was, Dr. Alon said, “a natural experiment” — a number of extrinsic factors affecting mortality had gone down.
That let his group to study the effects of those factors. To test their results, they compared them with life span from another study, of Danish twins born between 1870 to 1900. In those years, there were many deaths at early ages from infectious diseases like diphtheria and cholera.
The Swedish studies included a few causes of death; cancer, cardiovascular disease and dementia. Dr. Alon and his colleagues found that cancer was least likely to be affected by genetics while dementia was the most likely.
Ultimately their analyses led to an estimate that genes account for more than 50 percent of the differences in life spans in a population, compared with the 25 percent or less that had been suggested in earlier research.
The reason for the disparity compared with previous studies, Dr. Alon said, is that those studies included people who had died at younger ages, from causes like accidents or illnesses that were not related to their genes. Then, if genes played a minor role, it was assumed that lifestyle played a major one.
Dr. Alon does not dispute that lifestyle is important. He calculated that certain healthy or unhealthy habits can add or subtract 5 years or so from a life expectancy determined by the “luck of the draw” represented by genes. A person with a genetic predisposition to live to be 80 might die at 75 if they had no healthy habits. If they had every healthy habit they might live to be 85.
Or, as Dr. Olshansky put it, reaching a very old age “is not possible unless you’ve already won the genetic lottery for longevity at birth.”
Dr. Bradley J. Willcox, director of geriatric research at the University of Hawaii, who directs the studies of aging at Kuakini Medical Center in Honolulu, called the paper “provocative.” But he said he was not entirely convinced.
“Drawing a clear, bright line between intrinsic and extrinsic causes of death is not possible,” he said. “Many deaths live in a gray zone where biology and environment collide.”
For example, he said, genes can shape how lethal an infection becomes. “If you change how you label those borderline cases,” he added, “you change the results.”
The strong effect of genes on life span does not mean that lifestyle can be ignored, Dr. Perls said, especially for those who do not have the genes of centenarians. Sticking to a good diet, not smoking, maintaining a normal weight and getting regular exercise can all make a notable difference in how long a person lives. He added that good habits could be of even more help than Dr. Alon suggested when he had said the difference between age of death with nothing but good habits compared with no good habits can be 10 years.
Dr. Perls noted that observational studies from Harvard found that a woman who is 50 years old, with healthy habits, could live to be 93. If she had none of those habits — if she smoked, had an unhealthy diet, did not exercise, and drank more than very modestly — she would live to be 79. For a 50-year-old man, a healthy lifestyle could allow him to live to age 88 instead of 76.
But, Dr. Perls said, when it comes to living to a very old age — well over 90, or even 100, or more — genes are important contributors.
Yet even for people who have won the genetic lottery, Dr. Olshansky said, “it’s easy to shorten your life but very difficult to lengthen it.”
Gina Kolata reports on diseases and treatments, how treatments are discovered and tested, and how they affect people.
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