MADRID, 8 Feb. (EUROPA PRESS) –
People who live in regions with high levels of artificial light outdoors at night may be at increased risk of developing thyroid cancer, according to a study published early online in CANCER, a peer-reviewed journal of the American Cancer. Society.
During the past century, night landscapes, especially in cities, have changed dramatically due to the rapid growth of electric lighting. Additionally, epidemiological studies have reported an association between higher levels of night light measured by satellite and an elevated risk of breast cancer.
Because some breast cancers may share a common hormone-dependent basis with thyroid cancer, a team led by Qian Xiao, of the University of Texas Health Sciences Center at the Houston School of Public Health, sought a partnership. between night light and later development of thyroid cancer among participants in the NIH-AARP Health and Diet Study, which enrolled American adults ages 50 to 71 in 1995-1996.
The researchers analyzed satellite image data to estimate nighttime light levels in the participants’ residential addresses.
Among the 464,371 participants who were followed for an average of 12.8 years, 856 cases of thyroid cancer were diagnosed (384 in men and 472 in women). Compared to the lowest quintile of night light, the highest quintile was associated with a 55 percent increased risk of developing thyroid cancer.
The association was primarily driven by the most common form of thyroid cancer, called papillary thyroid cancer, and it was stronger in women than in men. In women, the association was strongest for localized cancer without signs of spreading to other parts of the body, while in men the association was stronger for more advanced stages of cancer.
The association appeared to be similar for different tumor sizes and between participants with different sociodemographic characteristics and body mass index.
The researchers noted that additional epidemiological studies are needed to confirm their findings. If confirmed, it will be important to understand the mechanisms underlying the relationship between night light and thyroid cancer.
The scientists found that night light suppresses melatonin, a modulator of estrogen activity that can have important antitumor effects. Additionally, light at night can cause the body’s internal clock (or circadian rhythms) to be disrupted, which is a risk factor for several types of cancer.
“As an observational study, our study is not designed to establish causality. Therefore, we do not know whether higher levels of outdoor light at night lead to an elevated risk of thyroid cancer; however, given the well-established evidence supporting a role for nighttime light exposure and circadian alteration, we hope our study will motivate researchers to further examine the relationship between nighttime light and cancer and other diseases, “explains Dr. Xiao.
“Recently, there have been efforts in some cities to reduce light pollution, and we believe that future studies should assess whether and to what extent those efforts have an impact on human health,” they recommend.
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