South Africans are likely to live, on average, seven years longer in 2040 than they do now, but the country will see only modest improvement in its global ranking as longevity increases worldwide, according to a study published in the Lancet on Wednesday .

SA had an average life expectancy of 62.4 years in 2016, and ranked 171 among 195 countries. If recent health trends continue, SA could see life expectancy increasing to 69.3 years. But it will only rise two places in the global rankings, to 169, as life expectancy is expected to increase in most countries.

Spain is expected to rank first in 2040, with an average lifespan of 85.8 years, followed by Japan with life expectancy of 83.7 years.

The authors of the study forecast a range of scenarios for each country, which for SA show that life expectancy could increase by as much as 12.9 years to 75.3 years if the country stepped up its efforts to improve the health of the nation. But in the worst-case scenario, life expectancy could fall by as much as 8.1 years.

“The main message here is that our health is not preordained. With the [right intervention] our health can improve; if not, we are in for a rough ride,” said SA Cochrane Centre director Charles Wiysonge, who was not involved in the study.

The study forecast a large global shift in deaths from infectious diseases to deaths from noncommunicable diseases such as diabetes, chronic obstructive pulmonary disease, kidney disease and lung cancer.

The top 10 causes of death in SA in 2016 were HIV/Aids, lower respiratory infections, road injuries, interpersonal violence, tuberculosis, diabetes, ischemic heart disease, diarrhoeal diseases, stroke and premature birth complications. By 2040, however, diabetes will be the leading cause of death, followed by road injuries, lower respiratory infections, HIV/AIDS, interpersonal violence, ischemic heart disease, tuberculosis, chronic kidney disease, stroke and diarrhoeal diseases.

“The future of the world’s health is not preordained and there is a wide range of plausible trajectories,” said Dr Kyle Foreman, director of data science at the Institute for Health Metrics and Evaluation at the University of Washington and lead author on the study. “But whether we see significant progress or stagnation depends on how well or poorly health systems address key health drivers.”

The authors said there was huge potential to influence health through tackling high blood pressure, obesity, tobacco, alcohol and air pollution.

SA has implemented a variety of laws and regulations aimed at reducing noncommunicable diseases, ranging from tobacco controls to a tax on sugar-sweetened beverages. It has also moved to reduce the salt content in processed food.

“Understanding potential trajectories in health and drivers of health is crucial to guiding long-term investments and policy implementation,” said the authors. “Policy choices made today can profoundly affect each country’s future health trajectory. For most countries, prioritising noncommunicable diseases (NCDs) and NCD-related risks in health planning and investment decisions has the potential to markedly reduce premature mortality by 2040.”

The authors forecast 59 countries, including China, will surpass life expectancy of 80 by 2040. But Zimbabwe, Lesotho, Somalia and the Central African Republic will see life expectancy remain below 65 years, suggesting global disparities in health and survival are likely to persist.