The U.S. has the biggest lifespan-health span gap in the world. New study shows we’re living longer lives — but not in good health.

People are living longer than ever before — but they’re not actually healthier. And the number of years spent sick is only growing, according to a massive new study just published in JAMA Network Open. While researchers found that this is a global phenomenon, the so-called health span-lifespan gap is wider in the U.S. than anywhere else in the world. In America, the gap between how long people live and how long they live in good health is over 12 years.

Experts say it begs the question: We’ve gained more years, but at what cost? Here’s what the landmark research tells us, and how we might close the gap between years lived and years lived well.

What is the difference between health span and lifespan?

Lifespan is simply a measure of how long someone lives or, collectively, how long we live on average at the population level. It’s cold hard math, and doesn’t tell us much about what living is like. In recent years, experts have looked to the notion of health span to measure quality of life. Health span refers to how long someone lives in, well, good health.

“There are these big debates, as we increase lifespan: Those extra years gained … are they going to be healthy years or miserable years?” Michael Gurven, a professor of anthropology at the University of California, Santa Barbara Center for Aging and Longevity Studies, who was not involved in the study, tells Yahoo Life. “Of course, no one wants the latter, and this is why health span has been the big buzzword recently.”

For the new study, researchers gathered data on the average lifespans of people in the 183 member-nations of the World Health Organization (WHO). Then, to assess the average health span of each country, they assigned a score to each disease or ailment that might cause disability or a generally poorer quality of life. These included chronic conditions like heart disease and arthritis, as well as health problems such as mental health disorders and dependency on drugs or alcohol. Researchers then created an estimate of how many years of healthy life a country’s population lost due to the burden of each of these factors. The answer? In most countries, many years. The difference between the average lifespan, minus the number of unhealthy years, estimated what the researchers call the health span-lifespan gap.

The global lifespan is nearly a decade longer than the average health span

The study found that an average global citizen lives 9.6 fewer healthy years than they live altogether — so, for example, someone who lived to 80 might have spent the last decade of their life in poor health. That disparity is even more stark for women, for whom that gap is 2.4 years wider compared to men.

Researchers say the global gap is also widening. Over the past 20 years — between 2000 and 2019; the study doesn’t include data from 2020 through the present — the average lifespan worldwide has extended by 6.5 years. But the number of healthy years one can expect to live has only increased by 5.4 years. Our health span is not keeping pace with our longevity. Keep in mind that these estimates are for an entire population, so this doesn’t necessarily mean that everyone, everywhere, can expect the last 10 years of their lives to be spent debilitatingly ill. Some people live relatively long, healthy lives, even with chronic disease, the study authors noted. And others may experience their most unhealthy period of life somewhere in the middle due to addiction or cancer.

According to the findings, the majority of the health span deficit can be attributed to non-infectious diseases, which include heart disease and diabetes — and which have cumulative effects that typically come to a head in old age. “Aging itself is a very important factor in the development of chronic diseases, so that’s an unintended consequence of people living longer,” Armin Garmany, an MD-PhD candidate at the Mayo Clinic and study co-author, tells Yahoo Life.

His co-author, Dr. Andre Terzic, who pioneered regenerative medicine at the Mayo Clinic, says they are now looking into why this gap exists and is widening. “But suffice to say that clearly there is an association [with] … chronic diseases that the world, in general, is more and more afflicted with, such as cardiovascular disease, but also cancer, diabetes and neurological disease, etc.,” he adds.

The U.S. has the widest health span-lifespan gap

The average life expectancy in the U.S. is 77.5 years, according to the Centers for Disease Control and Prevention. But Americans outlive their health spans by 12.4 years, the study found. It’s closely followed by Australia (which has a gap of 12.1 years), New Zealand (11.8 years), the U.K. (11.3 years) and Norway (11.2 years). Several countries in Africa fall at the bottom of the health span-lifespan gap rankings, but this is less due to longer health spans than to the fact that lifespans are relatively short, as there have been fewer advancements to prevent deaths from infections or to allow people to live with chronic diseases.

Just as in other countries, chronic conditions like heart disease are major factors in how many years Americans remain alive but in poor health. But, the authors add, a high burden of mental health and behavioral conditions — which the WHO groups together, and include depression, anxiety and addictions to alcohol and drugs — are also weighing heavily on our health span, as well as curtailing life expectancy in the U.S.

Underpinning both chronic diseases and what are sometimes called deaths or diseases of “despair,” such as addiction, is the prevalence of loneliness, stress and inequality in the U.S., Gurven says. “It’s hard to avoid that living in a highly unequal society is stressful and that takes a toll on our health in so many ways,” he says. That inequality affects not only access to health care, but can also be seen in how little opportunity there is for Americans in many parts of the country to get physical activity or healthy meals in their busy days, helping to fuel the obesity epidemic, which, in turn, curtails health span.

Why it matters — and what to do

The main takeaway, Gurven says, is that “yes, lifespan has been increasing over the past two decades, but a lot of those years are not being spent in a healthy state.” Not only does that inflate health care costs to individuals and their countries, it’s simply not what most people want. Older people and aging experts often value quality of life over quantity.

If more people lived healthy lifestyles — eating a balanced, heart-healthy diet, exercising, maintaining a healthy weight and so on — that gap would likely narrow, but we can’t rely on individual “willpower” alone, says Gurven. He, Terzic and Garmany all agree that both behavioral changes and more effective health care practices will be crucial to closing the health span-lifespan gap. Terzic hopes that technologies like AI will soon help usher in an era of “interceptive medicine,” allowing doctors to identify people at risk of shorter health spans, and intervene before a chronic disease takes hold.

But some changes that could make a difference are far more low-tech. These include easier access to fruits and vegetables and more sidewalks and protected bike lanes, says Gurven. “A lot of this relies on the structured environment,” he says. “When everything relies on our [individual choices], everything works against us.”