Aromatase inhibitors, including Arimidex (anastrozole), Femara (letrozole), and Aromasin (exemestane), inhibit the action of the enzyme aromatase, which converts androgens into estrogens by a process called aromatization. Aromatase inhibitors generally are used for estrogen receptor positive (ER+) breast cancer in postmenopausal women.
Whereas aromatase inhibitors block the production of estrogen, tamoxifen interferes with a tumor's ability to use estrogen. Both are designed to suppress ER+ breast cancer recurrence since estrogen promotes the growth of such cancer. Please see our articles on the impact of endocrine therapy on breast cancer prognosis and tamoxifen for more information.

Aromatase inhibitors are used for treating postmenopausal women

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 affect 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.

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:
Aromatase inhibitors should be taken at the same time every day. Arimidex and Femara can be taken with or without food. Aromasin should be taken after a meal to avoid nausea or indigestion. For the same reason, some women benefit from taking Aromasin at night.
Please read the applicable food pages when making your own food lists since these pages contain important advice, consumption limits, and other pertinent information.

Foods to avoid while taking aromatase inhibitors

The following have been found to increase aromatase or estrogen or to reduce the effectiveness of aromatase inhibitors and should be limited or avoided during treatment:
Note that exposure to cadmium has also been shown to reduce the effectiveness of aromatase inhibitors.

Supplements during aromatase inhibitor treatment

There is no supplement or combination of supplements that has been proven to reliably reduce the risk of ER+ breast cancer recurrence in women. 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 a high dose in a supplement, it is more likely to have pharmacological effects, with mostly unknown results. It is best to obtain beneficial compounds by consuming food, if possible. Supplements make sense if medically necessary or to make up for deficiencies that are difficult to correct through diet.
The supplements below generally been found to be safe and beneficial for patients taking aromatase inhibitors:
SupplementDosage
CoQ10 (if needed for heart health)100 to 400 mg/day
Fish oil (from wild-caught fish)1000 to 2000 mg/day
Vitamin D1000 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 tests to determine if your reading has reached a desirable level.

Supplements to avoid while on aromatase inhibitors

The supplements below have been reported specifically to increase estrogen or aromatase activity, or else to reduce the effectiveness of aromatase inhibitors or increase their side effects. 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.
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 can reduce some aromatase inhibitor side effects

To varying degrees, women taking aromatase inhibitors experience menopausal symptoms such as increases in joint disorders, bone fractures, and vaginal/urogenital atrophy, in addition to weight gain and higher cholesterol (especially for those switching from tamoxifen). Please see our article on aromatase inhibitor-associated weight gain. Weight gain after diagnosis has been shown to increase hot flashes in breast cancer survivors using aromatase inhibitors. There are some foods that can reduce menopausal side effects while at the same time reducing the risk of breast cancer recurrence.

Foods that safely reduce aromatase inhibitor side effects

The following foods (or major components) have been shown to safely reduce some of the side effects of aromatase inhibitors:
Moderate to vigorous physical activity, particularly aerobic exercise, has been shown to be associated with lower risk of bone fractures in women being treated with aromatase inhibitors. Aspirin appears to be safe to take for pain 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.
The estrogen deprivation caused by aromatase inhibitors can cause chemo brain symptoms in some women. Such mild cognitive impairment appears to improve within a year after endocrine treatment ends (chemo brain may last longer if chemotherapy was also part of breast cancer treatment). One major 2021 study found no links between use of endocrine treatments in non-metastatic breast cancer and risk of subsequent dementia.
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 (but not during treatment).

Foods and beverages that might worsen side effects

The following should be limited during aromatase inhibitor treatment since high consumption could contribute to bone loss:
One study reported that aromatase inhibitor-induced bone loss appears to be partially reversible after treatment is completed.

Sources of information provided in this webpage

This webpage lists foods that inhibit aromatase and/or enhance the treatment effects of aromatase inhibitors. It also lists foods, supplements and other exposures that should be limited since they can increase aromatase or otherwise interfere with aromatase inhibitor treatment.
The food lists, which are updated continually as new research becomes available, have been developed based solely on the results of academic studies. Clicking on any of the foods will take you to its webpage, which contains specific information concerning that food's relationship to breast cancer (including its overall ranking, for example, highly recommended or recommended in moderation), as well as links to supporting studies.
For a list of foods that naturally inhibit aromatase, see Foods that act as aromatase inhibitors. Note that not all foods that inhibit aromatase are safe to consume during aromatase inhibitor treatment.

Additional comments

We suggest that estrogen sensitive breast cancer patients and survivors consume a wide variety of the foods from our recommended list and restrict those on our limit or avoid list. This is in addition to paying attention to the foods, spices and supplements on the lists above. 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 20 recent studies concerning aromatase inhibitor treatment. See also the aromatase inhibitors tag and Foods that increase or reduce aromatase activity.