A startling new study suggests that iodine deficiency, the most common cause of brain damage worldwide, could be rampant in the UK even though it is one of the easiest and least expensive nutrient disorders to prevent, according to the World Health Organization.
Writing in the journal The Lancet, researchers reported that 70 percent of UK girls age 14-15 could have a deficiency of iodine, which is essential to maintaining thyroid hormone function and occurs naturally in seawater and soil.
Half of the 800 some teenagers they surveyed displayed a mild iodine deficiency, while 15 percent were found to be moderately deficient -- a classification the authors say has been linked to population-wide IQ declines of up to 15 points.
At least 1 percent of those surveyed were found to be severely iodine deficient, which is additionally concerning given that the women could become pregnant in the mid- to long-term, the authors warned. Iodine deficiencies can cause problems like goiters, the swelling of the thyroid gland, and cognitive decline throughout the life cycle, but pregnant women are particularly susceptible to possible negative effects. Adequate levels of iodine are critically important for neural development in utero.
"It seems unconscionable that a country with the resources of the UK should be iodine-deficient in 2011," Dr. Elizabeth Pearce, an endocrinologist with Boston University's School of Medicine wrote in a commentary accompanying the study. "How did this happen?"
One possible culprit is salt.
Although it has never been mandated here, a large majority of all table salts sold in the U.S. are iodized, a practice that began in the 1920s.
"We estimate that about 70 percent of all table salts sold in the U.S. are iodized," said Mark O'Keefe, director of communications for the trade organization Salt Institute, who also hailed the process as one of the most effective dietary interventions of the 20th century. He cautioned, however, that that figure excludes the salt used in commercial foods, which are often not iodized, as well as many sea salts.
In the UK, access to iodized salt is far more limited. In her accompanying commentary, Pearce estimated that less than 5 percent of salt sold in the UK is iodized, which could go a long way in explaining the lower iodine levels.
Another major source of dietary iodine is dairy milk.
In the 1930s, iodine was added to cattle feed to improve milk production. This "unplanned contaminant," as Pearce describes it, had the happy effect of upping the iodine levels in dairy milk -- so much so that in the mid 1990s, researchers estimated it accounted for approximately 40 percent of the iodine intake in the UK.
Now, researchers of the new study cite declines in milk drinking as a possible source of iodine deficiency.
"We believe that the findings of this survey have huge public health importance for the UK," said Dr. Mark Vanderpump, an endocrinologist with the Royal Free Hampstead NHS Trust and the study's lead author. Pearce echoed that sentiment, writing that it will take time for public health officials to develop a comprehensive strategy addressing the deficiency. She argued that the UK should make the iodization of salt mandatory and in the meantime urged women who are pregnant or who could become pregnant to take a daily vitamin supplement that contains iodine.
Pearce also cautioned that the new study could have implications for the U.S.
"The CDC has been measuring iodine at intervals since the 1970s and at one point in the 1990s they dropped by 50 percent, which was never fully explained" she said in an interview. "Things seem to have stabilized, but there's some concern, now, that especially among that subset of women of childbearing age, there could be a mild deficiency, too."