How diet, nutrition and physical activity affect breast cancer risk. In total, we analysed 119 studies from around the world, comprising more than 12 million women and over 260,000 cases of breast cancer.
Breast tissue comprises mainly fat, glandular tissue (arranged in lobes), ducts and connective tissue. Breast tissue develops in response to hormones such as oestrogens, progesterone, insulin and growth factors. The main periods of development are during puberty, pregnancy and lactation. The glandular tissue atrophies after menopause. Breast cancers are almost all carcinomas of the epithelial cells lining the breast ducts (the channels in the breast that carry milk to the nipple). Although breast cancer can occur in men, it is rare (less than 1 per cent of cases) and is not included in this review.
Our Expert Panel has reviewed the evidence on diet, weight, physical activity and the risk of breast cancer.
There is strong evidence that:
There is some evidence that:
There is strong evidence that:
There is limited evidence that:
In addition to the findings on diet, nutrition and physical activity outlined above, other established causes of breast cancer include:
Early menarche (before the age of 12), late natural menopause (after the age of 55), not bearing children and first pregnancy over the age of 30 all increase lifetime exposure to oestrogen and progesterone and the risk of breast cancer. The reverse also applies: late menarche, early menopause, bearing children and pregnancy before the age of 30 all reduce the risk of breast cancer.
Ionising radiation exposure from medical treatment such as X-rays, particularly during puberty, increases the risk of breast cancer, even at low doses.
Hormone therapy, also known as hormone replacement therapy or HRT, (containing oestrogen with or without progesterone) increases the risk of breast cancer, and the risk is greater with combined oestrogen plus progesterone preparations. Oral contraceptives containing both oestrogen and progesterone also cause a small increased risk of breast cancer in young women, among current and recent users only.
Breast tissue varies at different stages of life in response to host hormonal status and other environmental influences. It is therefore possible that some risk factors will have different effects at different life stages.
Hormones play an important role in breast cancer progression because they modulate the structure and growth of epithelial tumour cells. Different cancers vary in hormone sensitivity. Breast cancers can be classified by their hormone receptor type; for example, to what extent the cancer cells have receptors for the hormones oestrogen and progesterone, which can affect the growth of the breast cancer cells.
Breast cancer cells that have oestrogen receptors are referred to as oestrogen-positive (ER+), while those containing progesterone receptors are called progesterone-positive (PR+) cancers. Hormone-receptor-positive cancers are the most common subtypes of breast cancer, but vary by population (60–90 per cent). They have a relatively better prognosis than hormone-receptor-negative cancers, which are likely to be of higher pathological grade and can be more difficult to treat. Many breast cancers also produce hormones, such as growth factors, that act locally, and these can both stimulate and inhibit the tumour’s growth.
Family history of breast cancer is associated with a higher risk of the disease: women with one first-degree relative with breast cancer have almost twice the risk of women without a family history; and women with more than one first-degree relative have about a three- to four-fold higher risk. Some inherited mutations, particularly in BRCA1, BRCA2 and p53, result in a very high risk of breast cancer. Germline mutations in these genes are infrequent and account for only 2 to 5 per cent of cases. During the carcinogenic process, mutations and epigenetic modifications in oncogenes and tumour suppressor genes may be acquired by cancer cells.
Full references and a summary of the mechanisms underpinning all the findings can be found in the breast cancer report.
BREAST CANCER SURVIVORS
In 2018, World Cancer Research Fund International published Diet, Nutrition, Physical Activity and Cancer: a Global Perspective on behalf of AICR, WCRF and WKOF. This was the third in our series of major reports looking at the many ways in which our diets, and how active we are, affect our cancer risk. You can find out much more about breast cancer by downloading a pdf of the relevant chapter in the 2018 report. Please note, however, that this webpage may have been updated since the report was published.
Selected findings from this report have been published in peer-reviewed journals. Details of the papers and links to the abstract in PubMed are below:
Carbohydrates, glycemic index, glycemic load, and breast cancer risk: a systematic review and dose-response meta-analysis of prospective studies. Schlesinger S, Chan DSM, Vingeliene S, Vieira AR, Abar L, Polemiti E, Stevens CAT, Greenwood DC, Aune D & Norat T. Nutr Rev. 2017 Jun 1;75(6):420-441. Abstract
Dietary compared with blood concentrations of carotenoids and breast cancer risk: a systematic review and meta-analysis of prospective studies. Aune D, Chan DS, Vieira AR, Navarro Rosenblatt DA, Vieira R, Greenwood DC, & Norat T. Am J Clin Nutr. 2012; 96(2): 356-73. Abstract
Fruits, vegetables and breast cancer risk: a systematic review and meta-analysis of prospective studies. Aune D, Chan DS, Vieira AR, Rosenblatt DA, Vieira R, Greenwood DC, & Norat T. Breast Cancer Res Treat. 2012; 134(2): 479-93. Abstract
Dietary fibre and breast cancer risk: a systematic review and meta-analysis of prospective studies. Aune D, Chan DSM, Greenwood DC, Vieira AR, Rosenblatt DAN, Vieira R & Norat T. Ann Oncol. 2012; 23(6):1394-402. Abstract