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Head-to-head evidence comparison — which supplement is right for you?
Calcium vs Vitamin D3: Vitamin D3 has the stronger overall evidence (7.5 vs 5.5/10); they work on different things and are often used together, not either/or. Take the 60-second quiz for a pick tailored to your goals.
Vitamin D3 wins 3 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Too few graded studies
Top outcomes
Verdict
Probably helps
7 of 14 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (2)
Outcomes where both Calcium and Vitamin D3 have evidence — compare verdict strength side-by-side.
1000–1200mg daily (split doses) (no cited trial states the dose it used)
Split doses with meals, 500mg with breakfast, 500mg with dinner
Calcium Citrate
2000-4000 IU daily
Morning with breakfast
D3 (cholecalciferol) softgel or liquid
and 7 more not shown
and 1 more not shown
Vitamin D raises intestinal calcium absorption. In a Cochrane review of older people, vitamin D plus calcium slightly lowered hip and other fractures, while vitamin D alone did not.
Can be taken together. In older people the pair slightly lowered fracture risk in trials.
6-24 months
12-36 months
Throughout pregnancy
Within days of starting
4-8 weeks
4-8 weeks
2-4 weeks
4-8 weeks
Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis
Lancet (2007) · Meta analysis · n=63897
29 randomised trials, 63,897 participants aged 50 or older, pooled with a random-effects model.
Role of calcium and/or vitamin D supplementation in preventing osteoporotic fracture in the elderly: a systematic review and meta-analysis
Indian J Med Res (2023) · Meta analysis
18 RCTs in adults over 60, comparing calcium, vitamin D or both against no treatment or placebo.
Calcium and vitamin D for increasing bone mineral density in premenopausal women
Cochrane Database Syst Rev (2023) · Systematic review · n=941
7 RCTs, 941 healthy premenopausal women: 138 randomised to calcium, 110 to vitamin D, 271 to both, 422 to placebo. Mean ages 18.1 to 42.1.
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) · Rct · n=22220
Ancillary analysis of VITAL: 22,220 adults without T2D randomized to vitamin D3 2000 IU/day or placebo, with a meta-analysis of 3 additional trials.
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
25 RCTs, 11 321 participants aged 0 to 95 years. Vitamin D reduced acute respiratory tract infection overall (adjusted OR 0.88, 95% CI 0.81 to 0.96).
Both points come from a meta-analysis of double-blind cholecalciferol trials in people aged 60 and over (PMID 15886381). Trials at 700 to 800 IU a day cut hip fracture risk by 26% (RR 0.74) and non-vertebral fractures by 23%, plotted at 800 IU. Trials at 400 IU a day showed no benefit (hip fracture RR 1.15), and the WHI trial of 400 IU with 1,000 mg calcium did not significantly reduce hip fracture (PMID 16481635). Most of these trials also gave calcium, and the Cochrane review found vitamin D alone unlikely to prevent fractures while vitamin D with calcium gave a small reduction (PMID 24729336). Doses above 800 IU were not compared, so no optimal dose or ceiling is set.
AI-estimated from published studies. Interpret as directional guidance.
Vitamin D3 has a higher evidence score (7.5/10 vs 5.5/10) and wins in 3 of 3 categories.
For bone health, Calcium has a higher relevance score (95 vs 92).
Calcium and Vitamin D3 may work well together: Vitamin D raises intestinal calcium absorption. In a Cochrane review of older people, vitamin D plus calcium slightly lowered hip and other fractures, while vitamin D alone did not. Can be taken together. In older people the pair slightly lowered fracture risk in trials.
Hot flashes, bone, sleep, muscle — the basics that hold up vs the phytoestrogen hype.
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.
On Ozempic/Wegovy/Mounjaro? What actually helps — muscle preservation, GI relief, nutrient gaps (no upsell).
The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.