The consequences of a low-dose Aspirin regimen for preventing conditions such as cancer and heart disease could outweigh the benefits for women under the age of 45.  

As women reach the age of 65 the balance between this shift starts to increase, and using this type of primary prevention in women of this age and older was determined to be better than not taking Aspirin at all, the BMJ-British Medical Journal reported.

To make their findings the researchers looked at 30,000 women who were at least 45 years old and taking part in the Women's Health Study. The participants were randomly assigned to take either 100 milligrams of Aspirin or a placebo every other day to see whether or not the drug reduced the risk of heart disease, stroke, or cancer.

Aspirin was found to reduce the risk of heart disease, stroke, and bowel cancer in some women, but these benefits were overshadowed by the prevalence of prevalence of internal gastrointestinal bleeding. This type of internal bleeding was found to affect two-thirds of the women who were on the placebo regimen.

The risk of gastrointestinal bleeding was found to rise with age, but so did the drug's effects on lowering bowel cancer and cardiovascular disease risk. The team calculated that over 15 years, 29 percent of over-65s would need to be treated with Aspirin in order to prevent cancer and heart disease.

"Recent findings that both daily and alternate day aspirin can reduce cancer risk, particularly for colorectal cancer, have re-ignited the debate on aspirin in primary prevention," the researchers wrote.  "[The treatment] is ineffective or harmful in the majority of women with regard to the combined risk of cardiovascular disease, cancer and major gastrointestinal bleeding."

The findings were published in a recent edition of the journal Heart.