The Mail Online reports that "Britain and the US are the only 2 western nations where life expectancy is falling," describing a study looking at changes in longevity in high-income countries.

Researchers in the US looked at changes in life expectancy across 17 high-income countries over recent years.

They particularly focused on annual changes between 2014 and 2016, as previous work had suggested that life expectancy in the US stopped improving during that time.

The researchers found a number of countries, including the US and the UK, experienced decreased life expectancy from 2014 to 2015.

In the UK, life expectancy at birth declined by 0.19 years for women and 0.26 years for men.

But while most other countries bounced back from 2015 to 2016, the US and the UK did not.

This study gives some interesting insights into differences in life expectancy between economically similar countries. But it can't explain the reason why.

To understand these differences further, we'd need to see not only whether there have been changes in cause of death, but also changes in other things that affect people's health and wellbeing across their lifespan.

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Where did the story come from?

The study was carried out by researchers from the University of Southern California and Princeton University in the US.

The researchers were funded by grants from the Robert Wood Johnson Foundation and the US National Institutes of Health.

It was published in the peer-reviewed British Medical Journal.

Mail Online's reporting highlighted the issue of deaths related to the flu outbreak of 2014 to 2015.

Although the study did look at the effect this had on the drop in life expectancy, it only found this to be a contributing factor in a small number of countries.

Both The Guardian and the Mail Online correctly highlighted that while many countries experienced a drop in life expectancy during the 2014 to 2015 period, only the US and the UK failed to recover from that.

The Guardian also highlighted the suggestion that one probable reason for the drop in US life expectancy is the ongoing opioid epidemic (both legal and illegal) in the country.

What kind of research was this?

This was a retrospective cross-sectional study comparing trends in national mortality data across multiple countries over several years.

This allowed researchers to look at geographical patterns in mortality on a very large scale that would have been hard to achieve if they'd set up a new study from scratch.

The disadvantage of this approach is it can only tell us general patterns in mortality across different populations, but can't fully answer why.

The study didn't allow the researchers to follow people over a longer period of time so they could understand all the various factors that may have contributed to their deaths.

What did the research involve?

The researchers wanted to look at recent trends in life expectancy in the US and compare these with 17 other high-income countries to see if there were any differences.

The countries compared included Australia, Canada, France, Germany, Italy, Japan, Spain, Switzerland and the UK.

They took data from the Human Mortality Database, a resource created by researchers from the US and Germany. It contains detailed information about mortality and populations from a number of countries.

For countries or years not covered by that database, data from each country's own mortality statistics databases was used.

The researchers constructed life tables to calculate the life expectancy of people in different age groups. They created separate life tables for 1990, 1995, 2000, 2005, and every year from 2010 to 2016.

They were particularly interested in looking at data from 2014 to 2016, as previous work showed that the US had a decline in life expectancy during that period and they wanted to see whether the same was true in other countries.

The researchers looked at 22 different categories of cause of death, which didn't overlap, to see whether there may have been changes in individual causes.

They also wanted to test the idea that the drop in life expectancy during that period in the US may have been related either to flu outbreaks or drug-related causes, such as overdoses.

What were the basic results?

The researchers reported findings for all 17 countries.

For the UK, the life expectancy of babies born during 2014 to 2015 dropped by 0.26 years for males (95% confidence interval [CI] -0.20 to -0.32) and by 0.19 for females (95% CI -0.13 to -0.26).

The biggest improvement in life expectancy at birth was in Finland: a gain of 0.34 years for females (0.15 to 0.53) and 0.50 for males (0.28 to 0.71).

The biggest decline was in Italy: a decrease of 0.55 years for females (-0.60 to -0.49) and 0.43 for males (-0.50 to -0.37).

For women aged 65 and under in the UK, there was a slight increase in life expectancy of 0.013 years, but men in the same group had a drop in life expectancy of 0.031 years.

Both men and women over 65 in the UK had a decline in life expectancy in this period (a drop of 0.297 for women, 0.154 for men).

The researchers found many countries experienced drops in life expectancy during the 2014 to 2015 period, but then recovered. The US and UK, however, didn't seem to improve after this period.

Increased deaths caused by flu outbreaks or pneumonia were only found in 3 countries: Italy, Germany and the US.

How did the researchers interpret the results?

For the UK results, the researchers highlighted that most of the decline in life expectancy had been for older adults (aged 65+).

Across all non-US countries the main causes of death that seemed to be behind the decline in life expectancy were respiratory diseases, circulatory diseases, Alzheimer's disease, nervous system diseases, and mental disorders.

In the US, overdoses (specifically opiate overdoses) were among causes of death suggested to be behind the decline.

The researchers noted that previous research suggested that some of the decline may be due to decreases in funding to health and social care, but said further work was needed to test this idea.

Conclusion

This research highlights some important changes to life expectancy across several countries. The main limitation is that it can't answer the reason for the decline in life expectancy.

The study tried to look at whether changes in cause of death may have contributed to the decline in life expectancy in some countries.

But it can't explore the probably complicated chain of events behind each of those causes of death to find explanations for the changes.

Various environmental, sociodemographic, health and lifestyle factors could all be having an influence.

As such, this research can't provide answers for the ways in which countries could potentially improve their health and social care systems to reverse the changes.

This finding could also be a temporary unexplained variation that will reverse again in a year or so.

Still, the study provides an interesting comparison, showing that levels of life expectancy can vary between high-income countries.

If you'd like advice on how to maintain good health as you get older, see our advice on healthy ageing (PDF, 1Mb).

Analysis by Bazian

Edited by NHS Website