Vitamin C Status of US Adults Assessed as Part of the National Health and Nutrition Examination Survey Remained Unchanged between 2003-2006 and 2017-2018.

BACKGROUND: We compared serum vitamin C (VIC) status of the adult (≥20 y) US population in the National Health and Nutrition Examination Survey (NHANES) 2017-2018 with combined data from 2003-2004 and 2005-2006. METHODS: VIC was measured using HPLC with electrochemical detection. Mean data were stratified by age, sex, race/Hispanic origin, income, body mass index, dietary intake, supplement use, and smoking status. Prevalence of VIC deficiency (<11.4 µmol/L) was calculated. RESULTS: In NHANES 2017-2018, the mean VIC was 8 µmol/L higher in people ≥60 y compared with those 20-59 y of age, 10 µmol/L lower in men vs women, 8 µmol/L lower in low vs high income, 11 µmol/L lower in obese vs healthy weight, and 15 µmol/L lower in smokers vs nonsmokers. Differences in mean VIC across race/Hispanic origin groups ranged from 2 to 7 µmol/L. Mean VIC was 27 µmol/L higher with vitamin C-containing supplement use and positively associated (Spearman ρ = 0.33; P < 0.0001) with increasing dietary intake. The associations between mean VIC and the investigated covariates were generally consistent and the prevalence of deficiency was not significantly different between survey periods (6.8% vs 7.0%; P = 0.83). However, a few subgroups had double the risk. We found no significant survey differences in mean VIC (51.2 vs 54.0 µmol/L; P = 0.09). CONCLUSIONS: Overall VIC status of the US adult population has remained stable since last assessed in the NHANES 2005-2006 survey. Vitamin C deficiency remained high for those with low dietary intake and who smoke.

Fewer US adults had low or transitional vitamin B12 status based on the novel combined indicator of vitamin B12 status compared with individual, conventional markers, NHANES 1999-2004.

BACKGROUND: Elevated plasma methylmalonic acid (MMA) and/or total homocysteine (tHcy), as well as low serum vitamin B12 and/or holotranscobalamin (holoTC) are indicative of vitamin B12 deficiency. Combined indicators (cB12), which pool some or all 4 markers into an index, may be a more reliable diagnostic tool to overcome inconclusive diagnoses with individual markers. OBJECTIVES: We aimed to describe different cB12 score combinations and estimate the prevalence of low or transitional vitamin B12 status compared with individual markers. DESIGN: Using cross-sectional data for B12, MMA, and tHcy in persons ≥20 y participating in NHANES 1999-2004 (n = 12,335), we examined raw and covariate-adjusted regression models to assess determinants of 3cB12 (all 3 markers) and combinations of 2cB12 (2 markers). RESULTS: 3cB12 was significantly associated with B12 (Spearman r = 0.75), MMA (r = -0.70), and tHcy (r = -0.59). The 3cB12 reference interval (2.5th to 97.5th percentile) was -0.538 to 1.60. In covariate-adjusted models, we found no association of 3cB12 with age; adult females and users of B12 supplements had higher, while adults with advanced chronic kidney disease had lower 3cB12 levels regardless of race-Hispanic origin group (self-reported). Only 2.7% of adults had low or transitional vitamin B12 status using the proposed cB12 cutoff of ≤-0.5, while the prevalence of low (or low-normal) status depended on the selected individual marker and its cutoff: 2.2% and 13% for B12 < 148 and 148-222 pmol/L, respectively; 6.0% for MMA exceeding an age-specific cutoff (250-320 nmol/L); and 8.4% for tHcy > 13 µmol/L. The reference intervals for B12, MMA, and tHcy overlapped from the low (<-2.5) to the transitional (-2.5 to -0.5) and to the adequate (>-0.5) cB12 categories. CONCLUSIONS: Vitamin B12 deficiency may be overestimated among US adults when individual, conventional markers are used. When only 2 markers are available, the combination of B12 and MMA provides results comparable to 3cB12.

Supplemental Vitamin D Increased Serum Total 25-Hydroxyvitamin D in the US Adult Population During 2007-2014.

BACKGROUND: Data from the 2007-2010 NHANES suggested that vitamin D supplements contributed to increased serum concentrations of 25-hydroxyvitamin D [25(OH)D] in the US population. OBJECTIVES: We sought to determine whether 25(OH)D continued to increase during NHANES 2011-2014 and whether associations of 25(OH)D with preselected covariates differed across time periods. METHODS: For this study, 25(OH)D was measured in adults (≥20 y) using LC-MS/MS. Descriptive and regression analyses were stratified by survey period to investigate the effects of age, race-Hispanic origin, sex, season, BMI, dietary vitamin D, and vitamin D-containing supplements. A multiple linear regression model was used to assess 25(OH)D changes between two 4-y survey periods, namely 2007-2010 and 2011-2014. RESULTS: We observed several significant concomitant increases between 2007-2010 and 2011-2014: unadjusted mean 25(OH)D increased by 2.7 nmol/L (95% CI: 0, 5.4 nmol/L; P = 0.048), the percentage of persons taking any vitamin D-containing supplements increased 2.9% (95% CI: 0.03, 5.5%; P = 0.0314), and the percentage of persons taking high-dose (≥1000 IU/d) vitamin D-containing supplements increased 8.6% (95% CI: 6.9, 9.9%; P < 0.0001). With covariate adjustment, the increase in 25(OH)D from 2007-2010 to 2011-2014 was no longer statistically significant [1.4 nmol/L (95% CI: -3.0, 0.23 nmol/L; P = 0.09)]. After adjustments, several large differences in 25(OH)D remained, namely non-Hispanic blacks had 25(OH)D 22 nmol/L lower than that of non-Hispanic whites, and users of vitamin D-containing supplements ≥1000 IU/d had 25(OH)D 31 nmol/L higher than that of nonusers. CONCLUSIONS: After adjusting for vitamin D supplement dose, the overall adjusted increase in 25(OH)D was no longer statistically significant, suggesting that changes in US adults' 25(OH)D concentrations between NHANES periods 2007-2010 and 2011-2014 may primarily be associated with changes in vitamin D supplementation.

Demographic, Physiologic, and Lifestyle Characteristics Observed with Serum Total Folate Differ Among Folate Forms: Cross-Sectional Data from Fasting Samples in the NHANES 2011-2016.

BACKGROUND: Serum folate forms were measured in the US population during recent NHANES to assess folate status. OBJECTIVE: We describe post-folic acid-fortification concentrations of serum folate forms in the fasting US population ≥1 y from the NHANES 2011-2016. METHODS: We measured 5 biologically active folates and 1 oxidation product (MeFox) of 5-methyltetrahydrofolate (5-methyl-THF). We calculated geometric means of 5-methyl-THF, unmetabolized folic acid (UMFA), nonmethyl folate (sum of tetrahydrofolate, 5-formyltetrahydrofolate, and 5,10-methenyltetrahydrofolate), total folate (sum of above biomarkers), and MeFox by demographic, physiologic, and lifestyle variables; estimated the magnitude of variables on biomarker concentrations after covariate adjustment; and determined the prevalence of UMFA >2 nmol/L. RESULTS: After demographic adjustment, age, sex, and race-Hispanic origin were significantly associated with most folate forms. MeFox increased with age, while 5-methyl-THF, UMFA, and nonmethyl folate displayed U-shaped age patterns. Compared with non-Hispanic whites, non-Hispanic blacks had 23% lower predicted 5-methyl-THF but comparable UMFA; non-Hispanic Asians had comparable 5-methyl-THF but 28% lower UMFA; Hispanics, non-Hispanic Asians, and non-Hispanic blacks had ∼20% lower MeFox. After additional physiologic and lifestyle adjustment, predicted UMFA and MeFox concentrations were 43% and 112% higher, respectively, in adults with chronic kidney disease and 17% and 15% lower, respectively, in adults consuming daily 1-<2 alcoholic beverages; 5-methyl-THF concentrations were 20% lower in adult smokers. The prevalence of UMFA >2 nmol/L was highest in persons aged ≥70 y (9.01%) and lowest in those aged 12-19 y (1.14%). During 2011-2014, the prevalence was 10.6% in users and 2.22% in nonusers of folic acid-containing supplements. CONCLUSIONS: In fasting persons ≥1 y, the demographic, physiologic, and lifestyle characteristics observed with serum total folate differed among folate forms, suggesting biological and/or genetic influences on folate metabolism. High UMFA was mostly observed in supplement users and older persons.

Folate status in the US population 20 y after the introduction of folic acid fortification.

BACKGROUND: Enriched cereal-grain products have been fortified in the United States for >20 y to improve folate status in women of reproductive age and reduce the risk of folic acid-responsive neural tube birth defects (NTDs). OBJECTIVES: Our objectives were to assess postfortification changes in folate status in the overall US population and in women aged 12-49 y and to characterize recent folate status by demographic group and use of folic acid-containing supplements. METHODS: We examined cross-sectional serum and RBC folate data from the NHANES 1999-2016. RESULTS: Serum folate geometric means increased from 2007-2010 to 2011-2016 in persons aged ≥1 y (38.7 compared with 40.6 nmol/L) and in women (35.3 compared with 37.0 nmol/L), whereas RBC folate showed no significant change. Younger age groups, men, and Hispanic persons showed increased serum and RBC folate concentrations, whereas non-Hispanic black persons and supplement nonusers showed increased serum folate concentrations. The folate insufficiency prevalence (RBC folate <748 nmol/L; NTD risk) in women decreased from 2007-2010 (23.2%) to 2011-2016 (18.6%) overall and in some subgroups (e.g., women aged 20-39 y, Hispanic and non-Hispanic black women, and supplement nonusers). After covariate adjustment, RBC folate was significantly lower in all age groups (by ∼10-20%) compared with persons aged ≥60 y and in Hispanic (by 8.2%), non-Hispanic Asian (by 12.1%), and non-Hispanic black (by 20.5%) compared with non-Hispanic white women (2011-2016). The 90th percentile for serum (∼70 nmol/L) and RBC (∼1800 nmol/L) folate in supplement nonusers aged ≥60 y was similar to the geometric mean in users (2011-2014). CONCLUSIONS: Blood folate concentrations in the US population overall and in women have not decreased recently, and folate insufficiency rates are ∼20%. Continued monitoring of all age groups is advisable given the high folate status particularly in older supplement users.

Vitamin D status in the United States, 2011-2014.

BACKGROUND: Vitamin D is important for bone health; in 2014 it was the fifth most commonly ordered laboratory test among Medicare Part B payments. OBJECTIVES: The aim of this study was to describe vitamin D status in the US population in 2011-2014 and trends from 2003 to 2014. METHODS: We used serum 25-hydroxyvitamin D data from NHANES 2011-2014 (n = 16,180), and estimated the prevalence at risk of deficiency (<30 nmol/L) or prevalence at risk of inadequacy (30-49 nmol/L) by age, sex, race and Hispanic origin, and dietary intake of vitamin D. We also present trends between 2003 and 2014. RESULTS: In 2011-2014, the percentage aged ≥1 y at risk of vitamin D deficiency or inadequacy was 5.0% (95% CI: 4.1%, 6.2%) and 18.3% (95% CI: 16.2%, 20.6%). The prevalence of at risk of deficiency was lowest among children aged 1-5 y (0.5%; 95% CI: 0.3%, 1.1%), peaked among adults aged 20-39 y (7.6%; 95% CI: 6.0%, 9.6%), and fell to 2.9% (95% CI: 2.0%, 4.0%) among adults aged ≥60 y; the prevalence of at risk of inadequacy was similar. The prevalence of at risk of deficiency was higher among non-Hispanic black (17.5%; 95% CI: 15.2%, 20.0%) than among non-Hispanic Asian (7.6%; 95% CI: 5.9%, 9.9%), non-Hispanic white (2.1%; 95% CI: 1.5%, 2.7%), and Hispanic (5.9%; 95% CI: 4.4%, 7.8%) persons; the prevalence of at risk of inadequacy was similar. Persons with higher vitamin D dietary intake or who used supplements had lower prevalences of at risk of deficiency or inadequacy. From 2003 to 2014 there was no change in the risk of vitamin D deficiency; the risk of inadequacy declined from 21.0% (95% CI: 17.9%, 24.5%) to 17.7% (95% CI: 16.0%, 19.7%). CONCLUSION: The prevalence of at risk of vitamin D deficiency in the United States remained stable from 2003 to 2014; at risk of inadequacy declined. Differences in vitamin D status by race and Hispanic origin warrant additional investigation.