A study of more than 464,000 participants over nearly 13 years shows that people living in areas with very strong outdoor artificial light at night have a higher risk of developing thyroid cancer.
- A large epidemiological study conducted over nearly 13 years among 464,000 American adults shows that strong artificial light at night was associated with a 55% higher risk of developing thyroid cancer.
Can lights from street lamps and shop windows at night increase the risk of developing thyroid cancer?
This is the conclusion reached by researchers at the University of Texas (USA). In a study published online in CANCERthe journal of the American Cancer Society, they explain that thyroid cancer, like breast cancer, can have a hormone-dependent origin, and that this can be fueled by strong electric lights.
A 55% higher risk
To reach this conclusion, the researchers recruited 464,371 American adults between the ages of 50 and 71 in 1995 and 1996, who were followed for an average of 12.8 years. They analyzed satellite imagery data to estimate nighttime light levels at participants, and examined state cancer registry databases to identify thyroid cancer diagnoses through 2011. .
During the follow-up period, 856 cases of thyroid cancer were diagnosed (384 in men and 472 in women). The researchers found that compared to the lowest quintile of nocturnal light, the highest quintile was associated with a 55% higher risk of developing thyroid cancer, including the most common form of cancer, called papillary thyroid cancer. .
They noted that this association between night light and papillary thyroid cancer was stronger in women than in men. Other differences were noted: in women, the association was stronger for localized cancers with no evidence of spread to other parts of the body, while in men, the association was stronger for later stages. advanced cancer.
Several causes considered
Further epidemiological studies are now needed to confirm the study’s findings. If confirmed, it will be important to understand the mechanisms underlying the relationship between night light and thyroid cancer. Two avenues are being considered: first, suppression by night light of melatonin, a modulator of estrogen activity that may have important anti-tumor effects. Second, nighttime light disrupts the body’s internal clock (or circadian rhythms), which is a risk factor for various types of cancer.
“As an observational study, our study is not designed to establish a causal relationship. 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 the role of nighttime light exposure and circadian rhythm disruption, we hope that our study will motivate researchers to further examine the relationship between nighttime light and cancer, and other diseasessays Dr. Xiao, lead author of the work. Recently, efforts have been made in some cities to reduce light pollution, and we believe that future studies should assess whether and to what extent these efforts impact human health.”
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