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

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. 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. 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). 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. No funding was required/used for the research.