Breast Cancer

References & Evidence Notes

Each numbered entry below is either a source you can follow or a note setting out what the evidence does and does not support. Both are numbered together so the markers in the text line up.

Last reviewed October 20, 2026. Supplement entries are cross-checked against the NIH National Center for Complementary and Integrative Health and the Linus Pauling Institute Micronutrient Information Center.⁴² Nothing on this page treats breast cancer. Surgery, radiation therapy, endocrine therapy, chemotherapy and targeted agents treat breast cancer, and they have transformed survival from it. What nutrition and lifestyle can genuinely do is support you through treatment, help manage its side effects, maintain strength and weight, and contribute to long-term health afterwards. Be careful with supplements specifically: several interact with treatment, high-dose antioxidants during chemotherapy and radiation therapy may reduce their effectiveness, and some phytoestrogen supplements interact with tamoxifen. Share your full supplement list with your oncology team and let them make the call. Be skeptical of anything promising to starve, reverse or cure cancer through diet; that claim has been made for a century and has never survived a trial. Diet and supplements are not an alternative to surgery, chemotherapy, radiation therapy or immunotherapy, and no dietary change should delay or replace treatment decided with your oncology team.

1. On US statistics: SEER projects 321,910 new cases of female breast cancer in the US in 2026 and estimates lifetime risk at about 13.0% (2021 to 2023 data). Five-year relative survival was 91.9% for all stages combined (2016 to 2022): 100.0% when the cancer was confined to the breast (64% of cases), 87.5% after spread to regional lymph nodes (27%) and 33.8% after spread to distant organs (6%). Hormone-receptor-positive, HER2-⁠negative cancer is the most common subtype, about 70% of cases, SEER, female breast cancer, SEER, breast cancer subtypes. ↩
2. On alcohol: alcohol is classified by IARC as a Group 1 carcinogen, a category that describes how strong the evidence is that it causes cancer, not how large the risk is, and it is associated with increased breast cancer risk in a dose-dependent way, with no clearly safe threshold identified: a reanalysis of individual data from 53 studies, covering 58,515 women with breast cancer, found risk rose by 7.1% for every extra 10 g of alcohol per day, which is about one drink, PubMed 12439712. This is one of the few genuinely modifiable dietary risk factors for the disease, and it is more useful than most of what gets discussed. ↩
3. On the global picture: the World Health Organization reports that in 2024 about 2.4 million women were diagnosed with breast cancer and 694,000 died of it, that it was the most common cancer in women in 164 of 186 countries, and that about 80% of breast cancers occur in women with no specific risk factor other than sex and age, WHO, breast cancer fact sheet. ↩
4. On inherited risk: National Cancer Institute guidance states that pathogenic variants in the highly penetrant breast and ovarian cancer genes, such as BRCA1 and BRCA2, are rare in the general population and account for no more than 5% to 10% of breast and ovarian cancer cases overall, NCI PDQ, genetics of breast and gynecologic cancers. ↩
5. On screening: mammographic screening reduces breast cancer mortality. An independent UK panel pooling 11 randomized trials put the relative risk of breast cancer death for women invited to screening at 0.80, a reduction of 20%, PubMed 23117178. The size of the benefit and the age at which to start are debated between guideline bodies, and overdiagnosis, meaning cancers found at screening that would never have surfaced in a woman's lifetime, is a genuine and acknowledged harm that the same panel set out to quantify. The debate is about how much benefit and at what cost, not about whether screening works. Any new breast lump, skin or nipple change, or bloody nipple discharge should be assessed regardless of when you were last screened. ↩
6. On modifiable risk: in the Nurses' Health Study, with 8,421 invasive breast cancers among 121,700 postmenopausal women followed from 1980 to 2010, weight gain, alcohol, low physical activity, not breastfeeding and menopausal hormone therapy together accounted for 34.6% of cases. The share was higher for estrogen receptor-positive disease (39.7%) than receptor-negative disease (27.9%), PubMed 27923781. ↩
7. On bone health: aromatase inhibitors accelerate bone loss, and treatment-induced menopause does the same. Calcium and vitamin D adequacy, resistance exercise and bone density monitoring are part of standard survivorship care. This is an area where nutrition is doing real, specific work. ↩
8. On risk factors: NHS guidance lists being over 50, dense breast tissue, a family history of breast or ovarian cancer, certain breast conditions including ductal and lobular carcinoma in situ, periods starting before 12, menopause after 55, having no children or a first child after 30, not breastfeeding, and using birth control pills or menopausal hormone therapy, which it says only slightly increase risk, with benefits that outweigh the risks for many people. It advises genetic assessment when breast or ovarian cancer runs in the family, and names medicines and risk-reducing surgery as options for people at very high risk, NHS, causes of breast cancer in women. ↩
9. On symptoms to get checked: NHS guidance advises seeing a doctor for a lump or swelling in the breast, chest or armpit, or any change in the breasts or nipples that is not normal for you, and not waiting for the next screening appointment even if you have recently been screened, NHS, symptoms of breast cancer in women. ↩
10. On BRCA1 and BRCA2: the National Cancer Institute states that more than 60% of women who inherit a harmful change in BRCA1 or BRCA2 will develop breast cancer during their lifetime, against about 13% of women in the general population, NCI, BRCA gene changes. ↩
11. On what Group 1 means: the World Health Organization explains that IARC classifications describe the strength of the evidence that something causes cancer, not the level of risk, so agents in the same group are not equally dangerous, WHO, carcinogenicity questions and answers. ↩
12. On alcohol and weight: the World Cancer Research Fund states that drinking any amount of alcohol increases breast cancer risk before and after menopause, and the less you drink the lower the risk, and that gaining weight as an adult and living with overweight or obesity increase the risk of breast cancer after menopause. It finds no consistent evidence that soy foods increase breast cancer risk, World Cancer Research Fund, breast cancer causes. ↩
13. On weight gain after menopause: in the Nurses' Health Study, 49,514 postmenopausal women were followed for up to 24 years; those who gained 10 kg or more since menopause had an 18% higher risk of breast cancer than those whose weight stayed stable, and women who lost 10 kg or more after menopause and kept it off, and had never used hormone therapy, had a lower risk, PubMed 16835425. ↩
14. On screening in the US: the US Preventive Services Task Force recommends a screening mammogram every 2 years for women aged 40 to 74, and finds the evidence insufficient to judge screening from 75 or extra ultrasound or MRI screening for dense breasts after a normal mammogram, USPSTF, breast cancer screening. ↩
15. On screening in the UK: the NHS invites women registered as female with a doctor's practice for breast screening from age 50, with the first invitation between 50 and 53 and then every 3 years until their 71st birthday; from 71 they can still ask for screening every 3 years, NHS, who breast screening is for. ↩
16. On diet and recurrence, including the trial that did not work. Two large randomized dietary trials were run in breast cancer survivors and they did not agree. WHEL (Women's Healthy Eating and Living, JAMA 2007) randomized 3,088 survivors to a diet very high in vegetables, fruit and fiber and lower in fat, and found no reduction in breast cancer events or mortality over a mean 7.3 years of follow-up, PubMed 17635889. WINS (Women's Intervention Nutrition Study, JNCI 2006) randomized 2,437 survivors to dietary fat reduction and found a modest reduction in relapse, 9.8% against 12.4%, a hazard ratio of 0.76 with a confidence interval of 0.60 to 0.98, PubMed 17179478. Exploratory analyses suggested the effect differed by hormone receptor status, and the intervention group also ended 6 lb (2.7 kg) lighter, so weight loss is a plausible contributor rather than fat reduction alone. Citing WHEL as evidence that diet reduces recurrence inverts its actual result. What does have consistent evidence is physical activity and avoiding weight gain, both associated with better outcomes in observational cohorts. ↩ ↩
17. On mind-body care during treatment: the Society for Integrative Oncology guideline on breast cancer, later endorsed by ASCO, recommends meditation, yoga, stress management and music therapy for anxiety, several of these for mood, meditation and yoga for quality of life, and acupuncture or acupressure for chemotherapy nausea. It advises against acetyl-L-carnitine for nerve damage because of possible harm, and finds no strong evidence for any ingested dietary supplement to manage treatment side effects, PubMed 28436999. ↩
18. On soy, which worries people unnecessarily. Concern arose because isoflavones bind estrogen receptors and because of rodent studies. Human evidence points the other way: observational cohorts including the Shanghai Breast Cancer Survival Study, and pooled analyses of US and Chinese cohorts, associate higher whole-soy intake in survivors with no increase in recurrence and in some analyses a modest reduction, including among women taking tamoxifen. Major cancer organizations regard whole soy foods as safe for survivors. This is observational evidence, so the honest conclusion is that soy foods are safe to eat, not that they are treatment. Concentrated isoflavone supplements are a different matter and are not the same as eating tofu. ↩ ↩
19. On flaxseed: in a randomized, placebo-controlled trial of 32 postmenopausal women with newly diagnosed breast cancer, a daily muffin containing 25 g of flaxseed, eaten for about five weeks before surgery, lowered a marker of tumor cell growth (Ki-⁠67) against a control muffin. The trial measured tumor markers, not recurrence or survival, PubMed 15897583. ↩
20. On vitamin D and cancer: in the VITAL trial, 25,871 adults randomly assigned to 2,000 IU of vitamin D a day or placebo for a median of 5.3 years had no lower rate of invasive cancer, and the hazard ratio for breast cancer was 1.02, no different from placebo, PubMed 30415629. ↩
21. On omega-⁠3 for joint pain from aromatase inhibitors: in a randomized, placebo-controlled trial of 249 women, 3.3 g of omega-⁠3 a day for 24 weeks gave no more relief than placebo; joint pain improved substantially in both groups, PubMed 25940724. ↩
22. On supplement interactions during treatment: high-dose antioxidant supplementation during chemotherapy or radiation therapy is generally advised against, on the reasoning that these treatments work partly through oxidative damage. In a study run alongside a breast cancer chemotherapy trial, women taking antioxidant supplements both before and during treatment had a higher hazard of recurrence, 1.41 with a confidence interval of 0.98 to 2.04, which did not reach statistical significance, PubMed 31855498. A 2024 review of 24 systematic reviews found the wider evidence mixed rather than settled, PubMed 39078314. St. John's wort induces cytochrome P450 enzymes and reduces levels of several anticancer drugs, with clinically significant interactions documented for imatinib and irinotecan, PubMed 23394826. Grapefruit inhibits CYP3A4 through furanocoumarins, chiefly bergamottin, which is why it is listed against so many medicines, PubMed 37307228. This is why the supplement list belongs with the oncology team rather than in a drawer. ↩
23. On treatment and outcome: breast cancer is not one disease. Treatment is determined by subtype, defined by estrogen and progesterone receptor status, HER2 status and stage. Five-year survival for localized disease is high in countries with screening and modern treatment, and the gains come from early detection and systemic therapy. ↩
24. On endocrine therapy: the NCI hormone therapy fact sheet explains that aromatase inhibitors are used mainly after menopause, and before menopause only together with a drug that suppresses ovarian function. It also says that hormone therapy taken for 5 years or more greatly reduces the risk of recurrence, of new breast cancer and of dying from breast cancer, NCI, 2025. ↩
25. On extended endocrine therapy: the 2019 ASCO focused update, based on six trials, recommends extended therapy including an aromatase inhibitor for up to a total of 10 years in node-positive disease, and suggests many women with node-negative disease consider it. It notes that the absolute benefits are modest and that bone-related side effects are more common, PubMed 30452337. ↩
26. On newer agents: the NCI list of drugs approved for breast cancer includes the CDK4/6 inhibitors palbociclib and ribociclib, the antibody-drug conjugates trastuzumab deruxtecan and sacituzumab govitecan, and the immunotherapy drug pembrolizumab, NCI, 2026. ↩
27. On the 21-⁠gene recurrence score: a trial in 10,273 women with hormone-receptor-positive, HER2-⁠negative, node-negative breast cancer found that for a midrange score of 11 to 25, endocrine therapy alone was noninferior to adding chemotherapy, with some benefit of chemotherapy in women 50 years of age or younger with a score of 16 to 25, PubMed 29860917. ↩
28. On DIM and tamoxifen: in a randomized, placebo-controlled trial, 130 women taking tamoxifen were given 150 mg of DIM twice a day or placebo for 12 months; DIM changed urine estrogen metabolites but not breast density, and it lowered blood levels of the active tamoxifen metabolites, including endoxifen. The authors called for research on whether that weakens tamoxifen's benefit, PubMed 28560655. ↩
29. On soy supplements with hormone therapy: the integrative medicine service at Memorial Sloan Kettering Cancer Center advises that soy is generally safe in food, but that anyone taking tamoxifen should talk with their healthcare provider before using soy supplements, because they can affect how it works, and likewise anyone taking an aromatase inhibitor, Memorial Sloan Kettering, soy. ↩
30. On sugar and fast food: the World Cancer Research Fund advises limiting foods and drinks with added sugars and "fast foods" high in fat, starches or sugars, because eating them often can lead to weight gain, and states there is strong evidence that regularly drinking sugar-sweetened drinks leads to weight gain; it lists weight gain in adulthood as a risk factor for breast cancer after menopause, World Cancer Research Fund, sugar and cancer. ↩
31. Kroenke CH, Kwan ML, Sweeney C, Castillo A, Caan BJ. High- and low-fat dairy intake, recurrence, and mortality after breast cancer diagnosis. J Natl Cancer Inst. 2013;105(9):616-⁠623. PubMed 23492346. In 1,893 women with early-stage breast cancer followed for a median 11.8 years, 1 or more servings of high-fat dairy a day was linked with higher breast cancer mortality (hazard ratio 1.49), while low-fat dairy was unrelated to recurrence or survival; this is an observational association. ↩
32. Fiolet T, Srour B, Sellem L, Kesse-Guyot E, Allès B, Méjean C, Deschasaux M, Fassier P, Latino-Martel P, Beslay M, Hercberg S, Lavalette C, Monteiro CA, Julia C, Touvier M. Consumption of ultra-processed foods and cancer risk: results from NutriNet-Santé prospective cohort. BMJ. 2018;360:k322. PubMed 29444771. In 104,980 French adults, each 10% increase in the share of ultra-processed foods in the diet was linked with a 12% higher risk of cancer overall and an 11% higher risk of breast cancer (hazard ratios 1.12 and 1.11); this is an observational association. ↩
33. Gencer B, Djousse L, Al-Ramady OT, Cook NR, Manson JE, Albert CM. Effect of long-term marine omega-⁠3 fatty acids supplementation on the risk of atrial fibrillation in randomized controlled trials of cardiovascular outcomes: a systematic review and meta-analysis. Circulation. 2021;144(25):1981-⁠1990. PubMed 34612056. Seven trials with 81,210 people followed for about 5 years: omega-⁠3 supplements were linked to a higher risk of atrial fibrillation (hazard ratio 1.25), more so in trials of more than 1 g a day (1.49), and the risk rose with each additional gram. ↩
34. On melatonin: in a randomized, placebo-controlled trial of 95 postmenopausal breast cancer survivors, 3 mg of melatonin a night for 4 months improved self-reported sleep quality, with no difference in depression or hot flashes, PubMed 24718775. ↩
35. On melatonin in pregnancy: the NIH National Center for Complementary and Integrative Health notes that there has been a lack of research on the safety of melatonin in pregnant or breastfeeding women, NCCIH, melatonin. ↩
36. On curcumin: in a randomized, placebo-controlled trial of 686 women having breast radiation therapy, 6 g of curcumin a day did not reduce radiation skin damage, PubMed 29192329. In women taking tamoxifen, curcumin lowered blood levels of tamoxifen and its active metabolite endoxifen, and the authors warn this could push endoxifen below the level needed for it to work, PubMed 30909366. ↩
37. On turmeric in pregnancy: the NIH National Center for Complementary and Integrative Health states that turmeric supplements may be unsafe during pregnancy, and that little is known about amounts above those in food while breastfeeding, NCCIH, turmeric. ↩
38. On medicinal mushroom extracts after breast cancer: in a dose-escalation trial in 34 women after breast cancer treatment, a maitake extract raised some immune measures and lowered others, and the authors warn that such extracts may depress as well as enhance immune function, PubMed 19253021. ↩
39. On preventing nerve damage from chemotherapy: the 2020 ASCO guideline update reconfirmed that no agent is recommended to prevent chemotherapy-induced peripheral neuropathy, and discourages acetyl-L-carnitine, PubMed 32663120. ↩
40. On exercise during treatment: an ASCO guideline based on 52 systematic reviews and 23 further randomized trials found that exercise during cancer treatment improved fitness, strength and fatigue, and recommends regular aerobic and resistance exercise during treatment given with curative intent; it found the evidence for other diet and weight-loss interventions during treatment very limited, PubMed 35576506. ↩
41. On fever during treatment: the National Cancer Institute states that infections during cancer treatment can be life-threatening and need urgent medical attention, that treatments such as chemotherapy raise the risk, and lists a fever of 100.5°F (38°C) or higher among the signs, NCI, infection and neutropenia. ↩
42. National Center for Complementary and Integrative Health (NIH), nccih.nih.gov, and the Linus Pauling Institute Micronutrient Information Center, lpi.oregonstate.edu/mic. ↩
43. On the Mediterranean diet: in a secondary analysis of the PREDIMED trial (Toledo and colleagues, JAMA Internal Medicine, 2015), 4,152 women aged 60 to 80 at high cardiovascular risk were followed for a median of 4.8 years; with only 35 breast cancers in total, women given a Mediterranean diet with extra-virgin olive oil had fewer breast cancers than those advised to cut fat, and the authors state that the result rests on few cases and needs confirming in larger, longer studies, PubMed 26365989. ↩