In a recent study, researchers claim that high exposure to night lighting promotes one of the most common forms of thyroid cancer. These results need to be confirmed, but seem to confirm the harmful impact of artificial light on the body.

Artificial, light, at, night, increases, the, risk, of, thyroid, cancer

In addition to air pollution, city dwellers are also exposed to light pollution caused by excessive artificial lighting. However, its consequences are not limited to the deprivation of observation of the starry sky: it represents a source of disturbance for biodiversity but also a danger to health. According to Adème, light has an inhibiting effect on the secretion of melatonin, which disrupts the body's rhythms and all related functions, causing, for example, sleep disorders. Similarly, more and more recent studies show links between artificial night lighting and health disorders, such as depression or weight gain.

A new study published in the journal Cancer warns that people living in areas with high levels of artificial outdoor light at night may face a higher risk of developing thyroid cancer. Researchers at the University of Texas Health Sciences Center at the Houston School of Public Health found that previous studies have suggested an association between high levels of nighttime light measured by satellite and a higher risk of breast cancer. However, "some breast cancers may share a common hormone-dependent basis with thyroid cancer. "They explain.

Twice the risk in case of high exposure

They therefore looked for an association between artificial light at night and a subsequent risk of thyroid cancer among participants in a study called "NIH-AARP Diet and Health", which recruited American adults aged 50 to 71 years in 1995-1996. Investigators analyzed satellite imagery data to estimate nighttime lighting levels at participants' residential addresses, before examining the National Cancer Registry databases to identify thyroid cancer diagnoses through 2011. Among 464,371 participants followed for an average of 12.8 years, 856 cases of thyroid cancer were diagnosed.

The researchers found that compared to participants in the lowest light quintile group at night, those in the highest quintile group had a 55% higher risk of developing thyroid cancer. The association was primarily related to the most common form of thyroid cancer, called papillary thyroid cancer, and was stronger in women. As the National Cancer Institute explains, "in more than 90 percent of cases, thyroid cancer develops from follicular cells. It is called follicular strain thyroid cancer, which has two forms: papillary or vesicular. »

Night light disturbs the internal clock

The scientific team also found that in women, the association was stronger for localized cancer with no evidence of spread to other parts of the body, while in men, the association was stronger for more advanced stages of cancer. But the study indicates that further 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. If this is confirmed, it will be important to understand the mechanisms underlying the relationship between night light and thyroid cancer," say the authors. The main hypothesis put forward is a disruption of the body's internal clock (circadian rhythms), a risk factor for various types of cancer.

Another hypothesis concerns the fact that artificial night light suppresses melatonin, considered to be a modulator of the activity of other hormones, estrogens, which can have important anti-tumor effects. "Our study is not designed to establish a causal link. As a result, we do not know whether higher levels of outdoor light at night lead to a higher risk of thyroid cancer. However, given the evidence that supports the role of nighttime light exposure and circadian rhythm disruption, we hope it will motivate further investigation into the relationship between nighttime light and cancer and other diseases. "The researchers note.

They conclude that, recently, efforts have been made in some cities to reduce light pollution. It will then be important to conduct further studies in these locations to assess whether and to what extent these efforts have had an impact on human health. It should be noted that according to the ARC Foundation for Cancer Research, thyroid cancers are rare: they represent only 2% of all cancers diagnosed each year in France, i.e. a little over 8,000 new cases per year. However, it is a disease that is constantly on the rise, a phenomenon that is essentially linked to more frequently used and more precise diagnostic techniques.