The first case-control study examining the association between cell phone use and thyroid cancer found elevated risks of thyroid cancer among heavier, long-term cell phone users.
At greater risk of thyroid cancer were individuals who used a cell phone for more than 15 years, for more than two hours per day, or for a greater number of lifetime hours. Also, those who made the most cell phone calls in their lifetime were at increased risk.
Men who used cell phones for more than 15 years had over twice the risk of thyroid cancer as compared to non-cell phone users after controlling for other factors. Women who used cell phones for more than two hours per day had a 52% greater risk of thyroid cancer as compared to non-cell phone users.
Although the key findings in this study were of borderline statistical significance, this may be due to the relatively small sample size, especially for males. The study included 462 histologically-confirmed thyroid cancer cases and 498 population-based controls. Also, the study did not control for cordless phone use which may be a risk factor for thyroid cancer.
The study, published online in the Annals of Epidemiology on October 29, was conducted by researchers from the Yale School of Medicine and the Connecticut Health Department.
The authors recommended more research since the results from this study may not be generalizable to current cell phone users due to changing technology and patterns of use (e.g., hands-free use, texting). The authors noted that smartphones were not in common use during the period prior to 2010-2011 when the data for this study were collected. The majority of study participants did not start using cell phones until age 21. Future research should determine if the age of first cell phone use is associated with greater thyroid cancer risk.
The authors reported that thyroid cancer is the fastest growing cancer in the U.S. Incidence has nearly tripled since the 1980’s from four per 100,000 in 1980 to fifteen per 100,000 in 2014 making this the fifth most common cancer among women in the country. Although over-diagnosis is believed to account for about half of this increase, the remainder is likely due to changing environmental and lifestyle factors.
Yawei Zhang, MD, PhD, of the Yale School of Medicine and Cancer Center, was the senior author of this paper. The research was supported by the American Cancer Society, the U.S. National Institutes of Health, and the Ministry of Science and Technology of the People’s Republic of China.
My comments: The National Cancer Institute (NCI) estimates that 53,990 new cases of thyroid cancer will be diagnosed in 2018 making this the 12th most common cancer in the U.S. Rates for new thyroid cancer cases have increased 3.1% per year over the last ten years (on average) based upon an analysis of data from the NCI Surveillance, Epidemiology, and End Results-9 (SEER-9) cancer registry program.
Since smartphones are more likely to have cell antennas located in the bottom of the phones than earlier cell phone models, the peak radiation exposure from a smartphone is more likely in the neck than in the brain. Hence, I would hypothesize that the association between cell phone use and thyroid cancer has increased in recent years. The switch from “candy bar" and flip phones to smartphones could explain upward trends over time in thyroid cancer incidence and relatively flat trends in brain cancer observed in some countries.
Luo J, Deziel NC, Huang H, Chen Y, Ni X, Ma S, Udelsman R, Zhang Y. Cell phone use and risk of thyroid cancer: a population-based case control study in Connecticut. Annals of Epidemiology. Published online Oct 29, 2018. https://doi.org/10.1016/j.annepidem.2018.10.004.
Purpose. This study aims to investigate the association between cell phone use and thyroid cancer.
Methods. A population-based case-control study was conducted in Connecticut between 2010 and 2011 including 462 histologically confirmed thyroid cancer cases and 498 population-based controls. Multivariate unconditional logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (95% CI) for associations between cell phone use and thyroid cancer.
Results. Cell phone use was not associated with thyroid cancer (OR: 1.05, 95% CI: 0.74-1.48). A suggestive increase in the risk of thyroid microcarcinoma (tumor size ≤10mm) was observed for long-term and more frequent users. Compared to cell phone non-users, several groups had non-statistically significantly increased risk of thyroid microcarcinoma: individuals who had used a cell phone >15 years (OR: 1.29, 95% CI: 0.83-2.00), who had used a cell phone >2 hours per day (OR: 1.40, 95% CI: 0.83-2.35), who had the most cumulative use hours (OR: 1.58, 95% CI: 0.98-2.54), and who had the most cumulative calls (OR: 1.20, 95% CI: 0.78-1.84).
Conclusion. This study found no significant association between cell phone use and thyroid cancer. A suggestive elevated risk of thyroid microcarcinoma associated with long-term and more frequent uses warrants further investigation.