Tamoxifen (Nolvadex) is effective in preventing and treating estrogen receptor-positive (ER+) breast cancer. Women who complete their prescribed anti-estrogen treatments have been found to have better recurrence and survival profiles than women who do not. There are some foods that appear to enhance the effectiveness of tamoxifen treatment and others that reduce it.

Tamoxifen is associated with higher risk of endometrial cancer for women who have not had a hysterectomy and higher risk of developing blood clots, among other side effects. However, there are some foods that can protect against endometrial cancer and blood clots while not interfering with tamoxifen's effectiveness.

Certain selective serotonin reuptake inhibitor (SSRI) antidepressants such as Paxil and Prozac, as well as some other medications, have been found to interfere with tamoxifen treatment in some women and should be avoided. Exposure to light at night suppresses melatonin production, which in turn can lead to tamoxifen resistance. Regular aspirin use appears to enhance the effectiveness of tamoxifen.

Tamoxifen and body weight

There is some evidence that overweight women have a more favorable prognosis than normal weight women after tamoxifen treatment. However, weight gain, which is common during tamoxifen treatment, has been found to be associated with less favorable prognosis. Please see our article on the latest research concerning the impact of endocrine treatment on breast cancer prognosis.

Tamoxifen and cholesterol

Breast cancer typically eventually develops resistance to tamoxifen. There is some evidence that breast cancer cells that don't respond to tamoxifen may be using cholesterol to shield themselves against the drug. While it is not clear that reducing dietary cholesterol would greatly affect this process, it may make sense for breast cancer patients on tamoxifen to reduce their cholesterol to low-normal levels.

Tamoxifen might increase risk of type 2 diabetes

It has been reported that tamoxifen use in breast cancer survivors is associated with an increased risk of type 2 diabetes. This risk may be higher in women who have other risk factors for diabetes.

Vitamin D and other micronutrients influence tamoxifen treatment

Vitamin D has been shown to inhibit the growth of tamoxifen-resistant breast cancer cells in the laboratory and resveratrol has been found to reduce their proliferation. Selenium and conjugated linoleic acid (CLA) may enhance the effectiveness of tamoxifen, whereas vitamin C, red clover and tangeretin have been shown to reduce it. In addition, brassica vegetables contain sulforaphane, an histone deacetylase (HDAC) inhibitor that may cause a synergistic increase in apoptosis and cell death in combination with tamoxifen

Foods that enhance the effectiveness of tamoxifen treatment

The following foods (or major components) have been found to increase the anti-breast cancer effects of tamoxifen treatment:

Arugula
Black pepper
Blackberries
Blueberries
Brazil nuts
Broccoli
Brussels sprouts
Buckwheat
Cabbage
Cauliflower
Celery
Cherries, especially sour or tart
Coffee
Collard greens
Cranberries
Flaxseed
Grapes, red
Green tea
Herring
Kale
Kefir
Lake trout
Mackerel
Mushrooms
Mustard
Mustard greens
Parsley
Pomegranates
Salmon, wild
Sardines
Seaweed
Tomatoes
Walnuts
Watercress
Wheat germ
Yogurt, lowfat

Brazil nut consumption should be limited to no more than one nut per day, on average, to avoid consuming excess selenium.

Foods and supplements that should not be used during tamoxifen treatment

The following foods (or major components) and supplements have been found to reduce the effectiveness of tamoxifen and should be avoided during tamoxifen treatment:

Alcohol
Daidzein
DIM (3,3'-diindolylmethane)
Orange or tangerine peel - found in orange tea, orange marmalade, Szechuan Orange Chicken
Corn oil
Curcumin supplements
Genistein
Hormone replacement therapy (HRT), including bioidentical or natural hormones
L-carnitine
Red clover supplements
Sesame seeds
Si-Wu-Tang - a Chinese medicine herbal preparation
Soybean paste
Soy protein isolate
Soybeans
Tangeretin supplements
Tofu
Vitamin E supplements
Preliminary evidence suggests that exposure to bisphenol A (BPA) or parabens could interfere with the effectiveness of tamoxifen treatment.

Foods that reduce the risk of endometrial cancer

The following foods (or major components) have been associated with lower risk of endometrial cancer while also protecting against breast cancer:

Arugula
Bell peppers
Black pepper
Black tea
Brazil nuts
Broccoli
Brussels sprouts
Carrots
Cherries, sour
Collard greens
Garlic
Green tea
Herring
Honey, minimally processed*
Hot peppers
Kale
Lake trout
Leeks
Lettuce, romaine
Mackerel
Mustard greens
Onions
Pomegranates
Pumpkins
Saffron
Salmon, wild
Sardines
Seaweed
Tomatoes
Spinach
Turmeric
Turnip greens
Walnuts
Watercress
Watermelon
Zucchini

'*In moderation.

Foods that increase the risk of endometrial cancer

The foods and supplements listed below have been associated with increased risk of endometrial cancer. Sweets and other foods with high glycemic index, as well as animal fats, have been shown to increase the risk. Exposure to cadmium is associated with increased risk. Foods with high acrylamide content, such as French fries, cereal, potato chips, potatoes, and baked goods, have also been shown to increase risk of endometrial cancer.

Bacon
Beef
Bread, baguettes & croissants
Butter
Cheese, full fat
Cookies, candy and cake
Fried ripe plantains
Genistein & daidzein
Granola
Milk, whole
Potatoes, potato chips & French fries
Shellfish
Sugar
Sweet desserts
Sweetened breakfast cereals
Well done or fried meat
White rice
Long-term electric blanket use has also been found to be associated with increased risk of endometrial cancer and should be avoided.

Foods that reduce the risk of blood clots

The foods below have been reported to decrease the likelihood of blood clots while protecting against or being neutral with respect to breast cancer risk.

Garlic
Herring
Honey, minimally processed
Lake trout
Mackerel
Saffron
Salmon, wild
Sardines
Strawberries
Turmeric
Walnuts

Foods that reduce cholesterol

The following foods have been shown to improve cholesterol profile while at the same time protecting against breast cancer:

Apples
Bell peppers
Blueberries
Broccoli
Brown rice
Brussels sprouts
Buckwheat
Cabbage
Canola oil
Carrots
Celery
Cherries
Cranberries
Cucumbers
Dry beans
Fatty fish
Flaxseed
Grapes
Greens
Horseradish
Hot peppers
Kale
Lettuce
Mushrooms
Olive oil
Pomegranates
Seaweed
Spinach
Walnuts

Foods that increase cholesterol

The following foods have been shown to worsen cholesterol profile:

Bacon
Beef
Butter
Caviar
Cheese
Coffee
Milk, whole or cream
Partially-hydrogenated oil
Pork

Additional comments

Tamoxifen is a selective estrogen receptor modulator (SERM), down-regulating ERα but not ERβ (in contrast, aromatase inhibitors such as Arimidex up-regulate ERβ). Tamoxifen is effective in preventing ER+ breast cancer and in treating early stages, but this effectiveness may be lost over time if the cancer progresses despite treatment. Also, tamoxifen does not prevent ER- breast cancer. Women who develop primary breast cancer or a recurrence despite tamoxifen treatment are at increased risk of developing ER- breast cancer, a more aggressive disease than ER+. Therefore, it is important for women being treated with tamoxifen to eat a wide variety of the foods from our recommended and limit or avoid those on our avoid list, in addition to paying particular attention to the foods listed above.

Below are links to recent studies on this topic. For a more complete list of studies, please click on tamoxifen.