More than 2.7 billion people including children have been exposed to second-hand smoke globally, contributing to nearly 1.7 million deaths in 2023, according to study published Tuesday in The Lancet.

Tobacco remains a leading cause of disease globally, the study said, noting many "non-smokers exposed to second-hand smoke" were among the estimate total of 8 million people who died in 2023 of smoking-related illnesses.

"Exposure to second-hand smoke is a globally recognised health risk, with no safe level of inhalation," it said.

By reviewing studies published in the US National Institutes of Health database PubMed along with population surveys, Tuesday's study sought to estimate the prevalence of exposure to second-hand smoke and quantify the burden of disease in 204 countries and territories between 1990 and 2023.

Among the approximately 2.7 billion people exposed to second-hand smoke in 2023 were 767 million children aged 0 to 14, the study found.

This exposure is estimated to have resulted in 1.66 million premature deaths and causing premature disability and illness, leading with ischemic heart disease, a heart condition caused by insufficient oxygen supply to the heart muscle.

In children, exposure to second-hand smoke is estimated to have caused 5.2 million respiratory tract infections in 2023, it said.

People in proximity to someone lighting up are exposed to both the "sidestream smoke" from the burning tobacco product and smoke exhaled by the active smoker, the study explained.

"The sidestream component, which dominates the air non-smokers breathe, is unfiltered... carrying higher per-unit concentrations of the toxic and carcinogenic compounds" than that being inhaled by the active smoker, it said.

Despite significant declines in smoking prevalence globally since 1990, the absolute number of people exposed has remained stable due to population growth and increased exposure in Africa and the Middle East.

Women are also disproportionately affected by second-hand smoke, particularly in regions where smoking prevalence among women is low, it noted.

"Despite this substantial burden, (second-hand smoke) exposure remains rarely acknowledged as a major risk factor for female health," it said.

The study called for governments to implement stronger tobacco controls in public places and in homes in order to better protect women and children from second-hand smoke.