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The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States.

ABSTRACT: Iodine deficiency is the leading cause of preventable mental retardation in the world today. The condition, which was common in the developed world until the introduction of iodized salt in the 1920s, is connected to low iodine levels in the soil and water. We examine the impact of salt iodization on cognitive outcomes in the US by taking advantage of this natural geographic variation. Salt was iodized over a short period of time beginning in 1924. We use military data collected during WWI and WWII to compare outcomes of cohorts born before and after iodization in localities that were naturally poor and rich in iodine. We find that for the one quarter of the population most deficient in iodine this intervention raised IQ by approximately one standard deviation. Our results can explain roughly one decade's worth of the upward trend in IQ in the US (the Flynn Effect). We also document a large increase in thyroid-related deaths following the countrywide adoption of iodized salt, which affected mostly older individuals in localities with high prevalence of iodine deficiency.

SUBMITTER: Feyrer J

PROVIDER: S-EPMC6919660 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States.

Feyrer James J Politi Dimitra D Weil David N DN

Journal of the European Economic Association 20170408 2

Iodine deficiency is the leading cause of preventable mental retardation in the world today. The condition, which was common in the developed world until the introduction of iodized salt in the 1920s, is connected to low iodine levels in the soil and water. We examine the impact of salt iodization on cognitive outcomes in the US by taking advantage of this natural geographic variation. Salt was iodized over a short period of time beginning in 1924. We use military data collected during WWI and W ...[more]

PMID: 31853231

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Project description:Background: There has been tremendous progress over the past 25 years to control iodine deficiency disorders (IDDs) through universal salt iodization (USI). In 2019, using the median urinary iodine concentration (MUIC), only 19 countries in the world are classified as iodine deficient; in contrast in 1993, using the total goiter rate (TGR), 113 countries were classified as iodine deficient. However, few analyses have tried to quantify the global health and economic benefits of USI programs, and the shift from TGR to MUIC as the main indicator of IDDs complicates assessment of progress. Methods: We used a novel approach to estimate the impact of USI on IDDs, applying a regression model derived from observational data on the relationship between the TGR and the MUIC from 24 countries. The model was used to generate hypothetical national TGR values for 2019 based on current MUIC data. TGR in 1993 and modeled TGR in 2019 were then compared for 139 countries, and using consequence modeling, the potential health and economic benefits realized between 1993 and 2019 were estimated. Results: Based on this approach, the global prevalence of clinical IDDs (as assessed by the TGR) fell from 13.1% to 3.2%, and 720 million cases of clinical IDDs have been prevented by USI (a reduction of 75.9%). USI has significantly reduced the number of newborns affected by IDDs, with 20.5 million cases prevented annually. The resulting improvement in cognitive development and future earnings suggest a potential global economic benefit of nearly $33 billion. However, 4.8 million newborns will be affected by IDDs in 2019, who will experience life-long productivity losses totaling a net present value of $12.5 billion. Conclusions: The global improvements in iodine status over the past 25 years have resulted in major health and economic benefits, mainly in low- and middle-income countries. Efforts should now focus on sustaining this achievement and expanding USI to reach the continuing large number of infants who remain unprotected from IDDs.

Project description:The contribution of 100% fruit juice (FJ) to the total daily intakes of energy, sugars, and select vitamins and minerals and to the recommended dietary allowances (RDAs) or adequate intake (AI) of these micronutrients was assessed in individuals reporting the consumption of 100% FJ in the national dietary intake surveys of the United States (U.S.; n = 8661), the United Kingdom (UK; n = 2546) and Brazil (n = 34,003). Associations of 100% FJ intake with the odds of being overweight or obese also were assessed. Data from the U.S. National Health and Nutrition Examination Survey (2013-2014), the UK National Diet and Nutrition Survey (2012-2014), and Brazil's Pesquisa de Orçamentos Familiares (2008-2009) were used, and all analyses were limited to individuals reporting consumption of 100% FJ on at least one day of the dietary intake survey. Approximately 34%, 37%, and 42% of individuals surveyed reported the consumption of 100% FJ on at least one day of the dietary intake survey in the U.S., UK, and Brazil, respectively, and the average daily intakes of 100% FJ were 184 g, 130 g, and 249 g, respectively. Across the 3 countries, 100% FJ contributed to 3-6% of total energy intakes, 12-31% of total sugar intakes, 21-54% of total vitamin C intakes, 1-12% of total vitamin A intakes, 4-15% of total folate intakes, 7-17% of total potassium intakes, 2-7% of total calcium intakes, and 4-12% of total magnesium intakes. In a multivariate logistic regression model, juice intake was associated with a significant reduction in the odds of being overweight or obese in UK adults (OR = 0.79; 0.63, 0.99), and significant increases in the odds of being overweight or obese in UK children (OR = 1.16; 1.01, 1.33) and Brazilian adults (OR = 1.04; 1.00, 1.09). Nutrient contributions of 100% FJ vary according to regional intake levels. In all three countries studied, 100% FJ contributed to more than 5% of the RDAs for vitamin C and folate. In the U.S. and Brazil, 100% FJ contributed to more than 5% of the RDA for magnesium and more than 5% of the AI for potassium.

Project description:ObjectiveTo estimate the prevalence of use and the micronutrient contribution of dietary supplements among pregnant, lactating, and nonpregnant and nonlactating women in the United States.MethodsCross-sectional data from 1,314 pregnant, 297 lactating, and 8,096 nonpregnant and nonlactating women (aged 20-44 years) in the 1999-2014 National Health and Nutrition Examination Survey were combined to produce statistically reliable, nationally representative estimates. Information about dietary supplements used in the past 30 days was collected through an interviewer-administered questionnaire and in-home inventory. The prevalence of nutrient-specific supplement use, mean daily nutrient intakes from supplements among users, and motivations for supplement use were assessed. Differences by age, income, and trimester within pregnant women were also tested.ResultsSeventy-seven percent of pregnant women and 70% of lactating women used one or more dietary supplements, whereas 45% of nonpregnant and nonlactating women used supplements. In particular, 64% of pregnant and 54% of lactating women used prenatal supplements. Mean intakes of thiamin, riboflavin, niacin, folic acid, vitamins B6, B12, and C, iron, and zinc from supplements alone were at or above their respective recommended dietary allowances (RDAs) among pregnant and lactating supplement users. About half of pregnant and 40% of lactating women took supplements based on the recommendation of a health care provider. Among pregnant women, those in their first trimester, aged 20-34 years, or in a lower-income family were less likely to use supplements compared with their counterparts.ConclusionThe majority of pregnant and lactating women used dietary supplements, which contributed many nutrients in doses above the RDAs. Although inadequate Intakes of folate and iron are of concern among pregnant women who are not using supplements, supplement users often consumed high doses, suggesting a potential need of health care providers to discuss dietary supplement use and the recommended doses of nutrients during pregnancy and lactation.

Project description:BackgroundThe use of cognitive-enhancing medications and supplements among healthy adults continues to rise. Limited data exists on their use among resident physicians. Given their highly competitive and stressful lifestyle, we sought to evaluate the prevalence, motivations, and side effects of using cognitive-enhancing supplements and medications among resident physicians at a large United States academic institution.MethodsAn anonymous web-based survey was circulated to resident physicians inquiring about using cognitive-enhancing supplements and medications, as well as personal characteristics such as gender, marital and parental status, medical diagnoses, and medical specialty. Before circulation, we performed a pilot study. Weighted logistic regression analyses estimated the impact of personal characteristics on the probability of using both supplements and medications.ResultsSurvey response rate was 46.4%. Of respondents, 48.6% were female, 45.9% were married, 70.9% were without children, and 67.2% were in a non-surgical medical specialty. Few respondents had a related medical diagnosis, with attention deficit hyperactivity disorder being the most common (7.1%). Male, non-married, surgical residents were more likely to take supplements (odds ratio (OR) = 1.06, 1.05, and 1.05). Males, without children, and those who felt pressure to perform well, were afraid of being left behind, felt pressure because colleagues take them, or felt they could not reach their current level of training without medications were more likely to take medications (OR = 1.11, 1.04, 1.05, and 1.08). Adverse effects with medications were common.ConclusionSupplement and medication use for cognitive enhancement was high among resident physicians at a single institution despite few having a related medical diagnosis. This study raises awareness of the growing pressure in competitive residency environments to use cognitive enhancement regardless of the potential side effects.

Dataset Information

The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States.

Publications

The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States.

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