Breast Cancer Risk Factors – New Findings

Antibiotics increase it, NSAIDs decrease it.

Long-term use of antibiotics is associated with an increased risk of breast cancer, while long-term use of NSAIDs (ibuprofen, aspirin) is associated with a decreased risk of breast cancer.

The association between antibiotics and breast cancer was discovered about 20 years ago, but up until recently it hasn’t been well studied. Researchers from the University of Washington in Seattle compared women who had invasive breast cancer with women who didn’t. They found that when all days of antibiotic use were added up, the more days a woman used antibiotics, the greater her risk of breast cancer. For example, women who used antibiotics for 51 to 100 days had 1.53 times the risk of breast cancer, and women who used them from 100 to 500 days had 1.68 times the risk of breast cancer. For women who used antibiotics for 501 to 1000 days, the risk jumped to 2.14 times.

An earlier study in Finland found an increased risk of breast cancer among women who habitually used antibiotics to treat urinary tract infections.
The researchers of the Seattle study hasten to add that this doesn’t prove antibiotics directly cause breast cancer: women who use antibiotics may have underlying illnesses that would predispose them to breast cancer. However, in an article published in Cancer Causes and Control in 2003, a group of researchers theorized that antibiotics kill beneficial bacteria in the gut that play an important role in protecting the body against excess estrogen and the more harmful forms of estrogen. They also hypothesize that antibiotics may increase breast cancer risk because they inhibit key parts of the immune system that protect against cancer, as well as anti-inflammatory mechanisms.

A Cautionary Tale
This research gives us yet another reason to avoid using antibiotics unless absolutely necessary. If you must use them, be sure to use plenty of probiotics to replace gut bacteria (e.g. eat live culture yogurt or get probiotic supplements).

Anti-inflammatories and Breast Cancer
Inflammation is one of the pieces of the breast cancer puzzle, and that may be why other research is showing that nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and aspirin, may help prevent breast cancer. This information came out of the Women’s Health Initiative (WHI), a large, ongoing, government-sponsored study of women’s health in the U.S. (The WHI is best known for the revelation a few years ago that conventional HRT increases the risk of breast cancer, stroke, heart disease and gallbladder disease.)

The NSAIDs arm of the WHI study compared nearly 80,000 women who didn’t have breast cancer, to 1,392 who did, and looked at how often they took NSAIDs. They found that women who took 2 or more tablets per week of over-the-counter anti-inflammatory drugs at standard doses for 5 to 9 years, had 21 percent less risk of breast cancer. Protection went up to as much as 28 percent for women who had used NSAIDs for more than 10 years, and who had used ibuprofen instead of aspirin. Low dose aspirin and the pain reliever acetaminophen (e.g. Tylenol) did not protect against breast cancer, which makes sense because acetaminophen is a pain killer but not an anti-inflammatory.

What Does All This Mean to You?
Before you run to the drugstore for ibuprofen, remember that regular use of NSAIDs is associated with gastrointestinal bleeding and kidney problems—these aren’t drugs that you want to be taking on a regular basis unless you have to, especially if you have a tendency to have digestive or kidney problems. However, taking a couple of tablets a week is unlikely to be harmful to most people, and might help some.

More direct and effective ways to prevent breast cancer include maintaining hormone balance with natural, bioidentical hormones and lifestyle factors such as getting plenty of exercise and eating plenty of fruits and vegetables.

For details on hormone balance and how inflammation contributes to breast cancer, please read What Your Doctor May Not Tell You About Breast Cancer. This study is also is a good indicator that it might be helpful in the long run to reduce inflammation. There are a lot of pointers for reducing inflammation without NSAIDs in the book Prescription Alternatives.


Velicer CM, Heckbert SR et al, “Antibiotic use in relation to the risk of breast cancer,” JAMA 2004 Feb 18;291(7):827-35.

Velicer MV, Lampe JW et al, “Hypothesis: is antibiotic use associated with breast cancer?” Cancer Causes and Control 2003, 14:739-747.

Moorman PG, Grubber JM, “Association between non-steroidal anti-inflammatory drugs (NSAIDs) and invasive breast cancer and carcinoma in situ of the breast,” Cancer Causes Control, 2003 Dec;14(10):915-22.

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