Calcium Carbonate vs. Calcium Ascorbate
Among 5,062 on-market calcium products with an identifiable primary form, 47.2% use Calcium Carbonate (2,391 products) and 8.3% use Calcium Ascorbate (418).
| Calcium Carbonate | Calcium Ascorbate | |
|---|---|---|
| Quality tier | Tier 2 | Unrated |
| Calcium by weight | 40.0% | 9.4% |
| Share of market | 47.2% | 8.3% |
| On-market products | 2,391 | 418 |
| Median declared dose | 130 elemental mg middle half: 50–300 | 56 elemental mg middle half: 29–108 |
| Most common brands | Wonder Laboratories, DC, 21st Century | MH Michael's Health Naturopathic Programs, American Health, NOW |
Doses are declared per serving in elemental mg. “By weight” is the share of the ingredient that is the nutrient itself (e.g. elemental magnesium in a magnesium salt).
Why Calcium Carbonate is tier 2
Absorption from calcium citrate was 20-27% higher than from carbonate in a meta-analysis (15 studies, 184 subjects; Sakhaee 1999), i.e. carbonate absorbed roughly 17-21% less; carbonate absorption is better with meals/gastric acid (general pharmacology, not from the abstract).
Source: Sakhaee K et al. 1999, Am J Ther 6(6):313-321, PMID 11329115
Why Calcium Ascorbate is unrated
Used primarily as a buffered vitamin C source; no calcium-specific bioavailability study was found.
Source: none located (no calcium-specific bioavailability study found)