In terms of dosage, the researchers found that 200 mg per day of dietary vitamin C may help reduce the odds of gestational diabetes mellitus—a degree of intolerance to glucose that sometimes occurs during pregnancy.

The effects were consistent even after controlling for confounding variables such as body mass index, age, supplements use, energy intake, family history of diabetes, as well as vitamins A and E intake.

Important to note, the researchers added, was that there was no association between total amount of vitamin C intake with gestational diabetes mellitus risk.

“The main reason is that the intake of total vitamin C includes vitamin C from supplements, mostly multivitamin containing vitamin C,”​ they wrote in their report, published​​ in the February issue of the journal Clinical Nutrition.​

The study’s participants were part of a cohort of 3009 Chinese women enrolled in the ongoing Tongji Maternal and Child Health study. Of these women, 344, or 11.4%, were diagnosed with gestational diabetes mellitus.

They extrapolated information of vitamin C intake as well as supplement use from questionnaires.

The role of vitamin C supplements?​

Less than half, or 45% of the total cohort, reported taking vitamin C supplements. Of this number, almost all (99.64%) reported that the vitamin C supplement was part of a multivitamin blend.

"Participants who used vitamin C supplements were more likely to have insufficient dietary vitamin C intake,” ​the researchers reported. Instead, pregnant women that ate more fruits and vegetables tended to have a higher dietary intake of vitamin C.

They pointed to a 2011 study​​ on US adults by Harvard Medical School researchers which posited that, while multivitamin use was not associated with diabetes risk, pure vitamin C supplements may reduce the risk of diabetes.

“Whether pure vitamin C supplements has an effect on gestational diabetes mellitus risk needs further research,”​ the Chinese researchers wrote in their report.