Low-dose aspirin linked to anemia

Although daily, low-dose aspirin can help prevent heart attacks, this widely used drug comes with a downside: an increased risk of bleeding. This ranges from minor problems (such as noticeable bruising) to more serious but rare complications, such as bleeding in the brain.

New research now finds older people who take low-dose aspirin every day are more likely to develop anemia, a condition marked by a reduced amount of red blood cells. The findings are yet another reminder to be cautious about daily aspirin use. Although around half of older adults say they take low-dose aspirin, current guidelines recommend this practice only for people who have coronary artery disease or another vascular disease and for those who are under 70 and at high risk of a heart attack. (For more details, see "Advice about daily aspirin" in the July 2021 Heart Letter.)

"We can't talk about all the good that aspirin does without mentioning the potential harm," says cardiologist Dr. Gregory Piazza, associate professor of medicine at Harvard Medical School. Decades ago, doctors recommended low-dose aspirin for most men over 50, but that's no longer the case. Unless you have diagnosed cardiovascular disease, the risk of bleeding likely outweighs the drug's heart-protecting benefits, as several recent large studies comparing aspirin to a placebo have shown.

More harm than good

One of those studies was the ASPREE (Aspirin in Reducing Events in the Elderly) trial, which followed more than 19,000 initially healthy adults over age 70 for nearly five years. In these people, low-dose aspirin did not protect against heart attack or stroke. But it did raise the risk of major bleeding — especially in the stomach and brain — by 30%.

Aspirin may also cause subtle, undetected internal bleeding that leads to anemia, based on a new analysis of the ASPREE data that looked at participants' hemoglobin and ferritin levels, which were measured yearly. Hemoglobin carries oxygen in the blood; ferritin helps store iron in your body. Anemia is defined as having a hemoglobin level of less than 12 milligrams per liter (mg/L) for men and less than 11 mg/L for women.

This new analysis, published in the July 2023 Annals of Internal Medicine, found that people who took aspirin were 20% more likely to have anemia compared with those not taking the drug. Although mild cases of anemia might not cause any symptoms, the condition can lead to fatigue, weakness, shortness of breath, and dizziness, all of which result from the diminished oxygen levels in the body.

Aspirin's actions

Aspirin discourages blood clots by preventing tiny cell fragments in the blood called platelets from clumping together. But the drug also blocks substances that help maintain and protect the delicate tissue lining the gastrointestinal tract. "Long-term aspirin use can damage this protective layer, making bleeding more likely," says Dr. Piazza. Doctors refer to small amounts of bleeding as "occult" bleeding, since it often remains hidden and unrecognized.

This minor bleeding can occur in the stomach or farther down the gastrointestinal tract. If you have any sort of breach in this pathway, such as a hemorrhoid or a tiny colon polyp, taking daily aspirin can make it more likely to bleed. In fact, this phenomenon may explain why aspirin use has been linked to lower risk of death from colon cancer. Aspirin may reveal the cancer by causing a cancerous polyp to bleed and show up as blood in a person's stool. The resulting earlier diagnosis and treatment may extend survival, Dr. Piazza explains.

The bottom line

If you're currently taking low-dose aspirin, check with your doctor to make sure it makes sense for you. "With my patients, we review all their medications at every visit," Dr. Piazza says. People may have taken aspirin for years, but since bleeding risk rises with age, it might be time for them to stop. Or they may have started taking a different, more powerful clot-preventing medication that renders the aspirin unnecessary. A common example is clopidogrel (Plavix), which is often prescribed after a person gets an artery-opening stent.

If your doctor recommends low-dose aspirin, make sure you get an annual blood test that checks your hemoglobin levels. It's commonly done as part of an annual physical. But for heart disease prevention, doctors tend to focus on cholesterol and blood sugar values and may pay less attention to hemoglobin levels, says Dr. Piazza.

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