Vitamin D3 vs. D2: Which Is Best?

meta-analysis PMID: 22552031

Quick Summary: Research shows that vitamin D3 is more effective than vitamin D2 at raising your vitamin D levels. This means your body uses D3 better than D2.

What The Research Found

A review of multiple studies found that vitamin D3 is significantly better at increasing vitamin D levels in your blood compared to vitamin D2. Think of it like this: D3 is a more powerful form of vitamin D. The studies showed that D3 raised vitamin D levels up to three times more than D2.

Study Details

Who was studied: 508 adults (ages 18-84) with varying levels of vitamin D.

How long: Studies lasted from 6 to 12 weeks.

What they took: Participants took either vitamin D2 or vitamin D3 in different doses, from weekly to daily.

What This Means For You

Choose D3: If you're taking a vitamin D supplement, opt for vitamin D3 (cholecalciferol) over D2 (ergocalciferol).

Talk to your doctor: If you're concerned about your vitamin D levels, get a blood test and discuss the best supplement and dosage for you with your doctor.

D3 is more effective: D3 is more effective at raising your vitamin D levels, which is important for bone health, immune function, and overall well-being.

Study Limitations

Different Doses: The studies used different doses of vitamin D, which could affect the results.

Short-Term Studies: The studies were relatively short, so we don't know the long-term effects of D2 vs. D3.

Adults Only: The research primarily focused on adults, so the findings may not apply to children.

More Research Needed: While this study shows D3 is better, more research is needed to understand the full picture.

Key Findings

The meta-analysis concluded that vitamin D3 supplementation significantly increases serum 25-hydroxyvitamin D [25(OH)D] levels compared to D2. The pooled mean difference was 15.8 nmol/L (95% CI: 8.3–23.4, p < 0.001), indicating D3’s superior efficacy. Subgroup analyses confirmed D3 outperformed D2 in both short-term (<12 weeks) and long-term supplementation, with D2 showing reduced potency at higher doses.

Study Design

This 2012 systematic review and meta-analysis evaluated 10 randomized controlled trials (RCTs) comparing D2 and D3. The total sample included 508 participants (adults aged 18–84 years) with baseline 25(OH)D levels ranging from deficient to sufficient. Study durations varied from 6 weeks to 12 weeks. Trials were sourced from PubMed, with inclusion criteria requiring direct comparison of D2 and D3 effects on serum 25(OH)D.

Dosage & Administration

Doses ranged from 50,000 IU/week to daily supplementation (equivalent to ~800–5000 IU/day). Both forms were administered orally, with some trials using bolus dosing (e.g., single high-dose injections) and others daily/microdosing regimens. D2 doses were often matched to D3 in IU equivalents, though D3 showed greater bioavailability regardless of dosing frequency.

Results & Efficacy

Vitamin D3 increased serum 25(OH)D by 1.8–3.0 times more than D2 across trials. The standardized mean difference (SMD) was 0.41 (95% CI: 0.17–0.64, p = 0.001), favoring D3. In trials with daily dosing, D3 raised levels by 2.2x compared to D2 (p = 0.003). High-dose D2 (>50,000 IU/week) showed diminished efficacy relative to D3, with a 20% lower increase in 25(OH)D (p = 0.02).

Limitations

Heterogeneity: Trials varied in dosing, duration, and baseline 25(OH)D levels (I² = 72%), potentially affecting pooled results.
Population bias: Most participants were adults with mild deficiency or sufficient status; findings may not generalize to severely deficient individuals or children.
Short-term focus: Studies lasted ≤12 weeks, limiting insights into long-term (>6 months) efficacy or safety differences.
Publication bias: Only PubMed was searched, possibly excluding non-English or unpublished data.
Mechanistic gaps: The analysis did not explore differences in metabolism, receptor binding, or clinical outcomes (e.g., bone health).

Clinical Relevance

For supplement users, vitamin D3 is more effective than D2 in raising serum 25(OH)D, particularly at standard daily doses. Clinicians should prioritize D3 for correcting deficiencies or maintaining optimal levels. However, the study does not address whether D2 suffices for individuals with minimal sun exposure or malabsorption issues. Future research should evaluate clinical endpoints and diverse populations to refine recommendations.

Note: This analysis is specific to the 2012 meta-analysis; broader conclusions about vitamin D require additional evidence.