Association between total vitamin C intake and hypothyroidism among Hashimoto thyroiditis: National Health and Nutrition Examination Survey, 2007-2012.

Oxidative stress may be involved in the progression of hypothyroidism in patients with Hashimoto thyroiditis (HT). Vitamin C is a well-known powerful antioxidant. To our knowledge, whether vitamin C intake relates to hypothyroidism in patients with HT remains unclear. In this cross-sectional study based on the National Health and Nutrition Examination Survey, 2007-2012, we aimed to explore the relationship between total vitamin C intake and hypothyroidism in patients with HT, using multivariate logistic regression models and restricted cubic spline analyses. Our results showed a significant negative linear association between total vitamin C intake (log10-transformed data) and hypothyroidism in HT. Compared with those with the lowest quartile of total vitamin C intake (log10-transformed), participants with the highest quartile were at lower odds of having hypothyroidism (adjusted OR 0·40, 95 % CI: 0·18, 0·88, P_trend = 0·027). This association was consistent in subgroups stratified by sex (P_{for interaction} = 0·084) and age (≥ 60 years and < 60 years, P_{for interaction} = 0·330). This study revealed that total vitamin C intake was inversely associated with hypothyroidism among individuals with HT, indicating that higher vitamin C intakes (4·57-1258·9 mg/d) may be associated with a lower likelihood of hypothyroidism among HT participants.