Vitamin D and gestational diabetes mellitus: a systematic review based on data free of Hawthorne effect

The Role of Vitamin D in the Development of Diabetes Post Gestational Diabetes Mellitus: A Systematic Literature Review

Women diagnosed with gestational diabetes mellitus (GDM) are more likely to later develop diabetes. Evidence from some previous reviews suggests that low vitamin D status during pregnancy increases the risk of developing GDM, but whether vitamin D during pregnancy also influences the risk of diabetes post GDM is less well studied. Thus, the aim of this systematic literature review was to summarize the current available literature on that topic. This review considered observational studies and randomized controlled trials (RCTs). Five databases were searched. The risk of bias of the included studies was assessed. A total of six studies were included: three observational studies and three RCTs. Findings were inconsistent across the six included studies. However, when considering RCTs only, the findings more strongly suggested that vitamin D supplementation during and after pregnancy did not have an influence on markers of diabetes development or diabetes development post GDM. This systematic review highlights inconsistent findings on the associations between vitamin D supplementation or concentration during and after pregnancy and markers of diabetes development or diabetes development post GDM; and although results from randomized interventional studies more strongly suggested no associations, the conclusion holds a high degree of uncertainty.

Relationship between vitamin D status in the first trimester of pregnancy and gestational diabetes mellitus - A nested case-control study

BACKGROUND & AIMS

Gestational diabetes mellitus (GDM) is one of the most frequent medical complications during pregnancy. It has been associated with many adverse pregnancy, fetal and neonatal outcomes, as well as with an increased risk for mothers and children in the long term. There is a growing interest in vitamin D and its potential role in the development of metabolic disorders. However, the medical literature is not consensual. The aim of this study was to assess the risk of GDM according to vitamin D status during the first trimester.

METHODS

This study is a nested case-control study performed from a multicenter prospective observational cohort of pregnant women assessed for 25-hydroxyvitamin D levels (25OHD). Three hundred ninety-three patients were included in the initial cohort. After applying exclusion criteria, a total of 1191 pregnant women were included. Two hundred fifty women with GDM (cases) were matched to 941 women without GDM (controls) for parity, age, body mass index before pregnancy, the season of conception, and phototype. This study was funded by a grant from the "Programme Hospitalier de Recherche Publique 2010".

RESULTS

The GDM risk was significantly greater for patients with 25OHD levels <20 ng/mL (OR = 1∙42, 95% CI 1∙06-1∙91; p = 0∙021). However, there was no significant relationship with other thresholds. The study of 25OHD levels with the more precise cutting of 5 units intervals showed a variable relationship with GDM risk, as the risk was low for very low 25OHD levels, increased for moderated levels, decreased for normal levels, and finally increased for higher levels.

CONCLUSION

According to our study, there seems to be no linear relationship between GDM and 25OHD levels in the first trimester of pregnancy since GDM risk does not continuously decrease as 25OHD concentrations increase. Our results most probably highlight the absence of an association between 25OHD levels and GDM risk.

Targeted 25-hydroxyvitamin D concentration measurements and vitamin D3 supplementation can have important patient and public health benefits

Over the past two decades, many studies reported the benefits of higher 25-hydroxyvitamin D [25(OH)D] concentrations for nonskeletal effects. Researchers found significant benefits in reducing risk of acute respiratory tract infections, many types of cancer, type 2 diabetes mellitus, premature death, and adverse pregnancy and birth outcomes. In addition, 25(OH)D concentrations are low for various reasons in several categories of people, including the obese, those with dark skin living at higher latitudes, the elderly, and those who do not eat much eggs, fish, meat, or vitamin D fortified milk. Measuring 25(OH)D concentrations is one way to both increase the awareness of vitamin D's importance in maintaining good health and to encourage vitamin D supplementation or increased solar ultraviolet-B exposure to sustain well-being throughout life by reducing disease incidence. Although 20 ng/ml seems adequate to reduce risk of skeletal problems and acute respiratory tract infections, concentrations above 30 ng/ml have been associated with reduced risk of cancer, type 2 diabetes mellitus, and adverse pregnancy and birth outcomes. Thus, judicious testing of 25(OH)D concentrations could reduce disease incidence and make treatment expenditures more cost-effective.

Effects of Nutritional Strategies on Glucose Homeostasis in Gestational Diabetes Mellitus: A Systematic Review and Network Meta-Analysis

BACKGROUND

Gestational diabetes mellitus (GDM) is one of the most common complications of pregnancy, and nutritional therapy is the basis of GDM treatment. However, the effects of different forms of nutritional supplementation on improving gestational diabetes are uncertain.

OBJECTIVE

We conducted a network meta-analysis to evaluate the effects of supplementation with different nutrients on glucose metabolism in women with GDM.

METHODS

We conducted a literature search using PubMed, EMBASE, and the Cochrane Library to identify randomized controlled trials (RCTs) comparing the differences between different nutritional strategies in women with GDM. The Cochrane tool was used to assess the risk of bias. Pairwise meta-analysis and network meta-analysis were used to compare and rank the effects of nutritional strategies for the improvement of fasting plasma glucose (FPG), serum insulin, and homeostasis model assessment-insulin resistance (HOMA-IR).

RESULTS

We included thirteen RCTs with a total of 754 participants. Compared with placebo, omega-3, magnesium, vitamin D, zinc, and probiotics were more beneficial for improving FPG, serum insulin, and HOMA-IR. Network analysis showed that vitamin D supplementation was superior to omega-3 (-3.64 mg/dL, 95% CI: -5.77 to -1.51), zinc (-5.71 mg/dL, 95% CI: -10.19 to -1.23), probiotics (-6.76 mg/dL, 95% CI: -10.02 to -3.50), and placebo (-12.13 mg/dL, 95% CI: -14.55 to -9.70) for improving FPG. Magnesium supplementation was more beneficial for decreasing serum insulin compared with probiotics (-5.10 μIU/mL, 95% CI: -9.32 to -0.88) and placebo (-7.80 μIU/mL, 95% CI: -9.32 to -0.88) and placebo (-7.80 .

CONCLUSION

Vitamin D supplementation significantly reduced FPG and regulated HOMA-IR. Magnesium supplementation was superior in decreasing serum insulin than supplementation with other nutrients. Nutrient supplementation seemed to have an effect on glucose homeostasis maintenance in patients with GDM and may be considered an adjunctive therapy.

The Effects of Lifestyle and/or Vitamin D Supplementation Interventions on Pregnancy Outcomes: What Have We Learned from the DALI Studies?

PURPOSE OF REVIEW

The DALI (vitamin D and lifestyle intervention in the prevention of gestational diabetes mellitus (GDM)) study aimed to prevent GDM with lifestyle interventions or Vitamin D supplementation (1600 IU/day). This review summarizes the learnings from the DALI studies among pregnant women with a BMI ≥ 29 kg/m².

RECENT FINDINGS

Women diagnosed with GDM earlier in pregnancy had a worse metabolic profile than those diagnosed later. A combined physical activity (PA) and healthy eating (HE) lifestyle intervention improved both behaviours, limited gestational weight gain (GWG) and was cost-effective. Although GDM risk was unchanged, neonatal adiposity was reduced due to less sedentary time. Neither PA nor HE alone limited GWG or GDM risk. Fasting glucose was higher with HE only intervention, and lower with Vitamin D supplementation. Our combined intervention did not prevent GDM, but was cost-effective, limited GWG and reduced neonatal adiposity.

Joint effects of folate and vitamin B12 imbalance with maternal characteristics on gestational diabetes mellitus

BACKGROUND

This study examined whether folate and vitamin B₁₂ imbalance is associated with gestational diabetes mellitus (GDM) and explored interactions between B vitamin imbalance and maternal risk factors for GDM.

METHODS

A cross-sectional study was performed in 406 Chinese pregnant women. Serum folate, vitamin B₁₂ , and blood glucose concentrations were measured at 24 to 28 weeks gestation during GDM screening. A diagnosis of GDM was made based on International Association of Diabetes and Pregnancy Study Groups criteria (fasting plasma glucose [FPG] ≥5.1 mM, 1-hour plasma glucose ≥10.0 mM, or 2-hour plasma glucose ≥8.5 mM). Binary logistic regression was used to obtain odds ratios (ORs) after controlling for different confounders.

RESULTS

Higher folate levels were associated with higher glucose concentrations and a higher risk of GDM (OR 1.98; 95% confidence interval [CI] 1.00-3.90), whereas higher vitamin B₁₂ levels were associated with lower FPG and a lower risk of GDM (OR 0.30; 95% CI 0.15-0.60). A higher folate: vitamin B₁₂ ratio was associated with higher glucose and a higher risk of GDM (OR 3.08; 95% CI 1.63-5.83). The presence of both a higher folate: vitamin B₁₂ ratio and advanced age further increased the OR to 2.13 (95% CI 1.09-4.15) with a significant additive interaction. Furthermore, a higher folate: vitamin B₁₂ ratio and a higher prepregnancy body mass index (pp-BMI) were synergistically associated with an increased risk of GDM (OR 3.03; 95% CI 1.40-6.57).

CONCLUSIONS

An imbalance between folate and vitamin B₁₂ , represented by a higher folate: vitamin B₁₂ ratio, was highly associated with GDM risk, and this association could be further modified by maternal age and pp-BMI.

Can a Simple Dietary Screening in Early Pregnancy Identify Dietary Habits Associated with Gestational Diabetes?

Gestational diabetes mellitus (GDM) is predominantly a lifestyle disease, with diet being an important modifiable risk factor. A major obstacle for the prevention in clinical practice is the complexity of assessing diet. In a cohort of 1651 Icelandic women, this study examined whether a short 40-item dietary screening questionnaire administered in the 1st trimester could identify dietary habits associated with GDM. The dietary variables were aggregated into predefined binary factors reflecting inadequate or optimal intake and stepwise backward elimination was used to identify a reduced set of factors that best predicted GDM. Those binary factors were then aggregated into a risk score (range: 0–7), that was mostly characterised by frequent consumption of soft drinks, sweets, cookies, ice creams and processed meat. The women with poor dietary habits (score ≥ 5, n = 302), had a higher risk of GDM (RR = 1.38; 95%CI = 3, 85) compared with women with a more optimal diet (score ≤ 2, n = 407). In parallel, a pilot (n = 100) intervention was conducted among overweight and obese women examining the effect of internet-based personalized feedback on diet quality. Simple feedback was given in accordance with the answers provided in the screening questionnaire in 1st trimester. At the endpoint, the improvements in diet quality were observed by, as an example, soft drink consumption being reduced by ~1 L/week on average in the intervention group compared to the controls. Our results suggest that a simple dietary screening tool administered in the 1st trimester could identify dietary habits associated with GMD. This tool should be easy to use in a clinical setting, and with simple individualized feedback, improvements in diet may be achieved.

A simple model to predict risk of gestational diabetes mellitus from 8 to 20 weeks of gestation in Chinese women

Background

Gestational diabetes mellitus (GDM) is associated with adverse perinatal outcomes. Screening for GDM and applying adequate interventions may reduce the risk of adverse outcomes. However, the diagnosis of GDM depends largely on tests performed in late second trimester. The aim of the present study was to bulid a simple model to predict GDM in early pregnancy in Chinese women using biochemical markers and machine learning algorithm.

Methods

Data on a total of 4771 pregnant women in early gestation were used to fit the GDM risk-prediction model. Predictive maternal factors were selected through Bayesian adaptive sampling. Selected maternal factors were incorporated into a multivariate Bayesian logistic regression using Markov Chain Monte Carlo simulation. The area under receiver operating characteristic curve (AUC) was used to assess discrimination.

Results

The prevalence of GDM was 12.8%. From 8th to 20th week of gestation fasting plasma glucose (FPG) levels decreased slightly and triglyceride (TG) levels increased slightly. These levels were correlated with those of other lipid metabolites. The risk of GDM could be predicted with maternal age, prepregnancy body mass index (BMI), FPG and TG with a predictive accuracy of 0.64 and an AUC of 0.766 (95% CI 0.731, 0.801).

Conclusions

This GDM prediction model is simple and potentially applicable in Chinese women. Further validation is necessary.

Electronic supplementary material

The online version of this article (10.1186/s12884-019-2374-8) contains supplementary material, which is available to authorized users.

Long-term vitamin D and high-dose n-3 fatty acids' supplementation improve markers of cardiometabolic risk in type 2 diabetic patients with CHD

This study was performed to evaluate the effects of vitamin D and n-3 fatty acids' co-supplementation on markers of cardiometabolic risk in diabetic patients with CHD. This randomised, double-blinded, placebo-controlled trial was conducted among sixty-one vitamin D-deficient diabetic patients with CHD. At baseline, the range of serum 25-hydroxyvitamin D levels in study participants was 6·3-19·9 ng/ml. Subjects were randomly assigned into two groups either taking 50 000 IU vitamin D supplements every 2 weeks plus 2× 1000 mg/d n-3 fatty acids from flaxseed oil (n 30) or placebo (n 31) for 6 months. Vitamin D and n-3 fatty acids' co-supplementation significantly reduced mean (P = 0·01) and maximum levels of left carotid intima-media thickness (CIMT) (P = 0·004), and mean (P = 0·02) and maximum levels of right CIMT (P = 0·003) compared with the placebo. In addition, co-supplementation led to a significant reduction in fasting plasma glucose (β -0·40 mmol/l; 95 % CI -0·77, -0·03; P = 0·03), insulin (β -1·66 μIU/ml; 95 % CI -2·43, -0·89; P < 0·001), insulin resistance (β -0·49; 95 % CI -0·72, -0·25; P < 0·001) and LDL-cholesterol (β -0·21 mmol/l; 95 % CI -0·41, -0·01; P = 0·04), and a significant increase in insulin sensitivity (β +0·008; 95 % CI 0·004, 0·01; P = 0·001) and HDL-cholesterol (β +0·09 mmol/l; 95 % CI 0·01, 0·17; P = 0·02) compared with the placebo. Additionally, high-sensitivity C-reactive protein (β -1·56 mg/l; 95 % CI -2·65, -0·48; P = 0·005) was reduced in the supplemented group compared with the placebo group. Overall, vitamin D and n-3 fatty acids' co-supplementation had beneficial effects on markers of cardiometabolic risk.

Association between vitamin D status during pregnancy and total gestational weight gain and postpartum weight retention: a prospective cohort

OBJECTIVES

To evaluate the association between vitamin D status during pregnancy and total gestational weight gain (GWG), GWG rates and postpartum weight retention.

METHODS

Prospective cohort of 163 women from Rio de Janeiro was followed at 5^th-13^th (baseline), 20^th-26^th, 30^th-36^th gestational weeks and at 30-62 days postpartum. Plasma 25-hydroxyvitamin D [25(OH)D] was evaluated during each trimester and was categorized as adequate (≥50 nmol/L) or inadequate (<50 nmol/L). GWG (kg) was calculated as the difference between the weight measured at baseline and 36^th-42^th gestational weeks. GWG rates (kg/week) were calculated between each visit. Postpartum weight retention (kg) was analysed as the difference between weights measured at 30-62 days postpartum and 5^th-13^th gestational weeks. Statistical analyses were performed using linear regression models that included interaction terms between vitamin D status and first trimester body mass index (BMI) (<25/≥25 kg/m²). Confounders were selected based on a directed acyclic graph.

RESULTS

The prevalence of vitamin D inadequacy was 16.6%, 9.9% and 10.6% in the first, second and third trimesters, respectively. Overweight women with vitamin D inadequacy in the first (β = 3.70; 95% CI 0.09; 7.31, p-value = 0.045) and third trimester (β = 4.59, 95% CI 0.07; 9.10, p-value = 0.047) presented higher increases in total GWG than did women with vitamin D adequacy. This association was also observed between first trimester vitamin D status and GWG rates between visits 1 and 2 (β = 0.17; 95% CI 0.13; 0.36, p-value = 0.07).

CONCLUSIONS

There was an interaction effect of first trimester BMI (≥25 kg/m²) on the association between first and third trimester vitamin D status and GWG.

The Effect of Vitamin D Supplementation on Glycaemic Control in Women with Gestational Diabetes Mellitus: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Vitamin D deficiency is highly prevalent amongst pregnant women and is linked to a range of adverse complications, including gestational diabetes. However, there is no consensus among researchers regarding the impact of vitamin D supplementation in alleviating adverse effects in gestational diabetes. The objective of this systematic review and meta-analysis was to determine whether supplementation of vitamin D given to women with gestational diabetes can promote glycaemic control. EMBASE and PubMed were searched up to November, 2018. The selection criteria included randomised controlled trials of the effect of vitamin D supplementation (1000-4762 IU/day) on pregnant women with gestational diabetes mellitus. Study data and outcome measures (fasting blood glucose, glycated haemoglobin and serum insulin) were extracted from included studies. Random-effects models were used for meta-analyses. Heterogeneity tests, and analysis of the risk of bias were conducted. Most of the studies were graded as having either low risk or moderate risk of bias although two studies had a high risk of bias in the areas of blinding of participants and personnel, and incomplete outcome data. On the other hand, the heterogeneity statistic (I²) ranged from 0-41% in the studies included. Five randomised controlled trials were selected for this review and meta-analysis (involving a total of 173 participants supplemented with vitamin D and 153 participants as control drawn from the studies). Vitamin D supplementation was associated with a decrease in fasting blood glucose by a mean of 0.46 mmol/L (-0.68, -0.25) (p < 0.001), glycated haemoglobin by a mean of 0.37% (-0.65, -0.08) (p < 0.01) and serum insulin concentration by mean of 4.10 µIU/mL (-5.50, -2.71) (p < 0.001) compared to controls. This review shows evidence that vitamin D supplementation has the potential to promote glycaemic control in women with Gestational Diabetes Mellitus (GDM). However, due to the limited number of studies in the meta-analysis, the conclusion should be interpreted with caution. Further studies are needed to fully understand the exact mechanism by which vitamin D influences glucose metabolism.

The DALI vitamin D randomized controlled trial for gestational diabetes mellitus prevention: No major benefit shown besides vitamin D sufficiency

BACKGROUND & AIMS

As vitamin D deficiency is associated with an increased risk of gestational diabetes mellitus (GDM), we aimed to test vitamin D supplementation as a strategy to reduce GDM risk (evaluated after fasting plasma glucose (FPG), insulin resistance and weight gain) in pregnant overweight/obese women.

METHODS

The DALI vitamin D multicenter study enrolled women with prepregnancy body mass index (BMI) ≥ 29 kg/m², ≤19 + 6 weeks of gestation and without GDM. Participants were randomized to receive 1600 IU/day vitamin D3 or placebo (each with or without lifestyle intervention) on top of (multi)vitamins supplements. Women were assessed for vitamin D status (sufficiency defined as serum 25-hydroxyvitamin D (25(OH)D) ≥ 50 nmol/l), FPG, insulin resistance and weight at baseline, 24-28 and 35-37 weeks. Linear or logistic regression analyses were performed to assess intervention effects.

RESULTS

Average baseline serum 25(OH)D was ≥50 nmol/l across all study sites. In the vitamin D intervention arm (n = 79), 97% of participants achieved target serum vitamin 25(OH)D (≥50 nmol/l) at 24-28 weeks and 98% at 35-37 weeks vs 74% and 78% respectively in the placebo arm (n = 75, p < 0.001). A small but significantly lower FPG (-0.14 mmol/l; CI95 -0.28, -0.00) was observed at 35-37 weeks with the vitamin D intervention without any additional difference in metabolic status, perinatal outcomes or adverse event rates.

CONCLUSION

In the DALI vitamin D trial, supplementation with 1600 IU vitamin D3/day achieved vitamin D sufficiency in virtually all pregnant women and a small effect in FPG at 35-37 weeks. The potential of vitamin D supplementation for GDM prevention in vitamin D sufficient populations appears to be limited.

TRIAL REGISTRATION NUMBER

ISRCTN70595832.

The role of vitamin D in perinatology. An up-to-date review

The role of vitamin D in perinatology is a subject of major interest in current medicine. There is growing evidence about the role of maternal vitamin D levels in pregnancy outcomes. The aim of this review is to summarize the current literature about the role of vitamin D in perinatology. Evidence from this review suggests associations between low levels of maternal vitamin D and higher risk of certain obstetrical complications. Vitamin D has been found to be related to preeclampsia, gestational diabetes mellitus, low birth weight, and preterm birth. The current literature supports vitamin D supplementation in pregnant women, but more high-quality data are necessary. The problem that remains is how to achieve an optimal 25-hydroxyvitamin D level. To determine the real benefits of vitamin D supplementation in pregnancy, we need high-quality trials in larger groups.

The Relationship Between Vitamin D Deficiency and Insulin Resistance in Pregnant Women with Gestational Diabetes

BACKGROUND

Diabetes Mellitus is one of the most common medical disorders in pregnancy. The possibility of vitamin D deficiency as a pathogenesis for impaired glucose tolerance tests show a probable role of vitamin D in insulin secretion and reduction of insulin resistance. This study was assigned to evaluate relation between serum vitamin D level and insulin resistance in Gestational Diabetes Mellitus (GDM).

METHODS

This cross sectional study was done throughout one year between 2015-2016 in GDM patients (age, 20-40 years). After history taking and physical examination, the laboratory tests including : Fasting Blood Sugar (FBS), Glucose Tolerance Test (GTT), calcium, phosphorous, parathormone, 25(OH) vitamin D, insulin, HbA1C, TG, LDL, HDL were performed for all patients. Insulin resistance was calculated according to HOMA-IR formula. Vitamin D level was compared between patients with and without insulin resistance.

RESULTS

This research was performed in 93 GDM patients with average age (30.3 ± 5.6). Thirty eight patients with insulin resistance and 55 patients without insulin resistance were detected. The prevalence of vitamin D deficiency was 91.4% in all patients. There was no significant difference in vitamin D levels between insulin resistant and non insulin resistant group (P-value=0.51). In all variable parameters, only FBS and triglyceride level in insulin resistant group were more than non insulin resistant group (P-value<0.05).

CONCLUSION

Obtained results showed not significant relationship between vitamin D deficiency and insulin resistance in GDM patients.

VDR Variants rather than Early Pregnancy Vitamin D Concentrations Are Associated with the Risk of Gestational Diabetes: The Ma'anshan Birth Cohort (MABC) Study

AIM

This study investigated the associations among early pregnancy vitamin D concentrations, seasonality, and vitamin D metabolic gene variants and how these variables related alone and in interaction with the risk of gestational diabetes mellitus (GDM).

METHODS

Research participants were women from the Ma'anshan birth cohort study in China. The overall study included 3110 women to explore the association between early pregnancy vitamin D concentrations and the risk of GDM. In the current analysis, a nested case-control study of 274 GDM cases and 380 controls was conducted to investigate seven vitamin D metabolic gene variants and the risk of GDM. Vitamin D concentrations were measured by radioimmunoassay. Genotypes were determined by improved multiple ligase detection reaction. Interactions between genetic variants and vitamin D as predictors of the risk of GDM were evaluated by a pair-wise analysis under a multiplicative interaction model.

RESULTS

Vitamin D concentrations were not significantly associated with the risk of GDM (OR = 0.79, 95% CI = 0.55-1.13) after adjusting for seasonality. Fall-winter conceptions had a 37% decreased risk of GDM compared with spring-summer conceptions (OR = 0.63, 95% CI = 0.49-0.81), independent of vitamin D concentrations. Two VDR gene variants rs1544410 (OR = 2.03, 95% CI = 1.17-3.51 for CT versus CC) and rs731236 (OR = 2.42, 95% CI = 1.29-4.55 for GA versus AA) were significantly associated with the risk of GDM. No interactions among genetic variants and vitamin D concentrations were detected.

CONCLUSION

Early pregnancy vitamin D insufficiency or deficiency was not significantly associated with the risk of GDM. The results of this study emphasize the importance of genetic variants in VDR and conception season as factors that affect the risk of GDM.

In utero exposure to extra vitamin D from food fortification and the risk of subsequent development of gestational diabetes: the D-tect study

Background

The primary aim of this study was to assess whether exposure during fetal life to extra vitamin D from food fortification was associated with a reduction in the risk of subsequently developing gestational diabetes mellitus (GDM). Furthermore, we examined whether the effect of the vitamin D from fortification differed by women’s season of birth.

Methods

This semi-ecological study is based on the cancellation in 1985 of the mandatory policy to fortify margarine with vitamin D in Denmark, with inclusion of entire national adjacent birth cohorts either exposed or unexposed to extra vitamin D in utero. The identification of GDM cases later in life among both exposure groups was based on the Danish national health registers. Logistic regression analyses generating odds ratios (ORs) and 95% confidence intervals (95% CIs) were performed.

Results

Women who were prenatally exposed to the extra vitamin D from fortification tended to have a lower risk of subsequently developing GDM than unexposed women (OR 0.87, 95%CI 0.74,1.02, P = 0.08). When analyses were stratified by women’s season of birth, exposed women born in spring had a lower risk of developing GDM compared to unexposed subjects (OR 0.68, 95%CI 0.50,0.94, p = 0.02).

Conclusion

This study suggests that prenatal exposure to extra vitamin D from mandatory fortification may lower the risk of developing gestational diabetes among spring-born women.

Trial registration

This study is part of the D-tect project, which is registered on clinicaltrials.gov: NCT03330301.

Electronic supplementary material

The online version of this article (10.1186/s12937-018-0403-5) contains supplementary material, which is available to authorized users.

Systematic review and meta-analysis of Spanish studies regarding the association between maternal 25-hydroxyvitamin D levels and perinatal outcomes

Objective: This systematic review and meta-analysis of Spanish studies assessed the association of maternal 25-hydroxyvitamin D [25(OH)D] levels on perinatal outcomes. Methods: PubMed, Cochrane Library, Embase, Scielo, Scopus, and Web of Science research databases were searched from inception through December 30 2017 using the terms 'vitamin D', 'pregnancy', and 'Spain'. Studies that compared first or second half of pregnancy normal 25(OH)D (≥30.0 ng/mL) versus insufficient (20.0-29.9 ng/mL) or deficient (<20.0 ng/mL) circulating levels and perinatal outcomes were systematically extracted. Data are presented as pooled odds ratios and their 95% confidence intervals (CIs) for categorical variables or mean differences and CIs for continuous variables. Risk of bias was evaluated with the Newcastle-Ottawa Scale. Results: Five cohort studies met inclusion criteria. The risk of gestational diabetes mellitus, preeclampsia, preterm birth, and small-for-gestational-age infants, and birthweight was not influenced by first half of pregnancy maternal 25(OH)D levels. In addition, second half of pregnancy 25(OH) levels did not affect birthweight. Conclusion: Maternal 25(OH)D levels during pregnancy did not affect studied perinatal outcomes and birthweight.

The Role of Vitamin D in Fertility and during Pregnancy and Lactation: A Review of Clinical Data

Vitamin D deficiency is common and there exists a huge gap between recommended dietary vitamin D intakes and the poor vitamin D supply in the general population. While vitamin D is important for musculoskeletal health, there are accumulating data suggesting that vitamin D may also be important for fertility, pregnancy outcomes and lactation. Significant changes in vitamin D metabolism during pregnancy such as increased production of the “active vitamin D hormone” calcitriol support the important role of vitamin D in this setting. Observational studies show that vitamin D deficiency is a risk marker for reduced fertility and various adverse pregnancy outcomes and is associated with a low vitamin D content of breast milk. Meta-analyses of randomized controlled trials (RCTs) document that physiological vitamin D supplementation during pregnancy is safe and improves vitamin D and calcium status, thereby protecting skeletal health. Although certain RCTs and/or meta-analyses reported some other beneficial effects, it is still not clear whether vitamin D supplementation improves fertility or decreases the risk of adverse pregnancy outcomes such as low birth weight, pre-eclampsia and neonatal mortality, or reduces wheeze/asthma in the infants. Nevertheless, vitamin D supplementation in pregnant women is frequently required to achieve a sufficient vitamin D status as recommended by nutritional vitamin D guidelines. In this review, we provide an overview of systematic reviews, meta-analyses and large trials reporting clinical data on the role of vitamin D for fertility, pregnancy and lactation.

Association of type 2 diabetes susceptible genes GCKR, SLC30A8, and FTO polymorphisms with gestational diabetes mellitus risk: a meta-analysis

PURPOSE

Current studies have detected the correlation of polymorphisms in type 2 diabetes susceptible genes GCKR, SLC30A8 and FTO with gestational diabetes mellitus (GDM) risk. However, findings of these studies were incongruous. Hence, we performed an integrated review and meta-analysis for the researches regarding the association of single nucleotide polymorphisms (SNPs) in GCKR, SLC30A8 and FTO genes and GDM risk.

METHODS

Eligible publications were selected on the basis of several inclusion and exclusion criteria. Correlation between each SNP and GDM risk was estimated by computing odds ratios (ORs) with 95% confidence intervals (95%CIs).

RESULTS

Consequently, 19 case-control studies (from 16 citations) including 3636 GDM cases and 7229 GDM-free controls were participated in a meta-analysis of seven prevalent SNPs (GCKR rs1260326 and rs780094; SLC30A8 rs13266634 and rs11558471; FTO rs8050136, rs1421085 and rs9939609). Our results demonstrated that the rs780094, rs13266634 and rs9939609 SNPs were significantly associated with GDM risk. In stratified analysis, correlations of rs780094 and rs13266634 SNPs could be observed in Asian and Caucasian subgroups. Moreover, association between rs9939609 SNP and GDM risk was detected in Caucasian subgroup.

CONCLUSIONS

The GCKR rs780094, SLC30A8 rs13266634 and FTO rs9939609 SNPs were demonstrated to be the potential biomarkers for GDM risk prediction.

The Association of Vitamin D Levels with Common Pregnancy Complications

The association between vitamin D deficiency and various adverse pregnancy outcomes has been extensively investigated in recent years. The pregnant woman is the only source of vitamin D for the foetus. The main sources of vitamin D for pregnant women are sunlight, fortified dairy products, oily fish and dietary supplements. Vitamin D deficiency during pregnancy has been associated with some adverse neonatal outcomes as well as an increased risk of late pregnancy complications. The outcomes of the published studies investigating preeclampsia and gestational diabetes mellitus vary with some large trials suggesting a potential positive effect of vitamin D supplementation during pregnancy on the decreased risk of these complications. Research also suggests a possible connection between lower vitamin D concentrations and increased risk of preterm labour. In our manuscript, we aim to review the existing literature regarding the prevalence of vitamin D deficiency during pregnancy, the factors associated with vitamin D deficiency, and possible pregnancy complications arising from it.