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Iodine status of Canadians, 2009 to 2011
Among Canadians aged 3 to 79, the median iodine concentration in urine was 1.06 micromoles per litre (µmol/L). A moderate deficiency of urine iodine levels was found in 7% of the population while 15% had an excessive intake.
Iodine deficiency is among the four major nutritional deficiencies in the world1 and can lead to several medical disorders, including goitre (swelling of the thyroid gland), stunted physical and intellectual development, stillbirths, and spontaneous abortions. These disorders have been virtually eliminated in Canada through salt iodization. However, care should be taken when consuming iodine-rich food, as excess iodine intake can also cause inhibitory effects on the thyroid gland which can lead to goitre.2 The World Health Organization (WHO) has established the optimal iodine concentration in urine required for nutritional sufficiency (Table 1).3
| Condition | Concentration of iodine in urine (µmol/L) |
|---|---|
| Moderate deficiency | Between 0.16 and 0.38 |
| Mild deficiency | Between 0.39 and 0.78 |
| Adequate intake | Between 0.79 and 1.57 |
| More than adequate intake | Between 1.58 and 2.36 |
| Excessive intake | 2.37 or above |
Iodine levels in Canada
Based on results from the Canadian Health Measures Survey (CHMS) the median iodine concentration of Canadians in 2009 to 2011 was 1.06 µmol/L (Chart 1), which is within the range of adequate intake recommended by the WHO. The median iodine concentration in urine was higher in children (1.70 µmol/L for 3 to 5 year olds and 1.49 µmol/L for 6 to 11 year olds) and decreased gradually with age to a median of 0.97 µmol/L in adults 20 years and older.
Chart 1
Median iodine concentration in urine, by age group, household population aged 3 to 79, Canada, 2009 to 2011
Source: Canadian Health Measures Survey, 2009 to 2011. The CHMS collects health information on the Canadian household population aged 3 to 79.
Iodine levels indicating a mild deficiency were found in 22% of Canadians aged 3 to 79 while a moderate deficiency was found in 7% (Chart 2). For children, only 2% of 3 to 5 year olds and 3% of 6 to 11 year olds had urine iodine levels indicating a moderate iodine deficiency, whereas this number was higher in adults (8% for 20 to 79 year olds). Recent North American surveys have shown an increasing prevalence of low iodine levels.4 This increase in low iodine levels could be attributed to a change in food production and consumption, such as a reduction of salt in the diet, the increasing popularity of non-iodized salt like sea salt, the reduction of iodine supplementation in commercial dairy products and the replacement of iodine with bromine salts as dough conditioner in breads.5, 6
The percentage of children and youth having an excessive urine iodine level (39%, 29% and 21% of children and youth aged 3 to 5, 6 to 11 and 12 to 19, respectively) was significantly higher than adults, based on the upper threshold of 2.37 µmol/L set by the WHO.3 These high levels could be attributed to dairy and grain products naturally rich in iodine that are consumed in higher portions by children than adults.
Chart 2
Percentage of the population with low and high urine iodine levels, by age group, household population aged 3 to 79, Canada, 2009 to 2011
E Use with caution (data with a coefficient of variation (CV) from 16.6% to 33.3%)
Source: Canadian Health Measures Survey, 2009 to 2011. The CHMS collects health information on the Canadian household population aged 3 to 79.
About iodine
Iodine is an essential component of several hormones produced by the thyroid gland. These iodine-rich thyroid hormones, such as thyroxine and triiodotyronine, are important in the development of the body and the brain, especially at a young age. Iodine is an element that is obtained from our diet, mainly from iodized salt, but also from natural sources, such as seafood, milk and grain products. The CHMS measured the iodine concentration in spot urine (in micromoles per litre - µmol/L) on a nationally representative population sample. Urine samples are used to measure iodine, as over 90% of iodine ingested in food and beverages is excreted in urine. Therefore, iodine levels in urine reflect the amount of iodine consumed and present in the body.7
References
- UNICEF. The state of the world's children. London: Oxford University Press; 1995.
- Zimmerman M, Ito Y, Hess SY, Fujieda K, Molinari L. High thyroid volume in children with excess dietary iodine intakes. American Journal of Clinical Nutrition. 2005;81(4):840-4.
- de Benoist B, Andersson M, Egli I, Takkouche B, Allen H, eds. Iodine status worldwide: WHO global database on iodine deficiency. Geneva: Department of Nutrition for Health and Development - World Health Organization; 2004.
- Caldwell KL, Jones R, Hollowell JG. Urinary iodine concentration: United States National Health and Nutrition Examination Survey 2001-2002. Thyroid. 2005;15(7):692-9.
- Hollowell J, Staehling NW, Hannon WH, et al. Iodine nutrition in the United States. Trends and public health implications: iodine excretion from the National Health and Nutrition Examination Surveys I and III (1971-1974 and 1988-1994). Journal of Clinical Endocrinology & Metabolism. 1998;83(10):3401-8.
- Pennington JA, Shoen SA. Contributions of food groups to estimated intakes of nutritional elements: results from the FDA total diet studies, 1982-1991. International Journal for Vitamin and Nutrition Research. 1996;66(4):342-9.
- Nath SK, Moinier B, Thuillier F, Rongier M, Desjeux JF. Urinary excretion of iodide and fluoride from supplemented food grade salt. International Journal for Vitamin and Nutrition Research. 1992;62(1):66-72.
For more information on the Canadian Health Measures Survey, please contact Statistics Canada's National Contact Centre (toll-free 1-800-263-1136; 613-951-8116; infostats@statcan.gc.ca).
