Chennai: In yet another indication that modern lifestyle is critical in developing diseases, a new study has suggested that people who are exposed to night sky brightness may face a higher risk of developing thyroid cancer.
Published in Cancer, a peer-reviewed journal of the American Cancer Society, the research found that light at night suppresses melatonin, a modulator of estrogen activity that may have important anti-tumour effects. 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.
Epidemiological studies have reported an association 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, a team led by Qian Xiao, 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.
The investigators analysed 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 per cent 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 localised 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 tumour sizes and across participants with different sociodemographic characteristics and body mass index.