Definition: Student iodine status refers to the level of iodine nutrition, primarily assessed through urinary iodine concentration (UIC), in school-aged children (typically 6-12 years). This group is a key monitoring population recommended by the WHO, UNICEF, and IGN, as they are easily accessible, represent the general community, and are highly sensitive to iodine deficiency.
Core Importance: Iodine is essential for the production of thyroid hormones, which are critical for normal growth, development, and metabolism. In students, adequate iodine is crucial for optimal cognitive function, learning ability, and physical development. Even mild iodine deficiency can impair intellectual performance and school achievement.
In summary, monitoring student iodine status is a vital public health tool. It reflects the iodine nutrition of a population and directly correlates with a key outcome—the cognitive potential and healthy development of the next generation. Maintaining optimal iodine status in students is a cost-effective investment in human capital.
- iodine nutrition
- children
- iodine deficiency disorders
- goiter
- thyroid enlargement
1. Introduction and Core Importance
Iodine is an essential micronutrient required for the synthesis of thyroid hormones (T4andT3), which regulate metabolism, somatic growth, and neurological development [1][1].
- Cognitive Impact:In students, adequate iodine status is a determinant of cognitive potential. Deficiency is the leading cause of preventable intellectual disability globally. Even mild deficiency in this age group can correlate with reduced Intelligence Quotient (IQ) and impaired school performance.
- Physical Impact:Chronic deficiency leads to goiter (thyroid enlargement) and growth retardation.
2. Assessment Methodologies
The assessment of student iodine status typically involves a cross-sectional survey using three primary indicators:
2.1. Median Urinary Iodine Concentration (mUIC)
Since >90% of dietary iodine is excreted in urine, mUIC is the most sensitive biomarker for recent intake.
- WHO/UNICEF Criteria (School-Age Children):
- < 100μg/L:Insufficient (Iodine Deficiency).
- 100–299μg/L:Adequate (Optimal).
- ≥300μg/L:Excessive (Risk of autoimmune thyroiditis).
2.2. Thyroid Volume (Goiter Rate)
Thyroid volume is measured via ultrasound to assess long-term iodine nutrition.
- Goiter:Defined as a thyroid volume exceeding the 97th percentile of age- or body-surface-area-specific reference values. A total goiter rate (TGR) >5% in students indicates a public health problem.
2.3. Household Salt Iodine
Monitoring the iodine content of salt consumed in students' households ensures the effectiveness of Universal Salt Iodization (USI) programs.
3. Current Trends: The "Adequate but Declining" Phenomenon
While USI has been highly effective globally, recent epidemiological data suggest a shifting landscape due to lifestyle changes. A notable phenomenon is thedecline in student iodine levels despite stable salt iodization, driven by salt reduction policies and dietary shifts.
3.1. Case Study: Trends in Chongqing, China
A prominent example of this trend is observed in Chongqing, a major municipality in China. According to a 2025 study by Pang et al [2][1]. published in Nutrients:
- Longitudinal Decline:The median UIC in school-age children has shown a clear downward trajectory over the past two decades, dropping from 303.0μg/L in 1997 to 226.4μg/L in 2023.
- Current Status:Although the current level (226.4μg/L) remains well within the "Adequate" range (100–299μg/L), the decline highlights the impact of dietary transitions.
- Drivers:This reduction is attributed to the implementation of national "Salt Reduction" campaigns (aiming for <5g salt/day) and the increased consumption of processed foods, which often contain non-iodized salt. This case illustrates the potential conflict between cardiovascular health goals (less salt) and iodine maintenance.
4. Gender Disparities
Research consistently identifies biological sex as a variable in student iodine status.
- Boys vs. Girls:Studies, including the Chongqing cohort, typically observe that boys have higher urinary iodine excretion than girls. This is widely attributed to boys consuming larger quantities of food (and thus more iodized salt) to support higher basal metabolic rates.
- Thyroid Health:Despite adequate iodine status, girls often present with higher rates of thyroid enlargement (goiter) or nodules compared to boys, suggesting that female students may have a higher physiological sensitivity or autoimmune predisposition that requires gender-specific monitoring.
5. Public Health Implications
Monitoring student iodine status is no longer just about detecting deficiency; it now involves ensuring balance.
- Blind Spots:Relying solely on household salt monitoring is insufficient. As students consume more meals outside the home (e.g., school cafeterias, processed snacks), their total iodine intake may decrease even if household salt is fully iodized.
- Integrated Policies:Public health strategies must align salt reduction targets with iodine fortification levels to prevent re-emergence of deficiency.
References
- Zimmermann, M.B. Iodine deficiency. Rev.2009,30, 376–408.
- Pang, P.; Xie, J.; Yang, M.; Zhou, S.; Zhang, Y., China.Nutrients2025,17, 817.