Vitamin D enhances calcium absorption
Vitamin D is essential for proper calcium absorption in the gut. Without adequate D, only 10-15% of dietary calcium is absorbed.
Ensure adequate vitamin D status when supplementing calcium.
Can take together
Vitamin D enhances calcium absorption. Ensure adequate vitamin D status when supplementing calcium.
Can take together
This interaction is rated “Synergy” by Formulate. Vitamin D is essential for proper calcium absorption in the gut. Without adequate D, only 10-15% of dietary calcium is absorbed.
Studies from our registry that mention calcium or vitamin d. Each links to the primary source and the other Formulate pages citing it.
Mentions vitamin d · 2022
The D-Health Trial: a randomised controlled trial of the effect of vitamin D on mortality
Neale et al. · The Lancet Diabetes & Endocrinology
D-HEALTH trial (n=21,315). Monthly 60,000 IU vitamin D did not reduce all-cause mortality over 5 years.
Mentions vitamin d · 2019
Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease
Manson et al. · New England Journal of Medicine
VITAL trial (n=25,871). 2,000 IU/day D3 did not significantly reduce cancer incidence or cardiovascular events in a generally replete population.
Mentions vitamin d · 2017
Monthly High-Dose Vitamin D Supplementation and Cardiovascular Disease (ViDA)
Scragg et al. · JAMA Cardiology
ViDA trial (n=5,110). Monthly high-dose vitamin D did not reduce cardiovascular events.
Mentions vitamin d · 2017
Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data
Martineau AR, Jolliffe DA, Hooper RL, et al. · BMJ
Individual-participant meta-analysis of 25 RCTs (n=10,933) found vitamin D supplementation reduced risk of acute respiratory tract infection, with greatest benefit in baseline-deficient participants and daily/weekly (not bolus) dosing.
Mentions vitamin d · 2015
Dietary fat increases vitamin D-3 absorption
Dawson-Hughes et al. · Journal of the Academy of Nutrition and Dietetics
Monounsaturated-fat-rich meal increased vitamin D3 absorption by ~32% compared to low-fat meal.
Mentions calcium · 2015
Calcium intake and risk of fracture: systematic review
Bolland et al. · BMJ
Systematic review finding little evidence that increasing calcium intake prevents fractures in community-dwelling adults.
Roundup
Best Vitamin D Supplements 2026: Ranked by Clinical Evidence
42% of adults are deficient. Learn which D3 form, dose, and brand actually raises blood levels — with cofactor guidance and lab-verified picks.
Review
Vitamin D3 vs D2: The Science Behind the 87% Gap
D3 raises blood levels 87% more effectively than D2 — and your prescription vitamin D might be the inferior form. Here's what to know.
Other interactions to know
Calcium significantly reduces iron absorption
Calcium blocks thyroid medication absorption
High calcium can impair magnesium absorption
Calcium may reduce zinc absorption
PPIs reduce calcium carbonate absorption
Vitamin D and K2 work synergistically
Magnesium needed for vitamin D activation
Fat improves vitamin D absorption
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Medical disclaimer. This page is for educational purposes only and does not replace advice from a qualified healthcare provider.
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