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Head-to-head evidence comparison — which supplement is right for you?
B-Complex vs Vitamin D3: Vitamin D3 has the stronger overall evidence (7.5 vs 6.5/10); they're alternatives for bone health — the best pick depends on your goals. Take the 60-second quiz for a pick tailored to your goals.
Vitamin D3 wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Probably helps
5 of 8 studies with measurable effects showed benefit.
Top outcomes
Verdict
Probably helps
15 of 26 studies with measurable effects showed benefit.
Top outcomes
1 capsule daily (per label)
Morning with breakfast
Methylated B-complex (methylcobalamin, methylfolate)
2000-4000 IU daily
Morning with breakfast
D3 (cholecalciferol) softgel or liquid
and 1 more not shown
2-4 weeks
4-8 weeks
Immediate
4-8 weeks
4-8 weeks
2-4 weeks
4-8 weeks
Dosage exploration of combined B-vitamin supplementation in stroke prevention: a meta-analysis and systematic review
The American journal of clinical nutrition (2024) · Meta analysis · n=76664
In areas without and with partial folic acid fortification, combined B-vitamin supplementation significantly reduced the risk of stroke by 34% [RR: 0.66; 95% confidence interval (CI): 0.50, 0.86] and 11% (RR: 0.89; 95% CI: 0.79, 1.00), respectively.
A Comparative Study Evaluating the Effectiveness of Folate-Based B Vitamin Intervention on Cognitive Function of Older Adults under Mandatory Folic Acid Fortification Policy: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
Nutrients (2024) · Meta analysis · n=42768
The meta-analysis on the effects of folate-based B vitamin supplementation on cognitive function showed a significant overall impact (Z = 3.84; p = 0.0001; SMD, 0.18; 95% CI, 0.09, 0.28).
A Systematic Review and Meta-Analysis of B Vitamin Supplementation on Depressive Symptoms, Anxiety, and Stress: Effects on Healthy and 'At-Risk' Individuals
Nutrients (2019) · Meta analysis · n=2015
Regarding individual facets of mood, B vitamin supplementation benefited stress (n = 958, SMD = 0.23, 95% CI = 0.02, 0.45, p = 0.03).
Vitamin D supplementation vs. placebo and incident type 2 diabetes in an ancillary study of the randomized Vitamin D and Omega-3 Trial
Nature communications (2025) · Meta analysis · n=5205
Mean body mass index (BMI) was 27.5 kg/m2 (SD = 5.3), with 51% female and 17% Black race/ethnicity.
Vitamin D Supplementation for Patients with Dysmenorrhoea: A Meta-Analysis with Trial Sequential Analysis of Randomised Controlled Trials
Nutrients (2024) · Meta analysis · n=687
TSA revealed that the current RCTs provide sufficient information.
Vitamin D and respiratory tract infections
BMJ (2017) · Meta analysis · n=11321
12% reduction in respiratory infections overall
Multiple meta-analyses show small but statistically significant benefits for cognitive function in older adults and stroke prevention populations. Effect sizes are modest (SMD ~0.15-0.18). Benefits may be more pronounced in B-vitamin deficient populations.
Meta-analysis showed 12% overall reduction in respiratory infections, with greater benefits in severely deficient individuals. Daily dosing more effective than bolus. Conservative estimate assumes most users not severely deficient.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin D3 has a higher evidence score (7.5/10 vs 6.5/10) and wins in 2 of 3 categories.
For bone health, Vitamin D3 has a higher relevance score (92 vs 70).
No known interactions between B-Complex and Vitamin D3 have been documented in our database. However, always consult a healthcare provider before combining supplements.
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The transition years (40s): cycle changes, mood, sleep, brain fog — foundations, vitex, and starting muscle work early.
When to take what, with or without food, and which supplements compete vs pair well.
The honest tier list — proven staples vs situational vs mostly marketing. The hub the other guides feed into.
The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.