Nearly half of cancers worldwide can be traced back to a known risk factor, primarily tobacco or alcohol, a huge global study found on Friday, which said that behavioural changes can help reduce the threat of disease.

The study -- published in the Lancet and conducted as part of a vast research programme funded by the Bill Gates Foundation -- concluded that 44.4 percent of cancer deaths worldwide were attributable to a known risk factor.

The Global Burden of Disease Study is a comprehensive regional and global research programme involving thousands of researchers from most countries across the world.

The study analysed the impact of 34 risk factors and confirmed what is already widely known -- that tobacco is by far the biggest contributory factor to cancer, accounting for 33.9 percent of cases, followed by alcohol with 7.4 percent.

More than half of all male cancer deaths were attributable to such risk factors, and over a third of female deaths, the study found.

And since "the leading risk factors contributing to global cancer burden in 2019 were behavioural... reducing exposure to these modifiable risk factors would decrease cancer mortality" worldwide, the study concluded.

That also meant greater emphasis should be placed on prevention, the study found.

"The burden of cancer remains an important public health challenge that is growing in magnitude around the world," said Christopher Murray, director of the Institute for Health Metrics and Evaluation at the University of Washington's School of Medicine and a co-senior author of the study.

"Smoking continues to be the leading risk factor for cancer globally, with other substantial contributors to cancer burden varying."

However, around half of cancers are not attributable to a known risk factor, meaning early diagnosis and effective treatments must accompany efforts to raise prevention efforts, the study found.