Individual risk factors have been estimated to explain only 30% of breast cancers and do not fully explain why breast cancer rates have increased during our lifetimes. Widespread food supply and environmental exposures, among them exposure to polycyclic aromatic hydrocarbons (PAHs), appear to play a part in the increase. PAHs are chemicals formed during the incomplete burning of coal, oil and gas, garbage, food and other organic substances. For example, PAHs are found in well-done or fried meat and fish, as well as in vehicle exhaust and other forms of air pollution. PAHs are stored in and accumulate in fat, potentially resulting continual low-grade exposure to these carcinogens in nearby tissues.
Women with high levels of PAH exposure, whether from diet or as a result of environmental factors, have been found to have higher risk of breast cancer than those with low exposure. For example, one study of women living in Montreal reported that those living in areas with the highest levels of air pollution were almost twice as likely to develop breast cancer as those living in the least polluted areas. Now a new study has reported that overweight and obese women are more susceptible to the breast cancer-promoting effects of PAHs than normal weight and underweight women.
Sources of PAH exposure
PAHs such as acenaphthene, anthracene, benzo[a]pyrene, benzo[e]pyrene, benz[ghi]perylene, chrysene, coronene, cyclopenta[def]phenanthrene, phenanthrene, and pyrene are all known or suspected to increase the risk of various types of cancer. Benzo[a]pyrene is routinely used in animal studies to promote breast cancer development. Below are the most common sources of high exposure to PAHs:
- Air pollution & motor vehicle emissions
- Well done, broiled, or deep-fried meat or fish
- Cooking oil fumes
- Synthetic fireplace log smoke
Foods that counteract the harmful effects of PAHs
The following foods or their extracts have been shown to reduce the harmful influence of PAHs on cancer development in animal studies:
Latest research finds PAHs increase risk more in overweight women
The population study referenced at the beginning of this news story was designed to determine whether obesity influences the link between PAH exposure and breast cancer risk. The study included 1,006 postmenopausal women who had been diagnosed with primary invasive or noninvasive (in situ) breast cancer and 990 healthy women matched by age who acted as controls. The authors assessed the effects of body mass index (BMI) and weight change on a biomarker of DNA damage (PAH-DNA adduct), taking account multiple sources of long-term PAH exposure, including grilled/smoked meat intake, active cigarette smoking, living with a smoking spouse, use of synthetic fireplace logs, and proximity to vehicular traffic. DNA adducts form when DNA bonds to a chemical mutagen.
Increasing BMI was found to increase both PAH-associated DNA adducts and postmenopausal breast cancer risk. The likelihood of detectable (compared to non-detectable) adducts was increased among women with BMI ≥25 (overweight or obese) but not in those with BMI <25 (normal weight or underweight). The pattern of modification by BMI/weight gain was similar for most of the measures of PAH exposure studied, however, the estimates were imprecise. The authors conclude that the association between PAH-DNA adducts and breast cancer incidence may be elevated among overweight and obese women.