A large study shows that daily low-dose aspirin might lower the risk of certain cancers. But doctors caution that this doesn’t necessarily mean you should start taking aspirin.

Long-term aspirin use may lower the risk of developing digestive cancers, according to a new study.

The research was presented last week at the 25th UEG (United European Gastroenterology) Week in Barcelona.

The large-scale study involved more than 618,000 people.

Of those, more than 206,000 were aspirin users with a mean age of 67 years. They took a mean dose of 80 milligrams (mg) for at least six months. The average length was 7.7 years.

A second group was made up of more than 412,000 people who did not use aspirin. They also had a mean age of 67 years.

The researchers compared the two groups over a span of 10 years.

In the aspirin group, there was a noteworthy reduction in the incidence of five kinds of digestive cancer.

The biggest reductions were for liver and esophageal cancer. Both were reduced by 47 percent.

The incidence of gastric cancer was reduced by 38 percent. For pancreatic cancer, it was 34 percent. Colorectal cancer was reduced by 24 percent.

“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, PhD, of 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 esophageal cancer,” he added.

Dr. Jason A. Zell is director of the Hematology/Oncology Fellowship Program and assistant professor in the departments of medicine and epidemiology at the University of California, Irvine.

He notes that this research was an observational study.

“Aspirin use was recorded, but not randomly assigned in a prospective manner (as would be done in a randomized controlled clinical trial),” Zell told Healthline.

That’s not enough to change clinical practice, he concluded.

“I believe the existing USPSTF [U.S. Preventive Services Task Force] guidelines properly balance the risks vs. benefits of aspirin use in the primary prevention setting,” Zell explained.

Under current guidelines, low-dose aspirin is indicated for prevention of cardiovascular disease and colorectal cancer.

But only for certain groups.

“This recommendation is given a category ‘B’ rating and is limited only to those age 50 to 59 years and without bleeding risk,” cautioned Zell. “For individuals age 60 to 69, USPSTF gives a ‘C’ rating. And for those under age 50 years or over age 70 years, USPSTF gives an ‘I’ rating, indicating insufficient evidence.”

Zell said the preventive effects of aspirin apply to men and women.

When it comes to cancer prevention, though, age is an issue.

“Most studies demonstrate cancer preventive benefits only after taking a prolonged course of daily aspirin (i.e., 10 years or greater),” he said. “For that reason, the benefit of aspirin decreases with age, as indicated in the USPSTF guidelines.”

Dr. Andrew Coveler is a medical oncologist who treats cancers of the gastrointestinal system. He’s also the director of the Pancreatic Cancer Specialty Clinic at Seattle Cancer Care Alliance.

“Aspirin has been shown in several studies to reduce the incidence and severity of GI cancers,” he told Healthline. “This adds to the data indication that aspirin may benefit people to decrease the risk of various cancers.”

It’s more data, but it doesn’t necessarily mean anything should change just yet.

Coveler noted that this was a retrospective study of people in Hong Kong. So, it’s not clear if the same is true for other populations.

“In people who have had a heart attack or stroke, or other forms of cardiovascular disease, low-dose aspirin significantly reduces the risk of having another heart attack or stroke, or of dying from cardiovascular disease,” said Coveler.

How does it work?

Zell explained that aspirin inhibits prostaglandin synthesis. It has to do with biochemical substances involved in the inflammatory response.

Simply put, it’s an anti-inflammatory agent.

“Which explains its role in colorectal prevention (since there is a link between inflammation and dysplasia, cancer formation a.k.a. carcinogenesis),” said Zell.

Aspirin also stops blood from clotting.

“The cardiovascular disease protection ascribed to aspirin is related to both the anti-inflammatory and anti-platelet actions of aspirin. Since cardiovascular disease and cancer are the two most common causes of mortality in the U.S., aspirin has been investigated extensively in the prevention arena,” added Zell.

But there’s a downside to aspirin. The anti-clotting action is dangerous for some people.

“Aspirin inhibits platelet function, which decreases clot formation, but also may lead to clinical bleeding. Patients that are at a risk for bleeding should avoid aspirin. As should patients that are already taking other forms of blood thinners,” he said.

When it comes to taking daily aspirin, there’s no blanket rule.

“As an oncologist,” said Coveler, “my patients have a history of cancer. I do try and discuss the risks and benefits of aspirin and colon cancer prevention and recurrence.”

Still, he warns against starting a daily aspirin regimen on your own. It’s worth having the discussion with your doctor.

Zell agrees.

“It’s important to remember that when making decisions about preventing a disease in healthy patients, there is a very low threshold for adverse events. In other words, we must use caution recommending any drug to healthy patients. Even a small rate of adverse side effects could have a large effect when applied broadly to the U.S. population,” he said.

“In this regard, it is clear that aspirin cannot be used for primary prevention for everyone. Potential benefits may be seen in specific groups, if the risks of adverse effects (e.g., bleeding) are low,” he added.

“I would advise patients to talk with their doctor before using aspirin for primary prevention of cardiovascular disease or cancer. This should lead to a review of current guidelines and evaluation of patient-specific risks and benefits. That will help patients make an informed decision,” said Zell.