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New strategies to control iodine deficiency worldwide suggested
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PARIS — One-third of the world remains iodine deficient, and 30% of households do not have access to iodized salt, according to 2007 UNICEF estimates. Despite having proven solutions to combat iodine deficiency worldwide, successful interventions do not reach high-risk groups, such as pregnant women, children and infants, who are most vulnerable to iodine deficiency, Michael B. Zimmermann, MD, said at the International Thyroid Congress.
“Iodine deficiency is one of four clear global risk factors for impaired child development,” Zimmermann said at a symposium. “[Salt iodization] remains the most cost-effective way to deliver iodine and improve cognition in children. … We must focus these interventions early in the life cycle in order to get maximal benefit.”
Novel strategies
Zimmermann suggested three novel strategies to target vulnerable groups: newborn thyroid-stimulating hormone (TSH); measuring urinary iodine in infants; and using dried blood spot thyroglobulin in children to ensure that the beginning of the life cycle is covered with adequate intake.
Increasingly, more countries are beginning to conduct careful newborn screening for congenital hypothyroidism and “maybe it has come time that we use TSH in the field of iodine assessment,” Zimmermann said. Data have shown that serum TSH is increased in iodine-deficient infants during the first few weeks of life. In these instances, newborn TSH may be a sensitive indicator of even mild iodine deficiency in populations, he said. According to WHO, an increase in transient hypothyroidism indicated by TSH levels greater than 5 mU/L in whole blood collected 3 to 4 days after birth in more than 3% of newborns suggests iodine deficiency in a population.
“As we try to use TSH in infants, we can come up with consistent recommendations about assays and collection methods to get better consistency,” Zimmermann said.
Second, median urinary iodine is used as an indicator of iodine nutrition in school-aged children, so “why don’t we think about measuring urinary iodine concentrations in newborns?” he asked. Access to newborns within the first few days of birth is high in many countries.
Although sample collection may be a challenge in newborns, Zimmermann and colleagues in Switzerland developed a noninvasive pad collection system that uses a feminine hygiene pad, tested to ensure that it is clear of iodine, to aspirate urine from using a syringe. This method of collection is “completely noninvasive and well accepted.” A study in more than 1,200 children showed that median TSH increased from 77 mcg/L at baseline to 100 mcg/L 1 to 4 days after birth.
His final recommendation is a thyroglobulin assay for use on dried blood spots as a valuable indicator of iodine deficiency. This method assesses thyroid status, appears to be sensitive to recent changes in iodine intake, and is easy to collect and store. However, it may be a challenge to collect thyroglobulin in many nonindustrialized countries, Zimmermann noted. When he and colleagues studied use of this method in young children, they calculated a reference range of 4 mcg/L to 40 mcg/L. An international reference range and standard reference material for this method would be needed for implementation in newborns.
Generations at risk
It is estimated that 41 million newborns remain unprotected from learning disabilities related to iodine deficiency. Every day, more than 120,000 babies are born iodine deficient and are at risk for mental and physical retardation, according to estimates Zimmermann presented at the symposium.
“Do we need new strategies to control iodine deficiency in 2010?” Zimmermann asked. “I would argue that we do.” – by Katie Kalvaitis
For more information:
- Zimmermann MB. SY01. Thyroid in the face of changing iodine intake. Presented at: the 14th International Thyroid Congress; Sept. 11-16, 2010; Paris.