It wasn’t that long ago that doctors advised taking a low dose aspirin a day as a preventive against heart attacks. Then, new studies found the risk of aspirin-induced internal bleeding outweighed any benefits it might confer, except in older patients at risk of heart problems.

Yet, there’s still enough uncertainty about the overall preventive benefits that the U.S. Preventive Services Task Force gives that recommended use a grade of B, and says there’s just not enough evidence to decide aspirin’s benefit for younger people. Just last week, the U.S. Preventive Services Task Force issued a final research plan on aspirin use to prevent cardiovascular disease and colorectal cancer.

But now one of the largest and most comprehensive studies reports that aspirin can reduce the risk of digestive tract cancers between 22% and 38%.

Researchers analyzed of 113 observational studies investigating cancers in the general population published up to last year, finding that regular use of aspirin significantly reduced the risk of most types of digestive tract cancers, including liver and pancreatic cancers that are almost always fatal.

Published last month in the Annals of Oncology, the report found aspirin use was linked to:

  • 27% reduced risk of bowel cancer;
  • 33% reduced risk of oesophageal cancer;
  • 39% reduced risk of gastric cardia (a part of the stomach);
  • 36% reduced risk of stomach cancer;
  • 38% reduced risk of liver, gallbladder and bile duct cancer;
  • 22% reduced risk of pancreatic cancer.

In an article for ESMO, the oncology professional organization, Dr. Cristina Bosetti (PhD), head of the unit of cancer epidemiology at the Mario Negri Department of Oncology in Milan, said, it appears that the higher aspirin doses the greater the decreased risk.

“We found that the risk of cancer was reduced with increased dose; an aspirin dose between 75 and 100mg a day was associated with a 10% reduction in a person’s risk of developing cancer compared to people not taking aspirin; a dose of 325mg a day was associated with a 35% reduction, and a dose of 500mg a day was associated with a 50% reduction in risk. However, the estimate for high dose aspirin was based on just a few studies and should be interpreted cautiously.

“Our findings on bowel cancer support the concept that higher aspirin doses are associated with a larger reduction in risk of the disease. However, the choice of dose should also take into consideration the potential risk of stomach bleeds, which increases with higher aspirin doses.”

As strong as the results are, the analysis is based on observational studies, meaning the researchers in each of the 113 studies simply collected data from the subjects and reported on the outcome. It’s possible that other factors may have influenced the results of some or all of the 113 studies.

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