Exposure to certain banned pesticides increases breast cancer risk. Some of these persist in the environment.
Pesticides which are currently used, e.g. glyphosate (a weed killer) and malathion (used to kill insects), may also increase breast cancer risk, although more studies are needed to confirm this.
Certain pesticides are carcinogens or endocrine disrupting chemicals that interfere with oestrogen. Early life exposure may affect breast development, increasing susceptibility to breast cancer later in life.
Eating organic food will reduce pesticide exposure.
What are pesticides?
Pesticides are chemical compounds that are used to kill pests, including insects, rodents, fungi and weeds (1). They are used in public health to kill vectors of disease, such as mosquitoes, and in agriculture to kill pests that damage crops. The two most commonly used pesticides are herbicides used to kill weeds; and insecticides used against insects.
Many pesticides are toxic and potentially harmful to animals, plants and humans (2). Some have the potential to disrupt our hormone systems and can play a role in development of cancers, such as non-Hodgkin lymphoma, colorectal and breast cancers (3).
Why are we concerned about pesticides?
Pesticides could increase our risk of breast cancer in several ways. Some can act as breast carcinogens (cancer-causing agents) by causing gene mutations that lead to, or promote, growth of cancer (6), or they may act as endocrine disrupting chemicals (EDCs) and disrupt sex hormones such as oestrogen – high levels of which can increase breast cancer risk (7). Exposure to pesticides in the womb (in utero) may make us more vulnerable to developing breast cancer as adults (8).
Is there a link between pesticides and breast cancer?
Several pesticides are banned as they are known to harm human health or the environment (9). Some of these have links to breast cancer. For example, the insecticide DDT was banned in 1986, due to several health concerns, including an increased risk of breast cancer. Other banned pesticides that are EDCs and/or cause mammary tumours in animals include lindane, chlorpyrifos and parathion, which were all once used to control insects.
Many pesticides used today are EDCs that affect oestrogen or cause mammary cancer in animals. Commonly used examples are the insecticide deltamethrin and the herbicide glyphosate, (commonly known as “Round-up”) which cause mammary tumours in rodents (10, 11), and interfere with oestrogen (12). In 2015 glyphosate and the insecticide malathion were classified as probable human carcinogens (13). They may also increase breast cancer risk (14–16), but more studies are needed to confirm this (11, 15, 16).
Human studies have linked pesticides with breast cancer.
Human population studies suggest past exposure to specific pesticides including dieldrin (17), DDT (18) and chlorpyrifos (19) (no longer in use) and captan (17) (still in use) increase breast cancer risk. To date, no studies have shown recent exposure to glyphosate increases breast cancer incidence (13),(15). Most studies examining general pesticide exposure with breast cancer incidence show an elevated breast cancer risk (20–24). To better understand the effects of pesticide exposure on breast cancer risk more long-term human studies involving individual and total pesticide exposures are needed.
Does organic food help reduce breast cancer risk?
Chemical pesticides for use against weeds, plant diseases and pests are banned in all organic food production in the UK (see here) While organic food contains less pesticide residue than conventionally farmed foods (25), it is unclear whether eating organic food reduces breast cancer risk (26). This is because there haven’t been enough studies in this area. However, given the likelihood that long-term pesticide exposure may increase breast cancer risk we recommend eating organic food or food produced with little or no pesticide, where possible.
For more information on pesticides, organic food and breast cancer, see our science briefing.
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