Taking aspirin may have a protective effect against a number of cancers, a new study has suggested.

A trial involving more than 600,000 people found that long-term aspirin use appeared to reduce a person's risk of a number of digestive cancers, as well as leukaemia, lung and prostate cancer. 

It did not seem to have a protective effect for breast, bladder or kidney cancers.

The study saw researchers in Hong Kong compare cancer incidence among non-aspirin users and people who had been prescribed the drug for at least six months.

Researchers analysed data from all public hospitals in Hong Kong to compare information on 206,295 aspirin users - with an average of taking the medication for 7.7 years - and 412,589 non-aspirin users.

Patients were followed up for up to 14 years. Overall, 16% of people developed cancer.

Researchers found that long-term use of aspirin carried a "significant reduction" in the incidence of major gastrointestinal cancers.

Aspirin users were 47% less likely to have been diagnosed with cancers of the liver or oesophagus.

Experts also found significant reductions in the rate of stomach cancer, pancreatic cancer and bowel cancer with 38%, 34%, 24% reductions in incidence, respectively, among those who took the drug compared to non-aspirin users.

They also assessed cancers outside of the digestive system and found significant reductions in leukaemia, lung and prostate cancers among aspirin users.

Long-term aspirin users were 14% less likely to have developed prostate cancer, 24% less likely to have leukaemia and had a 35% reduced incidence of lung cancer.

"The findings demonstrate that the long-term use of aspirin can reduce the risk of developing many major cancers," said lead researcher Professor Kelvin Tsoi from the Chinese University of Hong Kong.

"What should be noted is the significance of the results for cancers within the digestive tract, where the reductions in cancer incidence were all very substantial, especially for liver and oesophageal cancer."

The study is to be presented to the United European Gastroenterology Week meeting in Barcelona.