Women tend to live longer than men, but a global review of mortality data from 1990 to 2010 suggests the gender gap in life expectancy is narrowing.

The study is based on a statistical analysis of United Nations data, which grouped 194 countries into 'clusters' of similarity based on measurable factors that influence mortality.

Compared to 1990's statistics, every cluster of nations showed consistent or improved life expectancy by 2010. There was also a substantial shrinking of the male-female gap in mortality.

On a global average, women today tend to live about four or five years longer than men, although in some nations, like Russia, women can live nearly ten years longer than their male counterparts.

Why that gap exists is relatively unclear, and while some of it is probably biological, there are other influential factors that determine an individual's mortality, many of which depend on changes in society and the environment.

For instance, while some nations, like South Africa, saw massive declines in life expectancy from 1990 to 2010, these exceptions were largely due to local factors like the HIV/ AIDS epidemic, ebola, malaria, war, or famine.

If the overall global trend stays roughly the same going forward, the gap between the sexes could diminish even more by 2030, predict researchers at the University of Alcalá and the University of Barcelona in Spain, along with an expert from the University of Oxford.

This is true of both higher and lower income nations, although the higher income nations tend to show diminishing returns in life expectancy over time.

Still, in regions like Australasia, Europe, and North America, researchers estimate a notable decline in mortality rates among older aged individuals by 2030, though degenerative diseases will continue to be a leading cause of death.

Japan, Australia, and some western European countries are likely to top the charts for longevity indicators in the years to come.

In 2010, the US was among that top rank, but researchers predict it will fall into the second- or even third-place cluster by 2030.

Deaths associated with drug use are increasing to frightening levels in the US, and it is undermining the nation's future health progress.

Some estimates suggest that by 2029, the US could experience a million more opioid deaths.

The current predictions are only based on ten years of data, so their inferences need to be taken with a grain of salt. For instance, the last few years have seen previous increases in life expectancies stall across many countries due to COVID-19, with a greater impact on men's life expectancies than women's, but this may only be a temporary departure from the overarching trending increase.

That said, physician scientist Brandon Yan, who was not involved in the study, told Chen Ly at New Scientist that the results are "consistent with epidemiologic trends that would suggest a rise in global life expectancy and a narrowing of the gender gap over time."

Lead researcher David Atance and colleagues have run the numbers and predict that most nations will see their longevity trends continue into the future.

By 2030, they found Latin American countries are likely to obtain the best mortality indicators after high-income regions, with particularly significant gains made in improving male life expectancy.

In countries that have confronted disease, famine, violent conflicts, and war in recent years, like those in Africa and the Middle East, male life expectancy is also expected to improve.

By contrast, life expectancy gains in Eritrea, Ethiopia, Madagascar, Rwanda, Sudan, Tanzania, and Zambia, will be mainly produced in the female population, as socioeconomic and political conditions improve.

The worst outcomes are predicted in the Central African Republic, Côte de I'voire, Lesotho, and Zimbabwe. These nations were all involved in wars and experienced social, economic, and political turmoil over the past decade.

None of this, of course, takes into account new economic, social, or political developments that might arise in the coming years.

Time will tell whether future improvements in life expectancy actually occur, especially as climate change threatens millions of lives in both high- and low-income nations.

The study was published in PLOS ONE.