Aromatase inhibitors are designed to inhibit the action of the enzyme aromatase, which converts androgens into estrogens by a process called aromatization. Aromatase inhibitors include Arimidex (anastrozole), Femara (letrozole), and Aromasin (exemestane). Aromatase inhibitors generally are used for estrogen receptor positive (ER+) breast cancer in postmenopausal women. Since the growth of ER+ (i.e., estrogen sensitive) breast cancer is promoted by estrogen, decreasing the production of estrogen in the body is designed to suppress recurrence. There are also some foods that inhibit aromatase and other foods that increase aromatase or otherwise interfere with aromatase inhibitors.
Note that whereas aromatase inhibitors block the production of estrogen, tamoxifen interferes with a tumor's ability to use estrogen. Please also see our article on the impact of endocrine therapy on breast cancer prognosis.
Aromatase inhibitors normally are not used to treat breast cancer in premenopausal women unless accompanied by ovarian function suppression. This is because inhibiting aromatase does not effect the production of estrogen by the ovaries, which are the most abundant source of estrogen in premenopausal women. To the extent that an aromatase inhibitor did decrease the production of estrogen in a premenopausal woman, the decrease would tend to stimulate the ovaries to increase androgen production, thereby neutralizing the effect of the aromatase inhibitor.
To varying degrees, women taking aromatase inhibitors experience side effects such as increases in joint disorders, bone fractures, vaginal/urogenital atrophy, and cholesterol (especially for those switching from tamoxifen). Weight gain after breast cancer diagnosis has been shown to increase hot flashes in breast cancer survivors on aromatase inhibitors. There are some foods that can reduce these side effects while at the same time reducing the risk of a breast cancer recurrence.

Foods that enhance the effectiveness of aromatase inhibitors

The following foods (or major bioactive components) have been found to inhibit aromatase or to enhance the effectiveness of aromatase inhibitors and are recommended during treatment:

Foods to avoid while taking aromatase inhibitors

The following have been found to increase aromatase or reduce the effectiveness of aromatase inhibitors and should be limited or avoided during treatment:

Supplements for patients being treated with an aromatase inhibitor

There is no supplement or combination of supplements that has been shown to reduce the risk of ER+ breast cancer recurrence. Attempting to increase the treatment effects of micronutrients and other dietary components by using supplements carries the risk of adverse and paradoxical effects, including promoting breast cancer growth and metastasis.
What is known is that when a beneficial micronutrient is administered at low doses by consuming food, it is likely to have subtle chemopreventive effects, whereas when the same micronutrient is administered at high doses, it is more likely to have pharmacological effects, with mostly unknown results. It is best to obtain beneficial compounds by consuming food, if possible. The role of supplements is to make up for deficiencies that are difficult to correct through diet.

Supplements for AI patients

The supplements below generally been found to be safe and beneficial for patients taking aromatase inhibitors:
Supplement → Approximate dosage
CoQ10 (only if needed for heart health) → 100 to 400 mg/day
Fish oil → 1000 to 2000 mg/day
Vitamin D → 1000 to 2000 IU/day
Please consult your oncology team for advice concerning your situation and dosages. It might make sense to be tested for deficiency in vitamin D and plan for follow up to determine if your reading has reached a desirable level.

Supplements and other to avoid while taking aromatase inhibitors

The supplements below have been found to increase aromatase or reduce the effectiveness of aromatase inhibitors and should be avoided during treatment. That is not to say that most other supplements are safe to take; there are no relevant scientific studies concerning the interactions between most supplements and aromatase inhibitors.
Apigenin supplements
Astragalus or huang qi supplements
Copper & multivitamins with copper
Genistein, daidzein or equol supplements
Goldenseal supplements
HRT, combined (estrogen plus progestin), including bioidentical hormones
Licorice root supplements
Milk thistle supplements
Propolis or royal jelly supplements
Quercetin supplements
Red clover supplements
Rhein supplements
Reishi mushroom supplements (ok for IBC)
Sage supplements & sage essential oil
St. John’s wort supplements
Turmeric or curcumin supplements
Cigarette smoking has also been found to sharply reduce the effectiveness of treatment with aromatase inhibitors. The heart medication digoxin has also been shown to have estrogenic effects that could potentially interfere with aromatase inhibitor treatment.

Foods that safely reduce the side effects of aromatase inhibitors

The following foods (or major components) have been shown to help reduce the side effects of aromatase inhibitors:
Aspirin appears to be safe to take during aromatase inhibitor treatment. Women should not use copper bracelets or copper compression garments to relieve arthritis pain. Copper has been shown to contribute to angiogenesis and metastasis of breast cancer.
Low-dose vaginal estrogen, which is used to relieve vaginal dryness and related urogenital atrophy, appears to be safe for use for postmenopausal women after aromatase inhibitor treatment has been completed.

Foods and beverages that might worsen side effects of aromatase inhibitors

The following should be limited during aromatase inhibitor treatment since high consumption could contribute to bone loss:

Additional comments

We suggest that estrogen sensitive breast cancer patients and survivors to eat a wide variety of the foods from our recommended list and limit or avoid those on our avoid list, in addition to paying particular attention to the foods, spices and supplements on the lists above. Note that weight gain during aromatase inhibitor treatment has been found to be associated with less favorable prognosis. Please see our article on how to optimize your breast cancer diet for information on what to eat during all stages of treatment and recovery.
Below are links to recent studies on aromatase inhibitor treatment. See also the aromatase inhibitors tag and Foods that increase or reduce aromatase activity.