NutriStack
Alendronate and Calcium, timing-sensitive.
Calcium chelates alendronate and dramatically reduces its already-low bioavailability (0.6-0.7%). Taking calcium within 30 minutes of alendronate can render the bisphosphonate completely ineffective for osteoporosis treatment. However, calcium supplementation at a different time is recommended for bone health.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
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What the row says.
Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.
At a glance
- Substances
- Alendronate and Calcium
- 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 × Prescription
- Last verified
- May 30, 2026
Timing Sensitive · Strong evidence
Timing Sensitive
What is happening. Calcium chelates alendronate and dramatically reduces its already-low bioavailability (0.6-0.7%). Taking calcium within 30 minutes of alendronate can render the bisphosphonate completely ineffective for osteoporosis treatment. However, calcium supplementation at a different time is recommended for bone health.
Mechanism. Calcium cations chelate alendronate's bisphosphonate groups, forming insoluble calcium-bisphosphonate complexes. Since alendronate's baseline oral bioavailability is already less than 1%, even small reductions from chelation can eliminate therapeutic drug levels entirely.
Recommendation. Take alendronate first thing in the morning with plain water, at least 30 minutes before any food, beverages, or supplements including calcium. Take calcium supplements later in the day, at least 30 minutes after alendronate.
Minimum separation. 30
Sources (3)
- Gertz BJ et al. Studies of the oral bioavailability of alendronate. Clin Pharmacol Ther. 1995;58(3):288-298. PMID 7554702
- Liu C, Kuang X, Li K, Guo X, Deng Q, Li D. Effects of combined calcium and vitamin D supplementation on osteoporosis in postmenopausal women: a systematic review and meta-analysis of randomized controlled trials. Food & Function. 2020. PMID 33237064
- Yao P, Bennett D, Mafham M et al.. Vitamin D and Calcium for the Prevention of Fracture: A Systematic Review and Meta-analysis. JAMA Network Open. 2019. PMID 31860103
Stack Score
How this pair moves the number.
Effect on the composite score
If both Alendronate and Calcium 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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