Prevalence of thyroid nodules and its association with water iodine among Chinese men and women

Because of the large change in iodine nutrition and other lifestyle in China, there is concern that thyroid nodules (TNs) may become epidemic. However, few data are currently available on the national prevalence of TNs. In addition, whether excess iodine in drinking water is associated with an increased risk of TNs, following universal salt iodization, has been less studied. We aim to estimate a national prevalence of TNs and its association with drinking water iodine.We conducted a national survey of 9,381,032 adults, aged 18 years or older, from 30 provinces and municipalities in China, who underwent a thyroid ultrasound test from January 2018 to December 2018. Crude and standardized prevalence of TNs were estimated. We further evaluated the ecological association between province- or city-specific iodine levels in drinking water and the prevalence of TNs using linear regression.The age-standardized prevalence of TNs in men, women, and both sexes were 29.8%, 44.7%, and 37.1%, respectively. The prevalence increased with age from 22.7% (18-30 years) to 71.5% (≥70 years), and body mass index from 26.1% (<18.5 kg/m2) to 40.8% (≥28 kg/m2). Participants living in the eastern, northern, and northeastern regions had a higher prevalence of TNs (ranged from 38.7% to 43.7%) than those in other regions (ranged from 30.1% to 35.5%). The coastal residents (40.1%) had a higher prevalence of TNs than those in inlanders (35.4%). Higher levels of iodine in drinking water were linearly associated with increased prevalence of TNs, with Pearson correlation coefficients of 0.47 (P < 0.01) in men, 0.40 (P = 0.03) in women, and 0.46 (P = 0.01) in overall participants.This was a nationwide prevalence study of TNs in China, showing that TNs were common health problems, and increased concentration of iodine in drinking water was associated with a higher prevalence of TNs.