The researchers compared satellite image data – to estimate the night light at each participant’s address – with data from state cancer registries up to 2011.
They found 856 cases of thyroid cancer among the more than 464,000 participants, all of whom were followed for an average of 13 years. These cases included 384 men and 472 women.
The researchers reported that people who lived in areas with the highest 20% category of night light were 55% more likely to develop thyroid cancer than people who lived in the lowest 20% category. The risk was seen primarily for the most common form of thyroid cancer, papillary thyroid cancer.
The researchers also found that the association was stronger in women than in men. They found that in women, the association was stronger with localized cancers that showed no evidence of spreading to other parts of the body.
In men, the association was stronger with more advanced cancer stages. The association was similar for different tumor sizes and participant demographics, including sociodemographics and body mass index (weight).
How could light at night cause thyroid cancer?
According to Xiao’s group, night light suppresses natural melatonin, a modulator of estrogen activity. Too little melatonin activity could contribute to impairing the body’s ability to fight off tumors. Light at night can also disrupt the body’s circadian rhythms, which is also a cancer risk factor, the researchers said.
Dr. Shuchie Jaggi is an endocrinology, diabetes, and metabolism doctor at Northwell Health in Great Neck, New York. Reading the results, she said it was possible that night light may affect the thyroid through its effects on hormones and “certainly the large sample size” of this study is a strength that makes these associations statistically significant. “
Jaggi noted that the study had a flaw: because it relied on satellite imagery, it could only examine the exterior lights at night, not whether people were leaving their interior lights on.
For his part, Har-El said this is only “the first study to look at this aspect of advanced technology affecting our lifestyles, and it is only a study,” so much more research is needed.
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