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Effect of salt reduction on iodine status assessed by 24 hour urinary iodine excretion in children and their families in northern China: a substudy of a cluster randomised controlled trial
  1. Feng J He1,
  2. Yuan Ma1,2,3,
  3. Xiangxian Feng4,
  4. Wanqi Zhang5,6,
  5. Laixiang Lin6,7,
  6. Xiaohui Guo5,
  7. Jing Zhang2,
  8. Wenyi Niu8,
  9. Yangfeng Wu2,3,9,
  10. Graham A MacGregor1
  1. 1Wolfson Institute of Preventive Medicine, Barts and The London School of Medicine & Dentistry, Queen Mary University of London, London, UK
  2. 2The George Institute for Global Health at Peking University Health Science Center, Beijing, China
  3. 3Department of Epidemiology and Biostatistics, Peking University School of Public Health, Beijing, China
  4. 4Changzhi Medical College, Shanxi, China
  5. 5School of Public Health, Tianjin Medical University, Tianjin, China
  6. 6Key Laboratory of Hormone and Development (Ministry of Health), Tianjin, China
  7. 7Metabolic Diseases Hospital & Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin, China
  8. 8Department of Social Medicine and Health Education, Peking University School of Public Health, Beijing, China
  9. 9Peking University Clinical Research Institute, Beijing, China
  1. Correspondence to Dr Feng J He; f.he{at} Professor Wanqi Zhang;


Objective To study the effect of salt reduction on iodine status and to determine whether iodine consumption was still adequate after salt reduction in a population where universal salt iodisation is mandatory.

Design A substudy of a cluster randomised controlled trial, with schools randomly assigned to either the intervention or the control group.

Setting 28 primary schools in Changzhi, northern China.

Participants 279 children in grade 5 of primary school (mean age: 10.1); 553 adults (age: 43.8).

Intervention Children were educated about the harmful effects of salt and how to reduce salt intake using the schools' usual health education lessons. Children then delivered the message to their families. The duration was 1 school term (≈3.5 months).

Main outcome measure Difference between the intervention and control groups in the change of iodine intake as measured by repeat 24 hour urinary iodine from baseline to the end of the trial.

Results At baseline, the mean salt intake was 7.0±2.5 g/day in children and 11.7±4.4 g/day in adults and the median iodine intake was 165.1 μg/day (IQR: 122.6–216.7) and 280.7 μg/day (IQR: 205.1–380.9) in children and adults, respectively. At the end of the study, salt and iodine decreased in the intervention compared with control group. The mean effect on salt for intervention versus control was −1.9 g/day (95% CI −2.6 to −1.3) in children and −2.9 g/day (95% CI −3.7 to −2.2) in adults. The mean effect on iodine was −19.3% (95% CI −29.4% to −7.7%) in children and −11.4% (95% CI −20.3% to −1.5%) in adults.

Conclusions With ≈25% reduction in salt intake, there was a significant reduction in iodine consumption in northern China where salt is iodised. Despite this, iodine intake was still adequate, and well above the estimated average requirement. Our findings indicate that reducing salt to the WHO's target—30% reduction by 2025—will not compromise iodine status.

Trial registration number NCT01821144.

  • Salt reduction
  • Iodine status
  • 24h urine collections
  • Cluster randomised trial

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