Quick summary
The Vitamin D It is a fat-soluble prohormone whose active form (calcitriol) acts on the VDR receptor, present in most human tissues. It regulates calcium and phosphorus metabolism, innate and adaptive immunity, and neuromuscular function. 25-OH-D deficiency is extremely common and reversible with supplementation and sun exposure.
Mechanism of action
Vitamin D3 (cholecalciferol) is synthesized in the skin by the action of UVB radiation or obtained from diet and supplements. It undergoes double hydroxylation: in the liver to 25-OH-D (calcidiol, a storage marker) and in the kidney to 1,25-OH-D (calcitriol, the active form).
- VDR Receiver: Calcitriol regulates the transcription of more than a thousand genes.
- Calcium/phosphorus: It increases intestinal absorption and modulates PTH.
- Immunity: It modulates macrophages and T lymphocytes; it induces antimicrobial peptides such as cathelicidin.
Clinical evidence
- Martineau AR. et al. BMJ 2017 — Meta-analysis of individual data: supplementation reduces acute respiratory infections, with a greater effect in deficient individuals.
- Bischoff-Ferrari HA. et al. JAMA 2004 — Muscle function and reduction of falls in older adults.
- Holick MF. N Engl J Med 2007 — Reference physiological review.
- Pittas AG. et al. NEJM 2019 — D2d trial: effect on progression to diabetes in prediabetics (nuanced results).
Scoreboards and tracking
- 25-OH-D serum: Standard marker. Deficiency/insufficiency/sufficiency ranges according to laboratory.
- Calcium and PTH: useful for context and security.
- Re-evaluate 8-12 weeks after starting or changing the dose.
Warning: This content is for informational and educational purposes only, based on available scientific literature. It does not constitute medical advice and does not replace consultation with a healthcare professional. Claims regarding supplements have not been evaluated by the FDA or COFEPRIS to diagnose, treat, cure, or prevent any disease. Consult your doctor before starting any supplement, especially if you are pregnant, breastfeeding, under 18 years of age, or taking medication.
What we audit
In the vitamin D category, the relevant differences between brands lie not so much in the ingredient (cholecalciferol is a well-characterized molecule) as in the declared dose vs. actual dose, the chemical form, the excipients and the presence of cofactors.
Quality criteria
- Shape: We prefer D3 (cholecalciferol) over D2 (ergocalciferol) because of its greater effectiveness in raising 25-OH-D.
- Verifiable dose: Clear UI labeling per take and, ideally, third-party verification.
- Vehicle: Oily or fatty presentations improve absorption compared to dry powders.
- Cofactors: Formulas with K2 (MK-7) make physiological sense to direct calcium to bone.
- Purity: absence of unnecessary additives and stability controls.
Warning signs
- Products that do not specify whether the vitamin is D2 or D3.
- Extremely high doses marketed for daily use without analytical control warning.
- Unjustified mixtures with megadoses of calcium.
How to choose
For most people, a single, well-dosed vitamin D3 (alone or with potassium) meets the target. The choice of dosage should be guided by 25-OH-D blood tests and, where applicable, by professional judgment. Specific brand recommendations by country are linked from the offers associated with this molecule.
General protocol
- Maintenance: 1000-2000 IU/day of D3, with a meal containing fat to improve absorption.
- Deficit correction: Higher doses guided by 25-OH-D analysis and under professional judgment; re-evaluation at 8-12 weeks.
- Time of day: indifferent; prioritizes consistency and taking it along with fat.
Synergies
- Vitamin K2 (MK-7): It helps direct calcium towards the bone and not towards soft tissues.
- Magnesium: cofactor of vitamin D metabolism; its deficiency limits its effectiveness.
Precautions
- Hypercalcemia, sarcoidosis or granulomatous diseases: use only under medical supervision.
- Kidney disease or a history of calcium stones: requires supervision.
- Avoid sustained daily megadoses without analytical monitoring due to the risk of toxicity.
Evaluation window
The goal is to maintain an optimal and stable level of 25-OH-D. Changes in blood tests are measurable in 8-12 weeks; subjective benefits (energy, mood, reduced frequency of infections) are more variable and depend on the starting point.
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