Salt restriction could increase risk of iodine deficiency

Nearly a third of Americans have hypertension, a risk factor for heart disease and stroke, according to the Centers for Disease Control and Prevention (CDC). Excessive sodium consumption has repeatedly been linked to high blood pressure, and Americans consume on average about 4,000mg a day – far more than the 2,300mg recommended in the 2005 Dietary Guidelines for Americans.

In addition, the CDC recommends that 69 percent of the population – including blacks, those aged 40 or older, and those with high blood pressure – should limit their sodium intake to 1,500mg a day, as these groups are at particular risk of health problems arising from consuming too much sodium.

However, the United States’ salt supply is fortified with iodine, deficiency of which can lead to hypothyroidism, infertility, thyroid cancer, goiter, poor cognition, lethargy, and decreased labor productivity in adults.

“Restriction of dietary salt consumption as a treatment option for hypertension could mean a significant curtailing of iodine intake and hence risk of iodine deficiency,” ​the study’s authors wrote.

Iodine deficiency prevalence​

The researchers examined data from the 2001–2004 National Health and Nutrition Examination Surveys (NHANES) for associations between hypertension, salt restriction and iodine deficiency in a sample of 996 men and 960 women.

They found that hypertensive women were more successful than men in restricting their salt intake – with 41.8 percent of women in the study sample who were trying to restrict salt consuming a moderate amount of sodium (2,400mg a day or less), compared to 26.1 percent of men who aimed to restrict salt. More men than women reported restricting salt intake – 13.6 percent compared to 12.8 percent.

Across the study sample, 25 percent of men and 40.4 percent of women were found to be iodine deficient.

“Dietary salt restriction associated with iodine deficiency among women but not among men. Alternative sources of iodine should be suggested to those who need to cut dietary salt for hypertension and for other health reasons,”​ the researchers concluded.

Salt fortification​

Iodization of salt was introduced in the United States in 1924 in order to curb iodine deficiency disorders, and was voluntarily taken up shortly afterwards. Today, the Food and Drug Administration (FDA) mandates fortification of salt with iodine in the form of potassium iodide or copper iodide at a level of 0.01 percent.

“Taking cognizance of intake levels, food processing effects, and cooking losses, this level of fortification could contribute about 50 μg iodine to the average person’s daily iodine need of 150 μg,”​ the authors wrote.

Food manufacturers have taken strides to slash sodium from their products in recent years, as they have come under pressure to do so from public health and governmental bodies. An estimated 70 to 80 percent of American sodium consumption comes from packaged foods.

Source: American Journal of Hypertension​

October 2010, Vol. 23, No. 10, pp. 1095-1102

“Hypertension, Dietary Salt Restriction, and Iodine Deficiency Among Adults”​

Authors: Francis A.K. Tayie and Katie Jourdan