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Over the past century, human life expectancy has risen at a pace that would have astonished earlier generations. In 1900, the average person born anywhere in the world could expect to live to around thirty-two. Today, global life expectancy is over seventy, and in many wealthy countries it is above eighty. Much of this increase came from reducing deaths in childhood, through clean water, vaccines and better nutrition, but people are also living longer in old age.
Yet a longer life is not necessarily a healthier one. Researchers increasingly distinguish between lifespan, the total number of years a person lives, and "healthspan", the number of years lived in good health. According to estimates by the World Health Organization, people around the world spend, on average, roughly the last nine to ten years of their lives in poor health. The concern among many experts is that gains in lifespan may simply add more years of illness and disability at the end of life.
This is not inevitable. As long ago as 1980, the American doctor James Fries proposed what he called the "compression of morbidity". If the onset of chronic illness could be delayed more than death itself, he argued, people would spend a smaller proportion of their lives unwell, and serious illness would be squeezed into a short period at the very end. Whether this has actually happened is a matter of debate; the evidence varies between countries, diseases and social groups.
What is clearer is that many of the main causes of long-term illness, such as heart disease, type 2 diabetes and some cancers, are strongly influenced by behaviour and environment. Regular physical activity, a balanced diet, not smoking and limiting alcohol all reduce risk. Increasingly, researchers also emphasise less obvious factors. Loneliness and social isolation, for instance, have been associated with poorer health outcomes, and some studies suggest the effect may be comparable to that of well-known risks such as smoking, although such comparisons should be treated with caution.
Inequality matters too. In many countries, the gap in healthy life expectancy between the richest and poorest areas is considerably larger than the gap in life expectancy itself. People in poorer neighbourhoods not only tend to die younger but also spend more of their shorter lives in poor health.
The challenge for the coming decades, then, is not simply to add years to life, but to add life to years. That requires not only medical advances but also policies that make healthy choices easier for everyone, from safe places to walk and exercise to affordable healthy food and communities in which older people remain connected and valued.