Supplements During Breast Cancer Treatment: Important Update

Dietary supplements during breast cancer treatment can seem like a savvy strategy, but many women are unaware that supplements may interfere with breast cancer therapy.

Supplements – especially vitamins and botanical products – often have a sort of halo:

“How could it hurt?”

But although herbal and other botanical products may seem like promising ways to improve outcomes or to deal with unwanted side effects of cancer or its treatment, research points to many with potential for interactions with cancer treatment (and other medications).

Why Supplements Can Interfere with Hormonal Therapy

Here’s Part One of my interview with Maura Harrigan, MS, RDN, CSO.

Listen as she describes findings from her research on supplement use in women on adjuvant hormonal therapy for breast cancer.

In this video:

• Background and Introduction to the Issue       00:01
• The Research: How Big is This Problem?       01:00
• Why “Natural” and “Botanical” Do Not Signal Safety       03:36

Complexities of Supplements During Breast Cancer Treatment

Studies have previously documented that many people who’ve been diagnosed with cancer take dietary supplements, both during and after treatment – often without discussing it with their healthcare providers. The study that Maura Harrigan, MS, RDN, CSO, discusses in the video here went a step further and asked women on adjuvant hormone therapy for breast cancer about the number of supplements used… and then looked more specifically at whether this can be assumed to be harmless.

Of the 475 women on adjuvant hormone therapy in this study:

• 83% reported using dietary supplements.
• More than half were taking three or more supplements, and nearly a quarter taking five or more.
• Of the 108 different types of supplements reported, about 1 in 3 had potential interactions with tamoxifen or an aromatase inhibitor.

Examples of Supplements that May Interact with Hormone Therapy

Tamoxifen and specific aromatase inhibitors are processed differently in the body, and may differ in how they interact with dietary supplements.

The study of women on adjuvant hormone therapy for breast cancer discussed here focused on supplements that the Natural Medicines Database (see Resources) identified with potential for major or moderate interactions with hormone therapy. Women in this survey reported use of 36 such supplements.

The article includes a complete list of supplements identified. Here are a few examples:

• Ginseng
• Grapeseed
• Green tea extract
• Milk thistle
• Resveratrol
• Sulforaphane
• Turmeric extract
• Vitamin E

Since healthcare providers are often unaware of a patient’s supplement use, these interactions with treatment may be going on unrecognized.

Don’t assume that because a product is available that it must be safe. Unlike medications, dietary supplements do not have to provide proof of safety. Surveys, and my own experience talking with clients over the years, show that many people (and some health professionals) are unaware of this. The U.S. Food and Drug Administration (FDA) offers clear warnings about this, so check the Resources section if you want to learn more.

Risk from Supplements During Breast Cancer Treatment: 2 Key Cautions

Here’s Part 2 of our conversation:

In this video:

• The Counterintuitive Ways that Dose Matters       00:01
• Stacking: The Overlooked Risk       02:00
• Advice on Smart Steps       06:17

We need to break the mindset that if some is good, more is better.

As Maura Harrigan explains in our interview, potential for a supplement to interact with hormonal therapy (or any medication) increases with high doses within a product or stacking of multiple compounds that interfere with the same metabolic pathway.

Note carefully: Foods that are naturally “high” in compounds like those listed above in supplements of concern are not a risk during hormone therapy. As discussed in the second video here, foods that are relatively high in these compounds (like broccoli providing sulforaphane and grapes providing resveratrol) compared to other foods don’t provide the high doses found in isolated supplements. As Ms. Harrigan emphasizes, a variety of different plant foods provide a wide range of compounds that can work together.

More is not always better… and it may pose risk.

Identification of possible risks is especially difficult because of unknown contents and amounts in proprietary botanical blends.

Make This Less Daunting

It is important for people going through cancer treatment to be mindful of the potential for dietary supplements to interact with medications.

Rather than making suppositions about which supplements are or are not relevant to medical care, people using supplements should make a complete list and provide it to their full healthcare team (all their physicians and their oncology pharmacist and dietitian).

Ultimately, the best starting point is with meals and snacks that are centered as much as possible around whole, nutrient-rich plant foods.

Studies are clear that eating choices don’t need to be perfect to support health. When food preparation or eating is difficult, each step forward helps.