Exposure to high levels of outdoor artificial light at night may raise the risk of developing thyroid cancer, as per the study published in CANCER, a peer-reviewed journal of the American Cancer Society. Over the past century, nightscapes--especially in cities--have drastically changed due to the rapid growth of electric lighting. Also, epidemiological studies have reported an association between higher satellite-measured levels of nighttime light and elevated breast cancer risk.
‘Recently, there have been efforts in certain cities to reduce light pollution, and future studies should evaluate if and to what degree such efforts impact human health.’
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Because some breast cancers may share a common hormone-dependent basis with thyroid cancer, a team led by Qian Xiao, PhD, of The University of Texas Health Science Center at Houston School of Public Health, looked for an association between light at night and later development of thyroid cancer among participants in the NIH-AARP Diet and Health Study, which recruited American adults aged 50 to 71 years in 1995-1996.Read More..
The investigators analyzed satellite imagery data to estimate levels of light at night at participants' residential addresses, and they examined state cancer registry databases to identify thyroid cancer diagnoses through 2011.
Among 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). When compared with the lowest quintile of light at night, the highest quintile was associated with a 55 percent higher 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 stronger for localized cancer with no sign of spread 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 across participants with different sociodemographic characteristics and body mass index.
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Also, light at night may lead to disruption of the body's internal clock (or circadian rhythms), which is a risk factor for various types of cancer.
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"Recently, there have been efforts in some cities to reduce light pollution, and we believe future studies should evaluate if and to what degree such efforts impact human health."
Source-Eurekalert