Vitamin D May Have Protective Effect Against Type 2 Diabetes


Higher levels of vitamin D may reduce the odds of having higher fasting plasma gluclose and hemoglobin A1c levels.

Poonam Pannu, MPH

Australian researchers have found that higher levels of 25-hydroxyvitamin D (25OHD) may reduce the odds of having higher fasting plasma gluclose (FPG) and hemoglobin A1c (HbA1c) levels, thereby conferring a protective effect against type 2 diabetes (T2D).

The study of the 2009-2010 Victorian Health Monitor survey was produced by the Department of Health and Human Services in Victoria, Australia, and the analysis of the study was led by Poonam Pannu, MPH, a PhD candidate at Curtin University in Australia. Pannu and colleagues from Curtin University and the Department of Health in Melbourne point out that vitamin D levels, as determined by 25OHD testing, has become a concern in the medical community due to a prevalence of vitamin D deficiencies in patients which can lead not only to extra-skeletal effects, but myriad other adverse health outcomes.

Pannu and colleagues explained that “accumulating evidence has indicated that higher 25OHD status may have several anti-diabetic effects including improvement in insulin sensitivity, stabilizing HbA1c levels, and improving beta cell function, whereas low 25OHD status may increase risk of T2D.” The researchers set out to investigate any associations between vitamin D levels and the risk of T2D independent of other lifestyle factors and components of metabolic syndrome (MetS).

Using data from the Victorian Health Monitor, a state-wide, cross-sectional population-based survey that included physical, dietary behavior, and biomedical information collected by Department of Health staff, the team analyzed FPG, HbA1c, and 25OHD levels in 3393 patients between the ages of 17 and 75 years.

Cut-offs established by the American Diabetes Association (ADA) for FPG and HbA1c were used to determine risk of T2D, and the researchers used a binary variable to denote low or high risk for T2D based on those levels (FPG <5.6 mmo/L [low risk, normal], vs 5.6 mmol/L ± 6.9 mmol/L [high risk], and HbA1c <5.7% [low risk, normal] vs. 5.7% ± 6.4% [high risk]).

The 25OHD concentration data were divided into low (median, 33 nmol/L; range, 10 nmol/l to 44 nmol/l), medium (median, 54 nmol/L; range, 45 nmol/L ± 65 nmol/L), and high (median, 77 nmol/L; range, 65 nmol/L ± 204 nmol/L) groups for statistical analysis.

To isolate the effect of 25OHD levels from other extenuating factors, the researchers adjusted for socio-demographic, dietary, and biomedical factors. A variety of socio-demographic factors, such as age, gender, relative socio-economic disadvantage, and smoking status, were considered as confounders and adjusted for, as was season of biomedical assessment (which could account for variations in vitamin D levels due to sun exposure). Dietary factors were included in the analysis based as continuous variables, as were biomedical factors with known associations to FPG and HbA1c, such as MetS components, cholesterol, triglycerides, blood pressure, waist circumference, and body mass index.

After adjusting for socio-demographic, dietary, and biomedical variables, the data revealed that for every 10 nmol/L increase in serum 25OHD, there was a significant reduction in the adjusted odds ratio (AOR) for higher FPG (AOR 0.91, [0.86, 0.97]; P = 0.002) and HbA1c (AOR 0.94, [0.90, 0.98]; P = 0.009).

The researchers also discovered that after adjusting for variables in the low, medium, and high 25OHD groupings, study participants with high 25OHD (65 nmol/L ± 204 nmol/L) had statistically significant reduced odds of higher FPG (39%) and higher HbA1c (26%) compared with study participants with low 25OHD (10 nmol/L ± 44 nmol/L).

According to Pannu and colleagues the “significant inverse association” between 25OHD and FPG and HbA1c levels “persisted after the adjustment for a number of socio-domographic, diatary, and biomedical variables and MetS components.” The researchers theorize that the beneficial effects of vitamin D (25OHD) in risk reduction is connected to its effect on insulin secretion, and that when there is a deficiency of vitamin D, insulin secretion is diminished. The researchers also theorize that vitamin D levels may “indirectly influence insulin action via a calcium mediated effect” wherein 25OHD regulates calcium levels which ensure “effective action of insulin within different tissues.” Vitamin D levels may also, according to Pannu and colleagues, play a role in reducing chronic inflammation leading to increased risk factors for a variety of diseases. Pannu and colleagues suggest more research about the causal role vitamin D plays in development or prevention of T2D is needed to provide further insight into the association between 25OHD and T2D.

The article, “Vitamin D status is inversely associated with markers of risk for type 2 diabetes: A population based study in Victoria, Australia.” was published June 2, 2017 on PLOS ONE.


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