The effect of vitamin D on insulin resistance index and fasting blood glocuse in pregnant women: A Randomized Controlled Clinical Trial

Abstract

Abstract Background: Pregnancy changes affect glucose metabolism and insulin sensitivity, and increase insulin production by the pancreas. If this disorder of blood glucose regulation occurs for the first time during pregnancy, it is called gestational diabetes. This disorder is increasing worldwide and is one of the most common metabolic disorders during pregnancy. Vitamin D, now known as prohormone, has a function beyond regulating calcium and magnesium metabolism and may play a role in the health of other tissues, including the regulation of blood sugar. This is due to the effect of vitamin D on pancreatic beta cell function. Therefore, the purpose of the present study was to determine the effect of vitamin D on insulin resistance index (HOMA-IR) and fasting blood glucose (FBS) (primary outcomes), depression symptoms, gestational diabetes frequency, abortion frequency and side effects (secondary outcomes) in pregnant women. Methods: This randomized controlled clinical trial was performed on 88 healthy pregnant women with 8 to 10 weeks of pregnancy. From the participants, a blood sample was taken to determine the level of vitamin D. After receiving the result, if the serum level of vitamin D was below 30 ng/ml, the written and informed consent form was completed by pregnant women and research questionnaires including demographic-social information and depression were completed by interview with the researcher. Fasting frozen blood samples were used to determine FBS before intervention for participants. Participants were randomly divided into two groups: intervention group (n=44; receiving 4000 units of oral vitamin D daily) and control group (n=44; receiving placebo with the same protocol). The intervention lasted for 18 weeks and after the intervention at the 26th week of pregnancy, blood samples were taken again to check HOMA-IR (Homeostatic Model Assessment of Insulin Resistance), FBS (Fasting Blood Sugar), FBI (Fasting Blood Insulin) and vitamin D levels, from both intervention and control groups in fasting state. One hour and two hours after the first blood sample, two more samples were taken to check 1h-glucose and 2h-glucose and the depression questionnaire was completed again. Data were analyzed using independent t-test, Mann-Whitney U, ANCOVA and chi-square. Results: After the intervention, there was no statistically significant difference between the two groups in terms of FBS (P = 0.850), FBI (P = 0.353), HOMA-IR (P = 0.632), mean score of depressive symptoms (P = 0.505), frequency of gestational diabetes (P = 0.187) and frequency of abortion (P = 1.000) but there was statistically significant difference in terms of serum vitamin D level (P = 0.016) and musculoskeletal pain including knee pain (P = 0.025), ankle pain (P <0.001) and leg pain (P <0.001). In vitamin D group, one participant reports nausea and one reports constipation. In placebo group, two participants report nausea, one reports headache and three report constipation. Conclusion: Vitamin D could improve the musculoskeletal pain in pregnant women but couldn`t decrease FBS, FBI, HOMA-IR, depression symptoms score, incidence of GDM and abortion.