Vitamin D2 & Prediabetes: Does It Help Your Heart?

observational-study PMID: 26700109

Quick Summary: A study looked at whether taking high doses of Vitamin D2 or D3 could help people with prediabetes. The results showed that while it didn't lower blood sugar, it might help improve artery health.

Does Vitamin D2 Help With Blood Sugar?

This research investigated if taking Vitamin D2 (ergocalciferol) or Vitamin D3 (cholecalciferol) could help people at risk of type 2 diabetes. The study found that taking either type of Vitamin D for four months didn't lower their blood sugar levels (measured by HbA1c).

What About Heart Health?

The study did find a small benefit for heart health. Both Vitamin D2 and D3 seemed to slightly improve artery stiffness, which is a measure of how well your arteries are working.

Study Details

Who was studied: 340 adults who were at risk of developing type 2 diabetes (they either had prediabetes or a high risk score).

How long: The study lasted for 4 months.

What they took: Participants were given either:

A placebo (a "dummy" pill)
100,000 IU of Vitamin D2 (ergocalciferol) once a month
100,000 IU of Vitamin D3 (cholecalciferol) once a month

What This Means For You

If you have prediabetes: Taking high doses of Vitamin D2 or D3 might help your arteries, but it won't lower your blood sugar.

Talk to your doctor: Always discuss any supplements with your doctor, especially if you have health concerns. They can help you decide if Vitamin D is right for you and what dose is best.

Focus on the basics: Remember that lifestyle changes like a healthy diet and exercise are still the most important things you can do to manage prediabetes and protect your heart.

Study Limitations

Short study: The study only lasted 4 months, so we don't know if the effects would last longer.

High doses: The study used very high doses of Vitamin D, which is different from the amount you might get in a daily supplement.

Specific group: The results only apply to people with prediabetes, not the general population.

Small benefit: The improvement in artery health was small, so more research is needed.

Key Findings

This 2016 study found that 4 months of monthly vitamin D supplementation (100,000 IU D2 or D3) did not improve glycated hemoglobin (HbA1c) levels in adults at elevated risk of type 2 diabetes. However, both D2 and D3 reduced pulse wave velocity (PWV)—a marker of arterial stiffness—compared to placebo, suggesting potential cardiovascular benefits. No significant effects were observed on blood pressure, lipids, or other cardiometabolic metrics.

Study Design

This was a randomized, double-blind, placebo-controlled trial conducted over 4 months. The sample included 340 adults with non-diabetic hyperglycemia or a positive diabetes risk score, indicating prediabetes. Participants were randomized into three groups: placebo, vitamin D2 (ergocalciferol), or vitamin D3 (cholecalciferol).

Dosage & Administration

Participants received 100,000 IU of vitamin D2 or D3 orally once monthly for 4 months. Placebo groups received identical inactive capsules. Supplementation aimed to address vitamin D deficiency, with baseline 25(OH)D levels averaging 5.2 nmol/l in the D2 group and 45.8 nmol/l in the D3 group.

Results & Efficacy

HbA1c: No significant changes were observed. D2 vs. placebo: -0.05% (-0.51 mmol/mol; 95% CI -1.16, 0.14; p=0.13). D3 vs. placebo: +0.02% (+0.19 mmol/mol; 95% CI -0.46, 0.83; p=0.57).
Arterial Stiffness (PWV): Both D2 and D3 reduced PWV modestly. D2 vs. placebo: -0.68 m/s (95% CI -1.31, -0.05). D3 vs. placebo: -0.73 m/s (95% CI -1.42, -0.03).
Safety: No major adverse effects were reported.

Limitations

Short Duration: The 4-month intervention may be insufficient to detect long-term metabolic or cardiovascular effects.
High-Dose Bolus: Monthly 100,000 IU doses differ from daily regimens, potentially affecting bioavailability and outcomes.
Population Specificity: Results apply only to adults with prediabetes or elevated diabetes risk, not the general population.
Secondary Outcome Focus: PWV improvements were statistically significant but modest in magnitude, requiring validation in larger trials.
Baseline Variability: The D2 group had lower baseline 25(OH)D levels than the D3 group, which might influence response to supplementation.

Clinical Relevance

For individuals at risk of type 2 diabetes, short-term high-dose vitamin D supplementation (D2 or D3) does not improve glycemic control (HbA1c) but may slightly reduce arterial stiffness. However, the clinical significance of the PWV reduction is uncertain, and longer-term studies are needed to assess durability and broader cardiometabolic impacts. The safety profile supports monthly dosing in this population, though daily regimens or combination therapies might yield different results. Patients should prioritize established diabetes prevention strategies (e.g., diet, exercise) over relying on vitamin D alone.

Note: This analysis is specific to the 2016 trial (PubMed ID 26700109) and does not generalize to other populations, dosing protocols, or vitamin D forms.

Vitamin D2 & Prediabetes: Does It Help Your Heart?