NutriStack
Calcium and Vitamin D2, timing-sensitive.
Vitamin D2 increases how much dietary and supplemental calcium the gut absorbs, which is beneficial for bone health at sensible doses but can become problematic when both are taken in large amounts together, raising the risk of hypercalcemia and kidney stones.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
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What the row says.
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At a glance
- Substances
- Calcium and Vitamin D2
- Pair type
- Timing Sensitive
- Evidence (highest tier)
- Strong
- Source citations
- 3 sources
- Stack Score effect
- −5 to your Stack Score (per scored timing-sensitive row).
- Scope
- Supplement × Supplement
- Last verified
- May 30, 2026
Timing Sensitive · Strong evidence
Timing Sensitive
What is happening. Vitamin D2 increases how much dietary and supplemental calcium the gut absorbs, which is beneficial for bone health at sensible doses but can become problematic when both are taken in large amounts together, raising the risk of hypercalcemia and kidney stones.
Mechanism. Active vitamin D, produced from supplemental ergocalciferol (D2), upregulates intestinal calcium absorption by inducing the transient receptor potential channel TRPV6 and the binding protein calbindin in enterocytes, and it also increases renal calcium reabsorption. This is the intended physiological synergy for bone health, but it means high-dose D2 amplifies how much supplemental calcium is absorbed. At supraphysiologic combined intakes the additive effect can push serum calcium upward, with documented risk of hypercalcemia, hypercalciuria, and kidney stones.
Recommendation. Pairing modest doses is appropriate for bone health: keep total supplemental calcium around 500 to 1000 mg/day (split into 500 mg doses with food for absorption) alongside standard D2 dosing. Avoid combining high-dose D2 with high-dose calcium without monitoring. Anyone on large D2 doses plus calcium, or with a history of kidney stones, hyperparathyroidism, or sarcoidosis, should have serum and urinary calcium checked periodically. Watch for nausea, excessive thirst, frequent urination, or confusion as signs of hypercalcemia.
Minimum separation. No separation needed; taking together with food actually aids calcium absorption. The concern is total combined dose, not timing.
Sources (3)
- Christakos S, et al. Vitamin D: Metabolism, Molecular Mechanism of Action, and Pleiotropic Effects. Physiol Rev. 2016. PMID 26681795
- Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. . 2011. PMID 21796828
- National Institutes of Health, Office of Dietary Supplements. Calcium and Vitamin D Fact Sheets for Health Professionals.
Stack Score
How this pair moves the number.
Effect on the composite score
If both Calcium and Vitamin D2 are in the same stack, this pair applies −5 to your Stack Score (per scored timing-sensitive row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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