Vitamin D levels important in gestational diabetes

An Australian study has found that low vitamin D levels are linked with poorer blood glucose control in women with gestational diabetes (diabetes in pregnancy).

Researchers from Westmead Hospital in Sydney studied almost 150 women attending the gestational diabetes (GDM) clinic at Westmead Hospital from February 2007 to February 2008, who were on average around 35 weeks of pregnancy. They had blood tests during the third trimester of pregnancy to measure HbA1c (which reflects average blood glucose control over the previous 2-3 months) and vitamin D levels. GDM was diagnosed using an oral glucose tolerance test (OGTT).

They found that that 41% of the women had low levels of vitamin D (50nmol/L or below). Lower levels were seen in women from Middle Eastern and Indian backgrounds, as well as women who performed home duties compared to those in paid employment. Not surprisingly, vitamin D levels were much higher in summer than during other seasons.

Women with lower vitamin D levels were found to have higher blood glucose levels – both fasting and 2 hour glucose levels during the oral glucose tolerance test, and HbA1c levels. Low vitamin D levels were associated with a higher HbA1c, independent of other factors.

The authors suggest randomised trials are needed to determine whether vitamin D plays a role in blood glucose control in gestational diabetes. In the meantime, considering the high prevalence of vitamin D deficiency they found in the study, and the fact that low vitamin D levels in pregnancy can have other adverse effects for the unborn baby, they recommend routine testing of vitamin D for all pregnant women, either alongside or prior to screening for GDM.

Lau et al. Serum 25-hydroxyvitamin D and glycated haemoglobin levels in women with gestational diabetes mellitus. Med J Aust. 2011 Apr 4;194(7):334-7.

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