NutriStack
Chlorthalidone and Vitamin D2, a caution.
Chlorthalidone reduces urinary calcium excretion, and Vitamin D2 can increase calcium absorption after metabolic activation. High-dose Vitamin D2 can therefore add to chlorthalidone's calcium-retaining effect. The concern is greatest when calcium supplements are also used or when kidney disease, hyperparathyroidism, granulomatous disease, or dehydration is present.
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
- Chlorthalidone and Vitamin D2
- Pair type
- Caution
- Evidence (highest tier)
- Emerging
- Source citations
- 2 sources
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Emerging evidence
Caution
What is happening. Chlorthalidone reduces urinary calcium excretion, and Vitamin D2 can increase calcium absorption after metabolic activation. High-dose Vitamin D2 can therefore add to chlorthalidone's calcium-retaining effect. The concern is greatest when calcium supplements are also used or when kidney disease, hyperparathyroidism, granulomatous disease, or dehydration is present.
Mechanism. Chlorthalidone has thiazide-like effects that increase distal calcium reabsorption. Vitamin D2 repletion increases intestinal calcium absorption, creating an additive hypercalcemia mechanism.
Recommendation. Avoid high-dose Vitamin D2 with chlorthalidone unless your clinician is tracking calcium. If Vitamin D2 is prescribed, ask when to recheck serum calcium and whether your calcium supplement dose should be adjusted.
Sources (2)
- Wermers RA, Kearns AE, Jenkins GD, Melton LJ 3rd. Incidence and clinical spectrum of thiazide-associated hypercalcemia. Am J Med. 2007;120(10):911.e9-911.e15. PMID 17904464
- Chandler PD, Scott JB, Drake BF, Ng K, Forman JP, Chan AT, et al. Risk of hypercalcemia in blacks taking hydrochlorothiazide and vitamin D. Am J Med. 2014;127(8):772-778. PMID 24657333
Stack Score
How this pair moves the number.
Effect on the composite score
If both Chlorthalidone and Vitamin D2 are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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