In a new study, researchers found that people living in regions with high levels of outdoor artificial light at night may face a higher risk of developing thyroid cancer.
The research was conducted by a team at the University of Texas.
Previous studies have reported a link between higher satellite-measured levels of nighttime light and elevated breast cancer risk.
Because some breast cancers may share a common hormone-dependent basis with thyroid cancer, the team in the study examined a link between light at night and later development of thyroid cancer.
The data were from the NIH-AARP Diet and Health Study, which recruited American adults aged 50 to 71 years in 1995-1996.
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 linked to a 55% 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 link 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.
If the findings are confirmed, it will be important to understand the mechanisms underlying the relationship between light at night and thyroid cancer.
The scientists noted that light at night suppresses melatonin, a modulator of estrogen activity that may have important anti-tumor effects.
Also, the 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.
One author of the study is Qian Xiao, Ph.D.
The study is published in Cancer.