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Environmental Risk Factors

  • Polybrominated diphenyl ethers (PBDEs) are manufactured chemicals often used as flame-retardants. As consumer products treated with PBDEs reach the end of their life cycle, users often discard these products into solid-waste facilities, which may create a potential reservoir for human exposure to these chemicals.

    In 2016, researchers examined whether living within two kilometers of a solid-waste facility was associated with higher serum levels of three PBE-related chemicals: BDE-47, BDE-100, and BDE-153. They found that CTS participants who lived less than 2 kilometers from a solid-waste facility had higher levels of BDE-47 and BDE-100 than those who lived 10 or more kilometers away. Researchers did not find any association between where participants lived and the level of BDE-153 in their blood.
     Read more here.

  • Researchers studied the relationship between neighborhood environment (the social and human-made (“built”) physical attributes of an individual's surroundings), BMI, and mortality after breast cancer diagnosis. Using pooled data from the California Breast Cancer Consortium and the California Neighborhoods Data System, researchers found that neighborhood environment was associated with obesity and mortality after breast cancer diagnoses, but that these associations varied across racial/ethnic groups.  Read more here.
     

  • CTS participants who lived in a rural area during early childhood had a significantly reduced risk of developing papillary thyroid cancer as an adult.  Read more here.
     

  • A 2015 study found that CTS participants who had long-term, low-dose exposure to ambient cadmium compounds (chemical compounds in the environment containing cadmium, a type of metal) had an elevated risk of breast cancer, specifically hormone-responsive-negative tumors.  Read more here.
     

  • ETS (environmental tobacco smoke) exposures among California Teachers Study participants were highest among women who were born in the 1930s and never smoked. ETS levels steadily declined among participants born after the 1930s. ETS exposure from spousal smoking peaked during the 1950s. In the 1980s, the workplace replaced the household as the primary setting of exposure to ETS for CTS participants.  Read more here.
     

  • Researchers found that CTS participants from the San Francisco Bay area and the Southern Coastal areas had a higher rate of breast cancer than the rest of California. These residents were noted to have socioeconomic, urbanization, and personal risk factor variables that were associated with higher risk. However, even when these were controlled for, risk was still elevated in these two areas.  Read more here.
     

  • Research into environmental exposure is often complicated by residential mobility and the long latency periods of diseases like cancer. A 2005 study found CTS participants who reported an urban current address spent an average of 77% of their lives in urban areas, and participants who reported a rural current address spent an average of 67% of their lives in rural areas. The average duration of residence indicates that using current residence to research environmental effects may be feasible.  Read more here.
     

  • Researchers found that long-term exposure to fine particulate matter (PM) with a diameter of <or=2.5 μm was associated with increased risk of all-cause mortality as well as specific heart and lung-related mortality. PM components derived from combustion of fossil fuel (including diesel) were associated with some of the greatest risks.  Read more here.
     

  • Exposure to fine particulate matter (PM) with a diameter of <or=2.5 μm and PM with a diameter of <or=10 μm was associated with higher risk of ischemic heart disease mortality and stroke. Exposure to nitrogen oxides also found in air pollution was associated with increased all cardiovascular diseases mortality.  Read more here.
     

  • Researchers found that greater chronic exposure to fine particles (diameter of <or=2.5 μm) and ultrafine particles (diameter of <or=0.1 μm) were both associated with ischemic heart disease mortality.  Read more here
     

  • Melatonin levels, which mediate the body’s circadian rhythms, were found to decrease with old age, shorter nights, and residency in neighborhoods with low socioeconomic status.  Read more here.
     

  • Researchers examined the relationship between breast cancer incidence and concentrations of air pollutants shown to be mammary gland carcinogens (MGCs), modeled by annual average air concentrations though not other sources of inhalation. There was no relationship found between MGC concentration and increased risk of breast cancer.  Read more here.
     

  • Polybrominated diphenyl ethers (PBDEs) have been banned in the United States since 2005. A 2017 study evaluated serum levels among a population of older California women during a four-year period, starting approximately five years after PBDEs were banned. Researchers found that from 2011-2015, previously reported declines in PBDE levels may have plateaued and may be again starting to increase.  Read more here.
     

  • Researchers evaluated whether address data from LexisNexis, a commercially available credit reporting company, could be used to reconstruct residential history for CTS participants. Using LexisNexis address data, researchers doubled the proportion of the study population of whom they had an address of residence during childbearing years, an important period of susceptibility for breast cancer risk.  Read more here.
     

  • Polyfluoroalkyl substances (PFASs), once commonly used, were phased out due to their bioaccumulative and toxic properties. When researchers evaluated the serum of middle-aged or older California women (ages 40-94) during a four-year period beginning approximately 5-10 years after these phase-outs began, they discovered that PFAs levels decreased an average of 10-20% a year, suggesting that the phase-out of PFAs effectively reduced human exposure to them. The only exception was PFA perfluorohexanesulfonic acid (PFHxS), of which levels did not significantly decline.  Read more here.
     

  • A 2018 study found no evidence that serum polyfluoroalkyl substances (PFASs) measured post-diagnosis had any relation to breast cancer risk.  Read more here.
     

  • Researchers compared the blood serum of women diagnosed with invasive breast cancer and women with no diagnosis. Using post-diagnostic data, researchers did not find evidence that higher PBE-related chemical (BDE-47, BDE-100, and BDE-153) presence in blood was associated with increased breast cancer risk.  Read more here.

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