Background Urinary iodine concentration (UIC) is routinely used to evaluate the population iodine status while the uniform method for the individual level assessment is uncertain. Objectives To explore the 24-h urinary iodine excretion (UIE) in five different periods of the day and the corresponding prediction equations respect by the use of creatinine-corrected UIC. Methods We collected 24-h, spot and fasting urine in five periods of the day to estimate 24-h UIE by the six different prediction equations. We compared the estimated creatinine-corrected UIC to the collected 24-h UIE and identified the most suitable equations in each period of the day. Results Among the six different prediction equations, the equation of Kawasaki T was the best to estimate the 24-h UIE by fasting urine among Chinese adults. Among the five periods of time, the equation of Knudsen N was the best to estimate the 24-h UIE in the non-morning period. Conclusion Urinary iodine status at the individual level could be estimated by different creatinine-based equations at different periods of the day.

Background The prevalence of thyroid nodules has been increasing in recent years. Nevertheless, studies on the association between iodine status and thyroid nodules are controversial. Objective We aimed to investigate whether there is an association between iodine status and thyroid nodule disease and explore the risk factors of thyroid nodules. Methods 3926 residents participated in the investigation from the four different regions in Fujian Province in 2017, which are coastal urban area (CUA), non-coastal urban area (Non-CUA); coastal rural area (CRA), and non-coastal rural area (Non-CRA). Participants were interviewed face-to-face using a structured questionnaire. B-ultrasound was carried out to detect thyroid nodules, and drinking water, table salt, and urine samples were collected from the household. Results The iodine status was appropriate in Fujian Province. The prevalence of thyroid nodules was 22.4% in 2017, of which males accounted for 16.3% while females accounted for 28.2%. In our study, there was no statistically significant between iodine status and thyroid nodules (P > 0.05). However, female (OR = 1.9), increasing age (OR = 1.1), housewife (OR = 1.4); student (OR = 4.2); employee of enterprises and institutions (OR = 1.5), less frequency of milk and dairy products intake (< 3 times (3t) per week: 1-2t OR = 2.7; <1t OR = 2.3), and less frequency of vegetables and fruits consumption intake (< 3 times (3t) per week: 1-2t OR = 1.4; <1t OR = 1.4) are risk factors for thyroid nodule disease (P < 0.05). Conclusions There was no evidence indicating that drinking water, iodized salt, iodine-rich food, goitrogenic food, and urinary iodine concentration (UIC) are connected with thyroid nodules. Females, increasing age,, vocation (student, housewife, employee of enterprises and institutions), less frequency of milk and dairy products intake (< 3t per week), less frequency of vegetables and fruits consumption intake, and living in coastal city (coastal or urban) can increase the risk of thyroid nodules.