Low first trimester vitamin D associated with gestational diabetes

New research suggests that pregnant women who are vitamin D deficient during their first trimester are at significantly greater risks of developing gestational diabetes mellitus (GDM) later during that pregnancy.

The study’s findings were presented in Berlin, Germany, at the 48th annual meeting of the European Association for the Study of Diabetes by Marilyn Lacroix from the University of Sherbrooke in Quebec, Canada.

Sources and functions of Vitamin D

Vitamin D is synthesised in the skin during sunlight exposure but can also be obtained from the diet — oily fish like salmon, mackerel and sardines; eggs, powdered milk, beef liver, fortified margarines and breakfast cereals. Individuals at risk of vitamin D deficiency include all pregnant and breastfeeding women; those who do not get much sun exposure (such as women who cover up their skin when outdoors); and dark-skinned people of African, African-Caribbean and South Asian origins.

1,25-dihydroxyvitamin D, the active form of Vitamin D, is produced from 25-hydroxyvitamin D (25OHD). Known to be involved in bone mineralisation and calcium absorption, 1,25-dihydroxyvitamin D is now suspected to regulate blood glucose (sugar) levels.

Study design

A total of 655 healthy women, aged 18 and above, at 6 to 13 weeks’ gestation were recruited from Sherbrooke, a region with relatively lower sun exposure compared to southern areas. 25OHD levels were measured and three anthropometric indices (BMI, waist circumference and percentage body fat) were recorded upon enrolment. Between the 24th and 28th weeks of pregnancy, these women were assessed for diabetes.

Women with a history of diabetes (types 1 or 2) or GDM in the first trimester; multiple pregnancy, miscarriage, or known to abuse alcohol or drugs, were excluded from the study.

Study findings

54 women, 8.2% of the research group, developed GDM. Referring to first trimester baseline characteristics, the researchers observed that, compared to women with normal glucose tolerance, subjects with GDM were older and had higher adiposity, as indicated by higher waist circumference, BMI and body fat percentage.

“The mean total 25OHD levels in our cohort was about 63nmol/L, and participants with gestational diabetes mellitus had lower levels of 25OHD compared to normal glucose tolerant women,” stated Lacroix.”The overall prevalence of vitamin D deficiency in our cohort was about 27%.”

The scientists concluded that vitamin D deficiency (blood levels below 50nmol/L) during the first trimester is associated with an increased risk for GDM: among the women with low vitamin D levels early during pregnancy, 37% developed GDM in the second trimester and only 26% remained glucose tolerant.

“Per each decrease of [18.8nmol/L] of 25OHD levels, the risk of developing gestational diabetes mellitus increases by 37% and this remained statistically significant after adjustment for age, season of blood sampling, vitamin D supplementation or any of the three adiposity measurements,” reported Lacroix.

According to Lacroix, vitamin D deficiency is related to insulin resistance but not to insulin secretion or compensation of β-cells (insulin producing cells in the pancreas) after considering cofounders.

A European study is currently underway to determine whether GDM can be averted with vitamin D supplementation.