The changing picture of disease: living longer may not mean living healthier

Big social and demographic changes are driving profound shifts in global health, including sharp rises in the prevalence of conditions associated with old age, urbanisation, and unhealthy lifestyles.

Growing population density, for example, has increased some risk factors for the spread of infectious disease and obesity, while caseloads of cancer and other illnesses of ageing are forecast to rise steeply in lower income countries.

These trends highlight a flip side of the success story that improved longevity, globally. While people are more resilient to some deadly threats, their health during those extended lifespans may be deteriorating in important respects — particularly, if they are poor.

And the dangers are likely to be stoked by demographic shifts, notably a forecast dive in global fertility rates during the rest of the century. That will leave population growth concentrated in a minority of low-income states where people are acutely vulnerable, say experts such as Stein Emil Vollset, a professor at the Institute for Health Metrics and Evaluation and senior author of a wide-ranging fertility study published in March.

“Many of the most resource-limited countries in sub-Saharan Africa will be grappling with how to support the youngest, fastest-growing population on the planet, in some of the most politically and economically unstable, heat-stressed, and health system-strained places on earth,” Vollset says.

Life expectancy increased globally from 66.8 years in 2000 to 73.4 in 2019, according to the World Health Organization. But healthy life expectancy rose only from 58.3 years to 63.7 over the same period — meaning the average number of years not in good health actually increased slightly.

The nuanced picture that longer life does not necessarily mean healthier life is highlighted by WHO data on years of health lost due to death or a medical condition. This damage is measured by a concept known as ‘disability-adjusted life years’ (Dalys), where one Daly represents the loss of the equivalent of a year lived in full health.

Dalys because of communicable diseases such as HIV/Aids and diarrhoeal conditions fell 50 per cent between 2000 and 2019, according to the global health body. By contrast, however, Dalys due to diabetes rose more than 80 per cent, and those linked to Alzheimer’s disease more than doubled over the same period.

One lesson from these figures is how a great modern health boon has resulted in falls in infant mortality, and in certain communicable diseases having less of an impact thanks to better drugs and prevention measures.

But a concern, now, is that this progress could be slowed or even reversed, in part because of the impact of social and environmental changes.

The Covid-19 pandemic showed the potentially devastating effect of greater population densities in urban areas on the spread of communicable diseases. Airborne pathogens can infect people more easily, while overburdened drainage and sanitation systems increase the dangers of contracting waterborne pathogens.

Those same trends in lifestyles and living environments have stoked the spread of non-communicable conditions, too. For example, obesity rates in adults have more than doubled worldwide in the past 30 years and have risen almost twice as fast among children and adolescents, according to a study published in The Lancet in February.

More than 40 per cent of both women and men in the US were obese in 2022, while rates rose sharply in many Middle East, north African, and island nations.

Reasons for this include the increased availability of calorie-heavy processed foods, the often higher cost of healthier alternatives, and many people’s lack of time, space, and facilities to exercise, observers say.

Tedros Adhanom Ghebreyesus, WHO director-general, has warned that getting back on track to meet global targets for curbing obesity will take the “work of governments and communities, supported by evidence-based policies from the WHO and national public health agencies”.

Another far-reaching trend is the way diseases of age once mainly associated with rich-world countries are expected to climb in lower and middle income nations — thanks, largely, to people living longer.

Low- and middle-income countries are forecast to see a sharp rise in prostate cancer deaths, for example. Annual fatalities from the disease will reach almost 700,000 by 2040, a rise of 85 per cent from 2020, according to a Lancet Commission study published in April.

A further health consequence of increased longevity is the growing impact of neurological conditions, such as stroke, dementia and migraine. More than 40 per cent of the global population, or 3.4bn people, suffered nervous system problems in 2021, according to research published in The Lancet Neurology in March.

That drove an 18 per cent rise in Dalys due to neurological conditions between 1990 and 2021 — though, once population growth and increased longevity were adjusted for, both Dalys and deaths fell over the period.

The latest reminder of the multiple dimensions of the disease burden came on Wednesday this week, with the publication of a paper showing disparities between health outcomes for men and women.

The study in The Lancet Public Health found that men disproportionately suffered conditions that led to premature death, such as cardiovascular, respiratory and liver diseases. Women were more affected by problems of illness and disability that often worsened with age, such as musculoskeletal conditions, mental health conditions and headache disorders.

The contrast underscores how living longer does not necessarily mean living healthier — and why the great task now is to improve people’s chances of doing both.

As Luisa Sorio Flor, a University of Washington assistant professor and lead author on the gender health study, puts it: “This report clearly shows that, over the past 30 years, global progress on health has been uneven.”