"Although the precise pathogenesis of diabetes is not well-understood, in vitro and in vivo studies, and clinical evidence, have demonstrated a link between [gestational diabetes] and oxidative stress," Nianhong Yang, PhD, a professor and director of the department of nutrition and food hygiene at Tongji Medical College, Huazhong University of Science and Technology in Hubei, China, and colleagues wrote. "Observational studies have reported that women with [gestational diabetes] exhibited elevated biomarkers of oxidative stress, including DNA damage markers and lipid peroxidation products. It is possible that dietary antioxidants may play a role in lowing [gestational diabetes] risk."

Yang and colleagues analyzed data from 3,009 pregnant women (mean age, 28.1 years) in Wuhan, China, from the Tongji Maternal and Child Health Cohort. Each participant underwent a prenatal visit before the 16th week of gestation between January 2013 and May 2016.

Participants provided demographic and lifestyle data via a structured questionnaire; vitamin C supplement intake and dietary behavior were assessed via in-person interviews. For dietary behavior, participants detailed their normal diet during the previous 4 weeks. The researchers defined dietary vitamin C intake into three groups: inadequate (< 115 mg per day), adequate (115 mg per day to 200 mg per day) and above adequate ( 200 mg per day). Participants also underwent a 75-g 2-hour oral glucose tolerance test from week 24 to week 32 of pregnancy.

During the study, 344 women developed gestational diabetes, and the mean dietary vitamin C intake of all participants was 163.53 mg per day. The researchers reported that 744 of the participants had inadequate dietary vitamin C intake compared with 1,532 participants with adequate intake and 733 with above adequate intake. The primary source of dietary vitamin C consumption was leafy green vegetables, cabbage and chili, along with other fruits and vegetables.

Participants with above adequate dietary vitamin C intake were less likely to develop gestational diabetes (OR = 0.74; 95% CI, 0.55-0.99) compared with participants with adequate intake, which was used as reference, and inadequate (OR = 1.09; 95% CI, 0.83-1.41) intake, which supported the researchers' finding that dietary C intake had a negative association with gestational diabetes.

Conversely, no significant association was found between total vitamin C intake, which combined dietary and supplement sources, and the risk for gestational diabetes (OR = 1.04; 95% CI, 0.71-1.53). The researchers noted that this could be because average dietary vitamin C intake was lower for participants who took vitamin C supplements (156.3 mg per day) compared with those who did not (165.2 mg per day) and bioavailability from supplements is lower than that from food sources. - by Phil Neuffer