Chia-Yih Wang

Predicted contribution of folic acid fortification of corn masa flour to the usual folic acid intake for the US population: National Health and Nutrition Examination Survey 2001–2004

BACKGROUND Folic acid can prevent up to 70% of neural tube defects (NTDs) if taken before pregnancy. Compared with other race-ethnicities, Hispanic women have higher rates of NTDs, lower rates of folic acid supplement use, and lower total folic acid intakes. OBJECTIVE The objective was to assess potential effects of fortifying corn masa flour with folic acid on Mexican American women and other segments of the US population. DESIGN A model was developed by using data from the National Health and Nutrition Examination Survey 2001-2004 to estimate the folic acid content in foods containing corn masa flour if fortified at a level of 140 microg folic acid/100 g corn masa flour. RESULTS Had corn masa flour fortification occurred, we estimated that Mexican American women aged 15-44 y could have increased their total usual daily folic acid intake by 19.9% and non-Hispanic white women by 4.2%. Among the US population, estimated relative percentage increases in total usual daily folic acid intake with corn masa flour fortification were greatest among Mexican Americans (16.8%) and lowest among children aged 1-3 y (2%) and adults aged >51 y (0-0.5%). CONCLUSION Analyses suggest that corn masa flour fortification would have effectively targeted Mexican Americans, specifically, Mexican American women, without substantially increasing folic acid intake among other segments of the population. Such increases could reduce the disparity in total folic acid intake between Mexican American and non-Hispanic white women of childbearing age and implies that an additional NTD preventive benefit would be observed for Mexican American women.

Comparison of population iodine estimates from 24-hour urine and timed-spot urine samples.

BACKGROUND Median urine iodine concentration (UIC; μg/L) in spot urine samples is recommended for monitoring population iodine status. Other common measures are iodine:creatinine ratio (I/Cr; μg/g) and estimated 24-hour urine iodine excretion (UIE; I/Cr × predicted 24-hour Cr; μg/day). Despite different units, these measures are often used interchangeably, and it is unclear how they compare with the reference standard 24-hour UIE. METHODS Volunteers aged 18-39 years collected all their urine samples for 24 hours (n=400). Voids from morning, afternoon, evening, overnight, and a composite 24-hour sample were analyzed for iodine. We calculated median observed 24-hour UIE and 24-hour UIC, and spot UIC, I/Cr, and two measures of estimated UIE calculated using predicted 24-hour Cr from published estimates by Kesteloot and Joosens (varies by age and sex) and published equations by Mage et al. (varies by age, sex, race, and anthropometric measures). We examined mean differences and relative difference across iodine excretion levels using Bland-Altman plots. RESULTS Median 24-hour UIE was 173.6 μg/day and 24-hour UIC was 144.8 μg/L. From timed-spot urine samples, estimates were: UIC 147.3-156.2 μg/L; I/Cr 103.6-114.3 μg/g, estimated 24-hour UIE (Kesteloot and Joosens) 145.7-163.3 μg/day; and estimated 24-hour UIE (Mage) 176.5-187.7 μg/day. Iodine measures did not vary consistently by timing of spot urine collection. Compared with observed 24-hour UIE, on average, estimated (Mage) 24-hour UIE was not significantly different, while estimated 24-hour UIE (Kesteloot and Joosens) was significantly different for some ethnicity/sex groups. Compared with 24-hour UIC, on average, spot UIC did not differ. CONCLUSIONS Estimates of UIC, I/Cr, and estimated 24-hour UIE (I/Cr × predicted 24-hour Cr) from spot urine samples should not be used interchangeably. Estimated 24-hour UIE, where predicted 24-hour Cr varies by age, sex, ethnicity, and anthropometric measures and was calculated with prediction equations using data from the sample, was more comparable to observed 24-hour UIE than when predicted 24-hour Cr was from published estimates from a different population. However, currently no cutoffs exist to interpret population estimated 24-hour UIE values.

Difference between 24-h diet recall and urine excretion for assessing population sodium and potassium intake in adults aged 18–39 y

BACKGROUND Limited data are available on the accuracy of 24-h dietary recalls used to monitor US sodium and potassium intakes. OBJECTIVE We examined the difference in usual sodium and potassium intakes estimated from 24-h dietary recalls and urine collections. DESIGN We used data from a cross-sectional study in 402 participants aged 18-39 y (∼50% African American) in the Washington, DC, metropolitan area in 2011. We estimated means and percentiles of usual intakes of daily dietary sodium (dNa) and potassium (dK) and 24-h urine excretion of sodium (uNa) and potassium (uK). We examined Spearmans correlations and differences between estimates from dietary and urine measures. Multiple linear regressions were used to evaluate the factors associated with the difference between dietary and urine measures. RESULTS Mean differences between diet and urine estimates were higher in men [dNa - uNa (95% CI) = 936.8 (787.1, 1086.5) mg/d and dK - uK = 571.3 (448.3, 694.3) mg/d] than in women [dNa - uNa (95% CI) = 108.3 (11.1, 205.4) mg/d and dK - uK = 163.4 (85.3, 241.5 mg/d)]. Percentile distributions of diet and urine estimates for sodium and potassium differed for men. Spearmans correlations between measures were 0.16 for men and 0.25 for women for sodium and 0.39 for men and 0.29 for women for potassium. Urinary creatinine, total caloric intake, and percentages of nutrient intake from mixed dishes were independently and consistently associated with the differences between diet and urine estimates of sodium and potassium intake. For men, body mass index was also associated. Race was associated with differences in estimates of potassium intake. CONCLUSIONS Low correlations and differences between dietary and urinary sodium or potassium may be due to measurement error in one or both estimates. Future analyses using these methods to assess sodium and potassium intake in relation to health outcomes may consider stratifying by factors associated with the differences in estimates from these methods. This trial was registered at clinicaltrials.gov as NCT01631240.

Awareness of Federal Dietary Guidance in Persons Aged 16 Years and Older: Results from the National Health and Nutrition Examination Survey 2005-2006

The National Health and Nutrition Examination Survey 2005-2006 included questions on awareness of the Dietary Guidelines for Americans (DGA), the Food Guide Pyramid, and the 5 A Day for Better Health Program. Prevalence of awareness of federal dietary guidance was estimated and differences were tested across demographic traits, health characteristics, and diet-related attitudes and behavior. The continuous National Health and Nutrition Examination Survey uses a nationally representative cross-sectional sample design. The analytic sample consisted of 5,499 persons aged 16 years and older with complete data. Among persons aged 16 years and older, 83.8% had heard of at least one of the initiatives: 49.2% had heard of the DGA, 80.6% had heard of the Food Guide Pyramid, and 51.2% had heard of the 5 A Day program. There was a linear trend of decreasing awareness of at least one of the guidance efforts with increasing age. Differences by sex, race/ethnicity, education, and income were also observed. Differences by body mass index were not statistically significant; however, significant differences were seen with fatalistic beliefs about body weight. Differences by smoking, self-assessed diet quality, and eating out frequency were not statistically significant after adjustment for sex, age, race/ethnicity, education, and income. These results may be useful in promotion of the upcoming edition of the DGA and to suggest population groups that may benefit from strengthened and more innovative education efforts at the public health program level and at the clinic level.

Association Between Urinary Sodium and Potassium Excretion and Blood Pressure Among Adults in the United States: National Health and Nutrition Examination Survey, 2014.

Background: Higher levels of sodium and lower levels of potassium intake are associated with higher blood pressure. However, the shape and magnitude of these associations can vary by study participant characteristics or intake assessment method. Twenty-four–hour urinary excretion of sodium and potassium are unaffected by recall errors and represent all sources of intake, and were collected for the first time in a nationally representative US survey. Our objective was to assess the associations of blood pressure and hypertension with 24-hour urinary excretion of sodium and potassium among US adults. Methods: Cross-sectional data were obtained from 766 participants age 20 to 69 years with complete blood pressure and 24-hour urine collections in the 2014 National Health and Nutrition Examination Survey, a nationally representative survey of the US noninstitutionalized population. Usual 24-hour urinary electrolyte excretion (sodium, potassium, and their ratio) was estimated from ⩽2 collections on nonconsecutive days, adjusting for day-to-day variability in excretion. Outcomes included systolic and diastolic blood pressure from the average of 3 measures and hypertension status, based on average blood pressure ≥140/90 and antihypertensive medication use. Results: After multivariable adjustment, each 1000-mg difference in usual 24-hour sodium excretion was directly associated with systolic (4.58 mm Hg; 95% confidence interval [CI], 2.64–6.51) and diastolic (2.25 mm Hg; 95% CI, 0.83–3.67) blood pressures. Each 1000-mg difference in potassium excretion was inversely associated with systolic blood pressure (–3.72 mm Hg; 95% CI, –6.01 to –1.42). Each 0.5 U difference in sodium-to-potassium ratio was directly associated with systolic blood pressure (1.72 mm Hg; 95% CI, 0.76–2.68). Hypertension was linearly associated with progressively higher sodium and lower potassium excretion; in comparison with the lowest quartile of excretion, the adjusted odds of hypertension for the highest quartile was 4.22 (95% CI, 1.36–13.15) for sodium, and 0.38 (95% CI, 0.17–0.87) for potassium (P<0.01 for trends). Conclusions: These cross-sectional results show a strong dose-response association between urinary sodium excretion and blood pressure, and an inverse association between urinary potassium excretion and blood pressure, in a nationally representative sample of US adults.

Assessing U.S. Sodium Intake through Dietary Data and Urine Biomarkers

Sodium intake is related to blood pressure, an established risk factor for heart disease and stroke. Reducing intake may save billions in United States health care dollars annually. Efforts targeting sodium reductions make accurate monitoring vital, yet limited information exists on the accuracy of the current data to assess sodium intake in the United States population. In this symposium, new findings were presented on the accuracy of estimating population 24-h urinary excretion of sodium from spot urine specimens or sodium intake from 24-h dietary recalls. Differences in accuracy by sex, BMI, and race were apparent as well as by timing of spot urine collections. Although some published equations appear promising for estimating group means, others are biased. Individual estimates of sodium intake were highly variable and adjustment for within-individual variation in intake is required for estimating population prevalence or percentiles. Estimates indicated United States sodium intake remains high.

Validity of predictive equations for 24-h urinary potassium excretion based on timing of spot urine collection among adults: the MESA and CARDIA Urinary Sodium Study and NHANES Urinary Sodium Calibration Study

Background 24-h urine collections are the suggested method to measure daily urinary potassium excretion (uK) but are costly and burdensome to implement. Objective This study tested how well existing equations with the use of spot urine samples can estimate 24-h uK and if accuracy varies by timing of spot urine collection, age, race, or sex. Design This cross-sectional study used data from 407 participants aged 18-39 y from the Washington, DC area in 2011 and 554 participants aged 45-79 y from Chicago in 2013. Spot urine samples were collected in individual containers for 24 h, and 1 for each timed period (morning, afternoon, evening, and overnight) was selected. For each selected timed spot urine, 24-h uK was predicted through the use of published equations. Difference (bias) between predicted and measured 24-h uK was calculated for each timed period and within age, race, and sex subgroups. Individual-level differences were assessed through the use of Bland-Altman plots and correlation tests. Results For all equations, regardless of the timing of spot urine, mean bias was usually significantly different than 0. No one prediction equation was unbiased across all sex, race, and age subgroups. With the use of the Kawasaki and Tanaka equations, 24-h uK was overestimated at low levels and underestimated at high levels, whereas observed differential bias with the Mage equation was in the opposite direction. Depending on prediction equation and timing of urine sample, 61-75% of individual 24-h uKs were misclassified among 500-mg incremental categories from <1500 to ≥3000 mg. Correlations between predicted and measured 24-h uK were poor to moderate (0.19-0.71). Conclusion Because predicted 24-h uK accuracy varies by timing of spot urine collection, published prediction equations, and within age-race-sex subgroups, study results making use of predicted 24-h uK in association with health outcomes should be interpreted with caution. It is possible that a more accurate prediction equation can be developed leading to different results.