Studies Examine U.S. Salt Intake over 50 Years, Iodine Deficiency
A recent study has reportedly claimed that dietary salt intake has remained constant in the U.S. population for the past five decades, raising questions about government efforts to restrict sodium consumption. Adam Bernstein and Walter Willett, “Trends in 24-h urinary sodium excretion in the United States, 1957–2003: a systematic review,” American Journal of Clinical Nutrition, November 2010. Researchers examined data on urine sodium excretions collected from 26,271 individuals by 38 MEDLINE studies published between 1957 and 2003. “In a multivariate random-effects model with study year, sex, age, and race, the study year was not associated with any significant change in sodium excretions,” states the abstract, which concludes that “[s]odium intake in the US adult population appears to be well above current guidelines and does not appear to have decreased with time.”
The study was accompanied by an editorial questioning the effectiveness of
a U.S. sodium reduction policy that targets, not just at-risk individuals, but
“the population at large.” Titled “Science Trumps Politics: Urinary Sodium Data
Challenge US Dietary Sodium Guidelines,” the editorial resists the tendency
to blame the government’s failure on “the food industry’s excessive use of
sodium in their products.” As the article claims, “Both the application of such
a government policy to the entire population and the simplistic assessment
that its failure to date can be attributed to the food industry’s reluctance
to provide lower sodium foods belie the scientific complexity of the issues,
including sodium’s role in health and disease.”
Citing their own previous research, the editorial’s authors support the latest findings and suggest that salt consumption “is not a readily modifiable nutritional parameter for the population at large.” They also note that although a reduction in food sodium content might theoretically reduce individual salt consumption, “the reality [is] that, over the millennia, before the introduction of processed foods, sodium was added to foods at the time of preservation, cooking, or consumption. An individual in our society has the identical options today as the food industry moves to offering more products whose ratio of calories to sodium is increased (ie, lower sodium content per serving). This individual choice could abrogate any effect on average sodium intake in society as these data indicate has happened.”
In a related development, a second study has evaluated “the association between dietary salt restriction and iodine deficiency among adults in the United States,” finding that women who restricted dietary salt intake were more likely to be iodine deficient. Francis Tayie and Katie Jourdan, “Hypertension, Dietary Salt Restriction, and Iodine Deficiency Among Adults,” American Journal of Hypertension, October 2010. Researchers apparently used multiple regression models to assess “the association between hypertension conditions, salt restriction and iodine deficiency among 996 men and 960 women” enrolled in the 2001-2004 waves of the National Health and Nutrition Examination Surveys (NHANES).
The study sample reportedly indicated that approximately 25 percent of men and 40 percent of women were iodine deficient, but that “salt restriction did not associate significantly with iodine deficiency among men.” Among women, however, those who restricted their dietary salt intake had “significantly lower urinary iodine concentration” than women who did not avoid salt. “Salt restriction associated with iodine deficiency among women but not men,” concluded the study authors, who recommended that physicians suggest alternative sources of iodine to women in particular.
