The number of smokers worldwide increased to 1.1 billion in 2019, with tobacco smoking causing 7.7 million deaths - including one in five deaths in males worldwide.

Researchers say the global number of smokers continues to rise, and there is particular concern over persistently high rates of smoking among young people.

Given that the large majority of new smokers become addicted by age 25, protecting young people from nicotine addiction during this window will be crucial to eliminate tobacco use among the next generation, experts suggest.

Using data from 3625 nationally representative surveys, the three studies are published in The Lancet and The Lancet Public Health journals by the Global Burden of Disease collaboration.

They provide global estimates on smoking prevalence in 204 countries in men and women aged 15 and over.

This includes age of initiation, associated diseases, and risks among current and former smokers, as well as the first analysis of global trends in chewing tobacco use.

Published ahead of World No Tobacco Day on May 31, the authors call on all countries to urgently adopt and enforce a package of evidence-based policies to reduce the prevalence of tobacco use and prevent initiation at a young age.

Researchers found that since 1990, global smoking prevalence among men decreased by 27.5 per cent and by 37.7 per cent among women.

The 10 countries with the largest number of tobacco smokers in 2019 - comprising nearly two thirds of the global tobacco smoking population - are China, India, Indonesia, the USA, Russia, Bangladesh, Japan, Turkey, Vietnam, and the Philippines.

One in three current tobacco smokers (341 million) live in China, researchers found.

Researchers found that in 2019, smoking was associated with 1.7 million deaths from ischaemic heart disease and 1.6 million deaths from chronic obstructive pulmonary disease.

It was also associated with 1.3 million deaths from tracheal, bronchus, and lung cancer, and nearly one million deaths from stroke.

Previous studies suggested that at least one in two long-term smokers will die from causes directly linked to smoking, and that smokers have an average life expectancy 10 years lower than never-smokers.

The data also indicates that approximately 87 per cent of deaths attributable to smoking tobacco occurred among current smokers.

Only six per cent of global deaths attributable to smoking tobacco use occurred among individuals who had quit smoking at least 15 years previously.

Researchers say this highlights the importance of quitting.

In 2019, there were an estimated 155 million smokers aged between 15 and 24 - equivalent to 20.1 per cent of young men and five per cent of young women, globally.

Two thirds (65.5 per cent) of all current smokers began smoking by the age of 20, and 89 per cent of smokers began by age 25.

But globally, smoking prevalence among young people decreased between 1990 and 2019 among both young men (minus 32.9 per cent) and young women (minus 37.6 per cent).

The authors note limitations across the three studies, including that data on tobacco use are self-reported, age of initiation may be subject to recall bias, and the health effects of smoking do not include second-hand smoke.

Australian Associated Press