Vitamin D in gestational diabetes mellitus and its association with hyperglycaemia, insulin sensitivity and other factors

We investigated if vitamin D is independently associated with hyperglycaemia in gestational diabetes mellitus (GDM). Serum 25 hydroxy vitamin D (25OHD), fasting blood glucose (FBG), HbA1c, fructosamine, insulin sensitivity (QUICKI equation), body mass index, clothing style and outdoor activity were measured in 58 pregnant women with GDM during the third trimester. 25OHD was also measured in 20 women with normal pregnancies. There was no significant difference in mean 25OHD concentrations between GDM (14.43 ± 5.27 ng/ml) and normal (15.45 ± 5.29 ng/ml) pregnancies, p = .354. However, a higher percentage of GDM subjects had 25OHD concentration <19.8 ng/ml (86 versus 65%, p = .003). 25OHD did not correlate with FBG, HbA1c, fructosamine, insulin sensitivity or insulin dosage (p > .05). On multivariate analysis, only ethnicity (p = .006) and outdoor activity (p = .004) were associated with 25OHD. We conclude that the lower 25OHD levels in our GDM patients were related to ethnicity and outdoor activity (Study FF-2017-111, National University of Malaysia, 16 March 2017).IMPACT STATEMENTWhat is already known on this subject? Vitamin D deficiency in pregnancy is widespread and particularly in certain ethnic groups. Low vitamin D levels may be an aetiological factor for gestational diabetes mellitus (GDM) but previous studies provide conflicting results perhaps due to confounding factors.What do the results of this study add? In this study of pregnant women with GDM from different ethnic backgrounds, we analysed serum 25-hydroxy vitamin D (25OHD) levels together with other confounding factors, that is, body mass index, ethnicity and sunlight exposure. Furthermore, instead of using consensus values, we determined cut-offs for different vitamin D status from normal pregnancies matched for gestational age and ethnicity. We found that a higher percentage of GDM subjects had lower vitamin D status but there was no correlation with hyperglycaemia or insulin sensitivity. The study showed that lower vitamin D levels in GDM was associated with ethnicity and less outdoor activity.What the implications are of these findings for clinical practice and/or further research? In GDM patients, low vitamin D levels may be modifiable by supplementation or lifestyle change. Longitudinal studies are needed to determine whether this would impact on the occurrence of GDM.