Study says table salt may not have as much iodine as labeled
■ Intake of this mineral has declined, although not to levels that would cause problems. One researcher wants to mandate including this substance in all salt.
By Victoria Stagg Elliott — Posted March 3, 2008
The iodine content in table salt may not match its label, and amounts may vary throughout the container, according to a study published in the Feb. 15 Environmental Science & Technology.
"There's a problem here," said Purnendu K. Dasgupta, PhD, lead author and chair of the chemistry department at the University of Texas at Arlington.
Iodization of table salt, considered one of the great public health achievements of the 20th century and widely supported by the American Medical Association as well as many other public health organizations, is common but not mandated. Much of the salt used in processed food may not have this additive, and, according to the study, more than half of table salt samples did not contain enough of it. In response to these data and the fact that the average American diet is composed of an increasing amount of processed food, the authors are calling for all salt to be iodized.
"If you iodize all the salt then you would automatically increase iodine consumption without increasing salt consumption," said Dr. Dasgupta. "We need to have legislative action."
This perspective is also in response to concerns that iodine levels in the U.S. diet have diminished. Centers for Disease Control and Prevention statistics indicated that consumption of the mineral declined by more than 50%, based on comparisons between the 1971 to 1974 National Health and Nutrition Examination Survey and the one conducted from 1988 to 1994. Subsequent surveys found the number had stabilized, and public health officials and advocates of appropriate iodine consumption are continuing to monitor the situation.
"If it continued to drop, that would not be a good thing," said Jonathan Borak, MD, clinical professor of epidemiology and public health at Yale University in New Haven, Conn.
Worry is particularly acute with regard to pregnant women because deficiency of the mineral can affect fetal and newborn development.
For example, a study in the May 2007 Journal of Clinical Endocrinology & Metabolism found 47% of women who were breastfeeding were producing milk that did not have enough iodine for their infant.
The American Thyroid Assn. issued policy in April 2004 calling for pregnant women to take prenatal vitamins that include the mineral.Experts increasingly are calling for these products to always contain it, because not all do.
"This is when you need it the most, but you may not be getting it," said Elizabeth Pearce, MD, lead author on that paper and assistant professor of medicine at Boston University.
This phenomenon may be the result of educational efforts to reduce overall salt intake because of the cardiovascular risk associated with ingesting large amounts of sodium, as well as changes in food production that mean iodine is not as present as it used to be. In addition, people are more likely to get their salt from processed food, in which salt is not always iodized, than from table salt, which usually is iodized.
"I suspect that iodized salt is not the primary way we get iodine in our diet any more," said Dr. Pearce. "And we cannot count on salt as the sole source of dietary iodine."
But those who work in the salt industry doubt that the reductions in iodine in the American diet are the result of the varying levels in table salt found by this study and questioned the soundness of the researchers' methods.
"There's absolutely no chance that our salt is not within the Food and Drug Administration specifications for iodine," said Richard L. Hanneman, president of the Salt Institute.
Also, although consumption of iodine has gone down, there are no data that the general population has actually become deficient in this substance. A paper published by FDA researchers online last month in the Journal of Exposure Science & Environmental Epidemiology concluded that iodine intake was high enough.