A number of hereditary and lifestyle factors-including genetic mutations, a family history of the disease and alcohol consumption-are already known to raise breast-cancer risk, but whether environmental pollutants have a role to play has been controversial.
Over the past year, however, the evidence has been stacking up to show that chemicals in the air we breathe and food we eat could be contributing to breast cancer, and may be behind the rising rates of the disease over the past few decades.
One recent ground-breaking study carried out by a team of researchers from McGill University and the University of Montreal
in Quebec, Canada, found a disturbing link between breast cancer and traffic-related air pollution.
They combined the data from several earlier studies to create two air pollution 'maps' showing levels of nitrogen dioxide (NO2), a byproduct of vehicular traffic, in different parts of Montreal in 1996 and 10 years earlier in 1986. They then crossed-linked these data with the addresses of nearly 800 postmenopausal women with and without breast cancer.
The results showed that women living in areas with higher levels of NO2-a marker of traffic-related air pollution-had a higher risk of breast cancer. Specifically, the risk increased by about 25 per cent with every NO2 increase of 5 ppb (parts per billion) of exposure.
According to study co-author Dr Mark Goldberg, "[A]nother way of saying this is that women living in the areas with the highest levels of pollution were almost twice as likely to develop breast cancer as those living in the least polluted areas" (Environ Health Perspect, 2010; 118: 1578-83).
Although the findings aren't proof that exposure to traffic pollution causes breast cancer, the idea is certainly plausible, given that several pollutants produced by cars and other vehicles, such as benzene and polycyclic aromatic hydrocarbons (PAHs), are known carcinogens.
Moreover, previous studies have also found a link between air pollution and breast cancer. One-the Western New York Exposures and Breast Cancer (WEB) study-reported that early life exposures to relatively high concentrations of traffic emissions were associated with a signifi-cantly increased risk of postmeno-pausal breast cancer in non-smokers (Cancer Causes Control, 2007; 18: 947-55).
Clearly, more research is needed, but it may be that breast cancer is yet another health problem caused by polluted air-along with heart disease and lung cancer (see WDDTY, vol 18 no 5).
The chemicals we clean our homes with might also be related to breast cancer, according to a recent study. Researchers from the Silent Spring Institute in the US quizzed more than 1500 women about their cleaning-product use, and found that those who reported using more air fresheners and products for mould and mildew control had a higher incidence of breast cancer.
The study involved 787 women living in Cape Cod, MA, and 721 controls. In telephone interviews, the women were asked about their use of cleaning products, beliefs about breast cancer causes, and established and suspected risk factors.
Overall, the women who reported the highest combined cleaning-product use had twice the risk of breast cancer compared with those with the lowest reported use.
The researchers concluded that exposure to household cleaning products may well increase the risk for breast cancer. However, they cautioned that their findings may not be entirely accurate, given that women with breast cancer who believed that chemi-cals and pollutants contribute "a lot" to the risk of developing the condition were more likely to report high product use.
Nevertheless, the researchers also highlighted the fact that exposure to chemicals from household cleaning products is a "biologically plausible cause of breast cancer". Indeed, numerous products contain ingredients that are "mammary-gland carcinogens in animals or endocrine-disrupting compounds (EDCs), including compounds that affect the growth of oestrogen-sensitive human breast cancer cells or affect mammary gland development", the study said (Environ Health, 2010; 9: 40).
One group of chemicals to watch out for in your cleaning products is phthalates, the plastics chemicals that are also commonly found in adhesives, flooring, food-packaging and cosmetics. These compounds are known to be endocrine disruptors, and we are widely exposed to them via ingestion (they can migrate from wrappers and containers into foods and drinks), inhalation (they are commonly found in household dust) and skin absorption.
In recent years, phthalates have been linked to a host of health problems, ranging from asthma and allergies to infertility and hormonal changes (Altern Med Rev, 2010; 15: 190-6). Now, a first-of-its-kind study has found that exposure to these chemicals might also increase the risk of breast cancer.
A team of researchers led by Lizbeth L'opez-Carrillo at Mexico's National Institute of Public Health analyzed urine samples from 454 Mexican women-233 with breast cancer and 221 controls-and found phthalate metabolites in at least 82 per cent of the women.
More alarming, monoethyl phthalate (MEP), which is a metabolite of diethyl phthalate (DEP), was found in higher concentrations in the cancer cases than in the controls, suggesting that exposure to DEP can boost the risk of breast cancer.
Women with the highest levels of MEP in their urine were more than twice as likely to have breast cancer compared with women with the lowest levels. In the case of postmenopausal women, the odds were even higher: they were more than four times as likely to have the disease. What's more, the MEP levels found in these women weren't abnormally high, but were levels similar to those found in most US residents (Environ Health Perspect, 2010; 118: 539-44).
These studies are shocking, but they suggest that, in addition to following a healthy diet and taking regular exercise, minimizing our exposure to toxic chemicals may help to prevent breast cancer. Although it's impossible to live a completely chemical-free life, there are a number of steps you can take to reduce your exposure to those agents that may be putting you at risk (see box, page 19).
Factfile: Other chemicals to watch out for
u Pesticides. Residential pesticide use was linked to breast cancer in a US study (Am J Epidemiol, 2007; 165: 643-51).
u Bisphenol A. Commonly found in canned food, BPA is a known endocrine disruptor and could potentially play a role in breast cancer (Arch Toxicol, 2009; 83: 281-5).
u Cigarette chemicals. Even passive smoking can boost breast cancer risk, according to a recent US study (BMJ, 2011; 342: d1016).
u Synthetic musks. Certain synthetic musk fragrances, commonly used in perfumes, significantly increased the growth of human breast-cancer cells in test-tube studies (Arch Environ Contam Toxicol, 2002; 43: 257-64).
Factfile: Cutting out the chemicals
u Air pollution. Keep tabs on the air pollution in your area by contacting your local
air-quality monitoring service (in the UK: www.airquality.co.uk/index.php; in the US: www.epa.gov/ oar/airpolldata.html). When pollution levels are high:
v stay indoors as much as you can, where the levels of many pollutants are usually lower than outdoors;
v if you must go outside, limit outdoor activities to before noon or wait until after sunset, especially when smog levels are high;
v stay away from high traffic areas and avoid outdoor activities near these areas at all times;
v don't exercise or exert yourself outdoors when air-quality reports indicate unhealthy conditions, as the faster you breathe, the more pollution you draw into your lungs; and
v do your bit by avoiding using the car as much as you can. If you have to drive, make sure your car is as 'green' as possible by keeping it regularly tuned-a petrol-efficient car can considerably reduce noxious emissions. Also, keep your speed down. A slower car burns less fuel and, thus, produces less exhaust. For more information on how to become a greener motorist, visit the Environmental Transport Association's website at www.eta.co.uk, or see www.greenercars.com.
u Cleaning chemicals. Be aware that most cleaning products on the market contain a cocktail of potentially harmful chemicals. Choose alternative brands such as Ecover, Bio-D and Method, or try making your own natural cleaning solutions. For example, a simple solution of one part vinegar to one part water makes an excellent all-purpose cleaner.
u Phthalates. According to Pollution in People, a report by the Toxic-Free Legacy Coalition in the US (see www.pollutioninpeople.org), you can reduce exposure to phthalates by using the following.
v PVC (polyvinyl chloride)-free building products. Avoid vinyl windows and doors, and choose wood instead. For flooring, choose linoleum, cork, bamboo or wood rather than vinyl. Adhesives, caulk, grout and sealants may also contain phthalates, so always check
the ingredients before purchasing.
v PVC-free shower curtains. Avoid vinyl shower curtains in favour of natural fibres, polyester or nylon.
v PVC-free packaging. Examine the recycling symbol on products you purchase wrapped in plastic packaging, as plastics marked with the number '3' in the symbol contain PVC.
v PVC-free food storage. Buy plastic wrap and storage bags made from polyethylene rather than PVC. For storing food, use glass containers, or plastic containers that are marked with recycling symbols and numbers other than '3' and '7' (to avoid BPA, too).
v phthalate-free cosmetics. Check ingredients lists and avoid products that include 'fragrance' or phthalates. Choose products from companies such as Dr Hauschka, Lavera and Green People, which make a point of using natural ingredients.
WDDTY VOL. 22 NO. 2