What kind of interaction is it?

Synergy: a documented combination effect that is stronger or more useful than either substance taken alone.

Is this interaction backed by published research?

Yes. NutriStack lists 2 citation rows for the Metformin + Vitamin D3 pair, each linking to PubMed by PMID where available. Full sourcing methodology at https://nutristackapp.com/methodology/interactions.

Interaction databaseSupplement × PrescriptionReviewed May 2026

Metformin and Vitamin D3, a synergy.

Q: Can I take Metformin and Vitamin D3 together?

Yes. The combination of Metformin and Vitamin D3 produces a measurable benefit. Vitamin D deficiency is common in type 2 diabetes and is associated with insulin resistance. Meta-analyses of vitamin D supplementation in type 2 diabetes show small but consistent reductions in fasting glucose, HbA1c, and HOMA-IR, and in prediabetes vitamin D supplementation modestly reduces progression to type 2 diabetes. Combined with metformin the effect is complementary, with low hypoglycemia risk.

Q: How does this affect a NutriStack Stack Score?

+2 to your Stack Score per scored synergy row.

Vitamin D deficiency is common in type 2 diabetes and is associated with insulin resistance. Meta-analyses of vitamin D supplementation in type 2 diabetes show small but consistent reductions in fasting glucose, HbA1c, and HOMA-IR, and in prediabetes vitamin D supplementation modestly reduces progression to type 2 diabetes. Combined with metformin the effect is complementary, with low hypoglycemia risk.

2 primary source citations. Moderate evidence. Last verified May 30, 2026.

Open the interaction checker →Read the methodology

One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.

Sourcing standards·Evidence tiers

From the interaction database

What the row says.

Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.

At a glance

Substances: Metformin and Vitamin D3
Pair type: Synergy
Evidence (highest tier): Moderate
Source citations: 2 sources
Stack Score effect: +2 to your Stack Score (per scored synergy row).
Scope: Supplement × Prescription
Last verified: May 30, 2026

Synergy · Moderate evidence

Synergy

What is happening. Vitamin D deficiency is common in type 2 diabetes and is associated with insulin resistance. Meta-analyses of vitamin D supplementation in type 2 diabetes show small but consistent reductions in fasting glucose, HbA1c, and HOMA-IR, and in prediabetes vitamin D supplementation modestly reduces progression to type 2 diabetes. Combined with metformin the effect is complementary, with low hypoglycemia risk.

Mechanism. Vitamin D modulates insulin secretion via vitamin D receptors on pancreatic beta cells and improves insulin sensitivity by reducing chronic inflammation and influencing calcium signaling in insulin target tissues. Metformin lowers hepatic glucose output via AMPK activation. The mechanisms are independent and complementary.

Recommendation. If you take metformin and have low 25-OH vitamin D, supplementation (typically 1000-4000 IU/day, titrated to a 25-OH level above 30 ng/mL) is reasonable. Routine glucose monitoring is sufficient; hypoglycemia is unlikely unless you also take insulin or a sulfonylurea.

Sources (2)

Stack Score

How this pair moves the number.

Effect on the composite score

If both Metformin and Vitamin D3 are in the same stack, this pair applies +2 to your Stack Score (per scored synergy row).

The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.

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