Air pollution may be driving up rates of breast cancer in the US, Government research suggests.
Scientists found areas where toxic air levels are highest are also home to some of the highest rates of the disease in women.
The study – by the National Institutes of Health (NIH) – is one of the largest of its kind, tracking the health records of nearly 200,000 women for two decades. It used a national health study and estimates of historical air quality to determine if there was an association between air pollution and breast cancer.
It found every 10 micrograms per cubic meter (μg/m3) increase in levels of tiny pollution particles known as PM2.5 was associated with an eight percent increase in breast cancers.
PM2.5 form as a result of burning diesel, wood and coal and are so tiny they can enter the bloodstream when inhaled, where they travel to organs and cause damage linked to cancer and dementia.
Pictured above, heavy traffic on the Golden Gate Bridge in San Francisco. Among locations researchers analyzed, most women diagnosed with breast cancer lived in California, at 32 percent
A powerplant in Louisiana is pictured above. For the study, the team calculated estimated hazard ratios (HR) for pollution exposure and development of breast cancer. A hazard ratio can be considered an estimate of risk, such as the risk of developing a disease relative to exposure. HRs were lowest in Louisiana
The United States has deemed levels of PM2.5 between 12 μg/m3 and 15 μg/m3 as standard
Levels above 35 μg/m3 are considered unhealthy and prolonged exposure to levels above 50 μg/m3 can lead to serious health issues and early death. Nationally, average PM2.5 concentrations have been declining for years.
PM2.5 has been inconsistently associated with breast cancer incidence, however few studies have considered historic exposure, when levels of the pollutant were higher. While this study did find an association between the two, scientists stressed more research needs to be conducted on the topic on a national level.
Scientists at the National Institute of Environmental Health Sciences (NIEHS) and the National Cancer Institute (NCI), both part of the NIH, followed 196,905 women who had enrolled in the NIH-AARP Diet and Health Study between 1995 and 1996.
Most of the women in the study were over 50 years old and researchers’ analysis consisted primarily of postmenopausal women, a limitation of the study, researchers noted.
The study included women in California, Florida, Louisiana, New Jersey, North Carolina, Pennsylvania, Atlanta and Detroit.
Analyzing follow-up data through 2017, researchers identified 15,870 breast cancer cases and found that a 10 μg/m3 increase in PM2.5 from 1980 to 1984 was associated with an eight percent increase in overall breast cancer risk.
The above graph shows the case rate of breast cancer among women as a rate per 100,000 people compared to the death rate shown by the red squares. While case rates are still rising, deaths have declined. The blue and green dots are from two different databases tracking breast cancer rates over different time periods
Dr Alexandra White, lead author and head of the Environment and Cancer Epidemiology Group at NIEHS, said: ‘We observed an eight percent increase in breast cancer incidence for living in areas with higher PM2.5 exposure.
‘Although this is a relatively modest increase, these findings are significant given that air pollution is a ubiquitous exposure that impacts almost everyone.
‘These findings add to a growing body of literature suggesting that air pollution is related to breast cancer.’
Among locations analyzed in the study, researchers found most women diagnosed with breast cancer lived in California, 32 percent, and Florida, 21 percent.
Specifically, the association was found for ER+ tumors, masses that are estrogen receptor positive, which allows the tumor to use estrogen to grow. The association was not found for estrogen receptor negative tumors.
ER+ tumors grow more slowly and patients with this type of breast cancer tend to have a better short-term outlook, though the cancer can reoccur many years after treatment.
Associations were similar in the other time periods researchers looked at: 1985 to 1989 and 1990 to 1994.
PM2.5 is classified as a human carcinogen and contains nickel, sodium, silicon, ammonium, nitrate and sulfate, among others. Many of these can disrupt the endocrine system, which controls the body’s hormones.
For the study, the team calculated estimated hazard ratios (HR) for pollution exposure and development of breast cancer.
A hazard ratio can be considered an estimate of risk, such as the risk of developing a disease relative to exposure. The researchers determined that a 10 μg/m3 increase in PM2.5 was associated with breast cancer incidence with an HR of 1.08
When an HR is positive, it means there is an increased risk for the disease among people who are exposed compared with the unexposed group.
HRs were highest in North Carolina and Atlanta, meaning women exposed to PM2.5 there had a higher risk of developing breast cancer. HRs were lowest in Louisiana and California, though they were still positive.