Some people who live to 100 and beyond smoke, drink hard liquor and down a beer every evening. Others indulge in daily ice cream or even drink three glasses of Dr. Pepper. This paradox is one reason several scientists who study extreme aging were not surprised by a recent study showing that longevity is roughly 50% genetic and 50% environmental — a substantially higher genetic contribution than earlier research indicated.

The take-home message isn’t that your time on Earth is pre-ordained by your genes. A closer look beyond the headlines reveals something both more promising and more intriguing. For most of us, a healthy diet, regular exercise and adequate sleep can dramatically improve the chances of living a longer, healthier life.

Yet a small minority of people are born with a rare combination of genes that actually slows the aging process. These genes make them less susceptible to the usual age-related killers — heart disease, Alzheimer’s and cancer — even when they don’t consistently follow their doctors’ advice.

You don’t have to change people’s genes to extend longevity. Researchers are beginning to unravel how these genes work and are trying to replicate their effects in the rest of us through drugs or other interventions. At the same time, they’re also working toward tailoring medication and dietary advice to an individual’s genetic makeup.

The new study, published in Science and led by researchers at the Weizmann Institute of Science in Israel, drew widespread attention for showing that genes play a larger role in longevity than previously believed — contradicting the major 2018 headlines that suggested that genes mattered much less. That earlier research relied on genealogical records stretching back several centuries and may have estimated a much lower genetic contribution — about 7% — because so many people died from infectious diseases.

Several other studies have placed the genetic contribution to longevity at about 20%. But scientists who study aging say these findingsaren’t always measuring the same thing. The latest research combined multiple datasets and employed a mathematical model to filter out deaths from accidents, infectious diseases and other causes unlikely to be influenced by genes.

Those factors played an even greater role in earlier centuries when widespread early death kept average life expectancy well below 50. Today, life expectancy in the U.S. has increased to nearly 80, even though the human genome hasn’t changed.

A key concept is that the balance between genetic and environmental influences changes as people age. "It’s really important to make a distinction between what it takes to get into your early 80s, versus what it takes to get to around 100, versus even older ages like 105 or even 110,” said Thomas Perls, a geriatrician with Boston University Medical Center.

Perls, founder and director of the New England Centenarian Study, estimates that longevity into the mid-80s is about 25% determined by genes and 75% determined by environmental exposures and health behaviors. Using data collected by his research group, he found that reaching age 100 was 62% heritable, while surviving to even older ages was closer to 80%.

Healthy behaviors, he said, include eating a nutritious diet, maintaining a healthy weight, exercising regularly, not smoking and drinking alcohol only very occasionally, if not at all. Also important, he added, are managing stress effectively and having a positive attitude toward aging.

Other researchers agree that a larger genetic role at extreme ages doesn’t diminish the benefits of exercise, sleep and diet. We should try to optimize all of those, said Nir Barzilai, director of the Institute for Aging Research at the Albert Einstein College of Medicine. But for a fortunate few, even unhealthy habits fail to shorten their lives.

In a 2011 study of 477 people between the ages of 96 and 109, Barzilai and his colleagues at Yeshiva University’s Institute for Aging Research found that these individuals actually had slightly worse behaviors than control subjects. About 50% smoked, roughly half were obese or overweight and fewer than 50% engaged in even moderate exercise. "So as a group, they didn’t behave right at all,” Barzilai said.

Despite this, they carried just as many genes associated with cancer, Alzheimer’s disease, heart disease and diabetes as the control group. Their advantage was instead linked to carrying genes associated with a slower aging process — genes that appeared to protect them from those diseases, just as youth protects younger people.

How do these so-called anti-aging genes work? Barzilai said they tend to suppress hormones that promote growth. Several existing drugs may also do this, including the diabetes drug metformin and widely used GLP-1 inhibitors for diabetes and obesity.

Another reason to suspect that genetic influence increases with age is provided by historical trends. Although life expectancy has risen dramatically in the last century, the proportion of people who live to 100 has changed very little, said Paola Sebastiani, a biostatistician at Boston University.

Researchers also caution that we shouldn’t assume all environmental factors are within individual control. Longevity is closely linked to socioeconomic status and exposure to air pollution, among other factors. Helping everyone live a longer, healthier life requires society to make healthy living more accessible and affordable.

Many of the rare elite agers who top 100 do so without becoming frail, spending fortunes or eating extreme diets of blended vegetables and supplements. Jeanne Calment, the French woman often cited as the longest-lived person on record, reportedly took up smoking when she was living in a nursing home at age 112 — and then lived another decade. Still, for most of her life, she exercised regularly, ate fresh foods and took good care of herself. That combination gives scientists a reason to hope that more of us could one day approach 120 while remaining healthy and enjoying life.

© The Japan Times