Research statusCatalogued record, not clinically approved.
Citation presence and an automated evidence check are not medical review.
This pair has not completed NutriStack's standalone publication gate. Attached sources may mention one or both substances without establishing the stored interaction type, direction, severity, dose, management advice, or combined safety. The page is excluded from search indexing and must not be used to start, stop, or change treatment.
From the databaseWhat the row says.
Every entry follows the same shape: what is happening, the mechanism, and the recommendation.
Pair type
Timing Sensitive
Scope
Supplement × Prescription
Last updated
July 13, 2026
Timing SensitiveStrong evidence
What is happening. Calcium supplements significantly reduce levothyroxine absorption by 20-25% through chelation in the gastrointestinal tract. This can lead to subtherapeutic thyroid hormone levels, worsening hypothyroid symptoms, and the need for dose adjustments. The interaction is well-documented in multiple controlled studies.
Mechanism. Calcium cations form insoluble chelate complexes with levothyroxine in the acidic environment of the stomach, preventing absorption across the intestinal mucosa. The calcium-thyroxine complex is excreted in the feces.
Recommendation. Separate levothyroxine and calcium by at least 4 hours. Take levothyroxine on an empty stomach in the morning, and calcium later in the day. Have TSH monitored when starting or stopping calcium supplements.
Direction. Calcium changes how Levothyroxine behaves.
TimingTiming & separation.
The stored record proposes this minimum window. Confirm medication schedules with a clinician or pharmacist.
Stack Score
How it moves the number.
Effect on the composite score
No numeric score interpretation is published for this unreviewed pair record.
Stack Score is a NutriStack product heuristic, not a clinical risk or benefit grade. An unreviewed database label must not be treated as a safety or benefit signal. The algorithm is documented at /methodology/stack-score.
SourcesSources, by evidence tier.
Sources attached to the record. Some support an ingredient or mechanism rather than a study of the exact pair; PMIDs link to PubMed where available.
Reference material
5- 1Singh N et al. Effect of calcium carbonate on the absorption of levothyroxine. JAMA. 2000;283(21):2822-2825.Source linkedPMID
- 2Zamfirescu I, Carlson HE. Absorption of levothyroxine when coadministered with various calcium formulations. Thyroid. 2011;21(5):483-486.Source linkedPMID
- 3Ross DS. Treating hypothyroidism is not always easy: When to treat subclinical hypothyroidism, TSH goals in the elderly, and alternatives to levothyroxine monotherapy. Journal of Internal Medicine. 2022.Source linkedPMID
- 4Liu 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.Source linkedPMID
- 5Yao 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.Source linkedPMID
FAQCommon Calcium + Levothyroxine questions.
Plain-language answers drawn from the interaction record on this page.
Can I take Calcium and Levothyroxine together?
NutriStack flags a possible timing issue between Calcium and Levothyroxine. Confirm the right schedule with a clinician or pharmacist. Calcium supplements significantly reduce levothyroxine absorption by 20-25% through chelation in the gastrointestinal tract. This can lead to subtherapeutic thyroid hormone levels, worsening hypothyroid symptoms, and the need for dose adjustments. The interaction is well-documented in multiple controlled studies.
What kind of interaction is it?
Timing-sensitive: the stored record proposes separating the substances; confirm the interval for your regimen with a clinician or pharmacist.
How does this affect a NutriStack Stack Score?
No numeric score interpretation is published for this pair because its stored label has not completed source-level clinical review.
What do the cited sources establish?
NutriStack lists 5 source records with this Calcium + Levothyroxine entry. A source may support an ingredient, mechanism, or safety concern without testing the exact pair, so citation presence alone does not prove the visible verdict. Full sourcing methodology is at https://nutristackapp.com/methodology/interactions.
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