Coffee is one of the most popular beverages worldwide. More than 30 percent of breast cancer survivors report drinking a lot of coffee or tea after a breast cancer diagnosis.

If you’re a coffee lover, you may wonder how your coffee consumption may affect your prognosis (expected outcome) and treatment with triple-negative breast cancer (TNBC). TNBC is an aggressive subtype of breast cancer in which breast cancer cells lack estrogen or progesterone receptors and don’t make much of a protein called HER2. Between 10 percent and 15 percent of all breast cancers are TNBC, according to the American Cancer Society.

In general, making healthy lifestyle changes can decrease your risk of breast cancer recurring (coming back) and improve your chances of survival. But how does this approach apply to a coffee habit? Continue reading to learn more about coffee’s potential effects on TNBC.

1. Drinking Coffee May Lower the Risk of Breast Cancer

It may be cold comfort if you’re already diagnosed with TNBC, but several studies have linked drinking coffee with a decreased risk of developing breast cancer.

An international study in the journal Nutrients found that among women who’d gone through menopause, coffee drinkers had a lower risk of all types of breast cancer. In a large study in Sweden, drinking at least 3 cups of coffee per day was associated with a lower risk of being diagnosed with breast cancer.

A study of more than 335,000 European women, published in British Cancer Research, also linked drinking caffeinated coffee with a lower risk of breast cancer in postmenopausal women. The researchers noted that they didn’t find an association between decaffeinated coffee (decaf) and breast cancer. Their results suggest that compounds specifically in caffeinated coffee may be responsible for the reduced risk.

In a 2011 study, drinking coffee was associated with a lower risk of estrogen receptor (ER)-negative breast cancer but didn’t show the same protective benefits with ER-positive breast cancer. Researchers questioned if some compounds found in coffee may stimulate ER-positive cancer cells, decreasing coffee’s protective effects for ER-positive cancer. Other compounds in coffee are associated with a lower risk of ER-negative breast cancer.

These studies indicate that drinking coffee, in large volumes or caffeinated, may help reduce the overall risk of breast cancer. Researchers aren’t sure why coffee may offer this benefit but believe that it might:

• Act as an antioxidant (a substance that prevents cell damage)
• Reduce inflammation
• Decrease insulin resistance (when cells don’t respond to the hormone insulin)

2. Caffeine Can Interact With Some Treatments for Triple-Negative Breast Cancer

It’s easy to forget that caffeine is a drug — it’s the active ingredient that’s responsible for coffee’s stimulant effect. Within five to 30 minutes after you’ve had a cup of coffee, caffeine can start to affect your body, including:

• Heart rate
• Breathing rate
• Mental alertness
• Physical energy

Like other drugs, caffeine can potentially interact with medications, such as chemotherapy (chemo) for TNBC.

Researchers looking at TNBC cells in a U.S. laboratory found that caffeine may boost the effects of the chemotherapy drug cisplatin, a TNBC treatment option. However, more research is needed to understand the effect of combining caffeine and chemo drugs, like cisplatin, in humans.

Although there’s some evidence that caffeine may help some chemo drugs work, it may interact negatively with others. A MyBCTeam member warned other members, “If you check on Taxol, it says caffeine may interfere with the effects of that chemo.”

Paclitaxel (available as Abraxane and formerly sold as Taxol in the U.S.) is a first-line treatment (first recommended treatment) for TNBC. Studies have found that consuming caffeine while on paclitaxel may inhibit the drug’s ability to kill cancer cells.

Ask your cancer care team if your TNBC treatment has any potential dietary interactions. For instance, are there recommendations against drinking coffee, or are there any foods you should avoid?

3. Drinking Coffee Doesn’t Worsen Your Outcome

If you’ve been diagnosed with TNBC, you may wonder if drinking coffee during your treatment can change your prognosis. Studies have found that, in general, drinking coffee after a breast cancer diagnosis isn’t associated with a worse outcome.

A 2021 British Journal of Cancer study that followed 8,900 women with stage one to three breast cancer linked drinking more than 3 cups of coffee a day with a lower risk of dying from breast cancer or any other cause. In a 2022 study of more than 3,700 people with stage one to three breast cancer, researchers found that drinking over 3 cups of coffee or tea a day wasn’t associated with worse survival outcomes. Limited studies about coffee have included participants with stage four breast cancer.

4. Coffee May Help — or Worsen — Side Effects of TNBC Treatment

Chemotherapy is the main treatment for TNBC. Although side effects differ for everyone, common side effects of chemo include:

• Hair loss
• Nail changes
• Mouth sores
• Decreased appetite and weight loss
• Nausea, vomiting, and diarrhea
• Fatigue
• Menopausal symptoms (such as hot flashes and vaginal dryness)
• Nerve damage

Some MyBCTeam members have described how drinking coffee helped with chemo side effects. One said, “I gave up caffeinated coffee, except occasionally, about a year before my diagnosis. I discovered quickly that one cup a day on no chemo days is the best way for me to fight the morning fatigue and get me moving.”

Another member shared, “I’ve been in chemo for over a year. The side effects are terrible! I get dizzy, nauseous, irritated, etc.! Drinking iced coffee helps my mood. Always decaf!”

While caffeine can help ease fatigue by increasing mental and physical energy, you should be aware of the possible side effects of high caffeine consumption, such as:

• Dehydration
• Nausea
• Dizziness
• Headache
• Rapid heart rate
• Restlessness
• Anxiety
• Poor sleep

Some side effects of caffeine may make chemo side effects worse. For example, staying hydrated during chemotherapy is often recommended to manage side effects. If you drink too much caffeine, which can have a diuretic effect (making you pee more often), you may get more dehydrated. Other side effects of caffeine may overlap with chemo side effects, such as nausea and dizziness.

According to the U.S. Food and Drug Administration (FDA), a daily caffeine intake of up to 400 milligrams — the amount in about 4 cups of coffee — is safe for most healthy adults. Talk to your cancer care team about how much caffeine is safe for you to drink each day with your TNBC treatment regimen.

5. Coffee Consumption May Reduce the Risk of Other Cancers

Some breast cancer survivors have a higher risk of developing a second type of cancer. The specific type depends on several risk factors, such as genetics, family history, and the type of TNBC treatment received.

Healthy lifestyle changes such as eating a balanced diet, engaging in physical activity, avoiding tobacco, and limiting alcohol are important for cancer prevention.

Cancer research studies have also linked coffee consumption to a decreased risk of certain cancers, such as:

• Liver cancer
• Endometrial (uterine) cancer
• Oral (mouth and throat) cancers
• Prostate cancer

If you’re concerned about increased risk factors for developing second cancers, talk to your cancer care team.

Find Others Who Understand

MyBCTeam is the social network for people with breast cancer and their loved ones. On MyBCTeam, more than 67,000 members come together to ask questions, give advice, and share their stories with others who understand life with breast cancer.

How much coffee do you drink? Has drinking coffee helped with any chemo side effects or made others worse? Share your experiences in the comments below, or start a conversation by posting on your Activities page.