Current Estimates of Serum Vitamin C and Vitamin C Deficiency in the United States

Abstract

Objectives: This study aimed to assess current mean serum vitamin C level and prevalence of vitamin C deficiency (serum level <11.4 μmol/L) in the United States using nationally representative data, as well as compare to the previous decade's distributions. The study also explored the predictive effects of demographic variables on prevalence of vitamin C deficiency. Methods: The study population included 6740 non-institutionalized civilians aged 6 years and older in the National Health and Nutrition Examination Survey (NHANES) 2017-2018 who represented 274,157,096 individuals in the United States. Multivariable linear and logistic regression analyses were used to test the predictive effects of covariates. Serum vitamin C levels and deficiency prevalence were compared with NHANES 2005-2006 data using Student's t-tests. Results: The mean serum vitamin C level was 53.4 μmol/L (95% CI: 50.9, 55.8) and the prevalence of vitamin C deficiency was 5.9% (95% CI: 4.3, 7.6). In multivariable logistic regression analysis accounting for gender, age, race, smoking status, and obesity classification, only current smoking status was associated with deficiency (OR = 3.78 [95% CI: 2.70, 5.29], P = 0.02). Multivariable linear regression of the same factors found that underweight status (P = 0.04) and women (P = 0.02) were associated with higher vitamin C, while smoking status (P = 0.01) and obesity (P = 0.01) were associated with lower level. Although mean serum vitamin C declined from NHANES 2005-2006 to NHANES 2017-2018 (P < 0.05), there was no significant change in deficiency prevalence (P = 0.27). Conclusions: In NHANES 2017-2018, mean serum vitamin C level declined, but the prevalence of vitamin C deficiency did not significantly change from that during NHANES 2005-2006. Although gender, smoking status, and weight status were predictive of serum vitamin C level, deficiency was significantly more common only among smokers. These findings suggest that clinicians should continue to be wary of signs and symptoms of vitamin C deficiency and encourage vitamin supplementation when appropriate, particularly with patients who smoke.