Calcium + Magnesium — Supplement Stacking Guide

References

1. A dose-response study in 21 healthy adults (4 men, 17 women, aged 22–60) compared intestinal calcium absorption from calcium carbonate and calcium citrate at 0.5, 1.0 and 2.0 g of elemental calcium, with a subset also tested at 0.2 g, using the rise in urinary calcium after an oral calcium load as the absorption marker. Absorption rose steeply from 0 to 0.5 g with only slight further increase up to 2.0 g, leading the authors to identify roughly 0.5 g per dose as the point of diminishing return for either salt. The urinary calcium increment was higher from calcium citrate than from calcium carbonate at all four dose levels, and the authors concluded that the results confirm greater calcium bioavailability from citrate than from carbonate. PubMed
2. In a four-way crossover trial, 14 healthy adult women received placebo or 1200 mg of calcium as carbonate, citrate, or formate after an overnight fast, with serum calcium tracked for 270 minutes. The serum calcium response to calcium carbonate did not differ significantly from placebo (area under the curve 91 vs 107 mg·min/dl). Calcium citrate produced a modestly but significantly greater response than either (178 mg·min/dl), and calcium formate — an experimental form not in general supplement use — produced the largest response (378 mg·min/dl). These are short-term serum measurements in a small fasted sample and were not designed to assess bone or long-term outcomes. PubMed
3. In a two-year randomized, double-blind dose-response trial in pubertal adolescents — with vitamin D held constant across all groups — higher calcium intake was shown to produce greater hip bone mineral density accretion in girls, supporting bone development. PubMed
4. In an 18-month randomized controlled trial of 96 adolescent girls with low dietary calcium, calcium supplementation was shown to increase gains in bone mineral density and content during the supplementation period, supporting bone mineralization (the effect was not sustained after supplementation stopped). PubMed
5. Marketed calcium citrate and carbonate showed equivalent 24h absorption time-course in vitamin-D-replete postmenopausal women (n=24). PubMed
6. In a two-year randomized controlled trial of 122 healthy postmenopausal women, calcium supplementation was shown to slow the normal age-related decline in bone mineral density, supporting the maintenance of bone density. PubMed
7. A study reported that a microcrystalline hydroxyapatite compound supported positive calcium balance in the patients studied. PubMed
8. Systematic review of calcium-peptide/amino acid chelate formation and absorption: chelated calcium demonstrates superior GI stability and enhanced absorption vs inorganic calcium salts, with bioavailability advantages documented across in vitro and in vivo models due to distinct absorption pathways PubMed
9. Magnesium oxide showed relatively poor bioavailability (fractional absorption ~4%) in normal volunteers, while magnesium chloride, lactate, and aspartate showed significantly higher and equivalent absorption. PubMed
10. Increasing brain magnesium with magnesium-L-threonate enhanced learning, working memory, and short- and long-term memory in rats, accompanied by increased hippocampal synaptic density and enhanced synaptic plasticity. PubMed
11. In a double-blind, placebo-controlled study of 109 healthy Chinese adults, a magnesium L-threonate (Magtein PS) based formula at 2 g/day for 30 days significantly improved memory and overall memory quotient scores versus placebo, with greater improvement in older participants. PubMed
12. In sleep-restricted healthy subjects, 3 g of glycine taken before bedtime reduced subjective daytime sleepiness and fatigue, supporting glycine's independent sleep-related effects (relevant to magnesium glycinate's glycine co-molecule). PubMed
13. This review establishes magnesium as an essential intracellular cation involved in over 600 enzymatic reactions including energy metabolism and protein synthesis, with important physiological roles in the brain, heart, and skeletal systems. PubMed
14. A randomized, double-blind, placebo-controlled trial evaluated MMFS-01 (magnesium L-threonate) in older adults (age 50-70) with cognitive impairment for its ability to reverse cognitive impairment and improve sleep. PubMed
15. This review of the evidence concludes that the propagation of transdermal (topical) magnesium absorption is scientifically unsupported, in contrast to the well-documented effectiveness of oral magnesium supplementation. PubMed
16. An ex-vivo and double-blind crossover study in healthy subjects compared magnesium bioavailability of Sucrosomial® magnesium against magnesium citrate, oxide, and bisglycinate preparations. PubMed
17. This hypothesis paper argues that magnesium and taurine exert complementary actions to lower intracellular free calcium, providing a mechanistic rationale for magnesium taurate's proposed vascular-protective effects. PubMed
18. In a randomized, double-blind, placebo-controlled trial, adults with poor sleep who took magnesium (as bisglycinate) showed a modestly greater improvement in sleep quality than those taking a placebo, an effect that appeared greater in people with lower dietary magnesium intake. PubMed
19. A 2026 randomized, double-blind, placebo-controlled trial found that six weeks of magnesium L-threonate supplementation improved overall cognitive performance and reaction time in adults with self-reported sleep dissatisfaction, compared to placebo. PubMed
20. A 2024 randomized, double-blind, placebo-controlled trial found that adults with self-reported sleep problems who took magnesium L-threonate showed improved deep and REM sleep measures, along with better daytime mood, energy, and alertness, compared to placebo. PubMed
21. Comparative Clinical Study on Magnesium Absorption and Side Effects After Oral Intake of Microencapsulated Magnesium (MAGSHAPE(TM) Microcapsules) Versus Other Magnesium Sources. PubMed
22. A meta-analysis of small trials found older adults taking magnesium fell asleep roughly 17 minutes faster than those on placebo, though the authors rated the evidence as low quality and called for better-designed studies. PubMed
23. In adults with low magnesium levels and high stress, oral magnesium was associated with a substantial reduction in perceived stress over eight weeks, though the trial had no placebo group. PubMed
24. A 2003 randomized, double-blind, placebo-controlled parallel trial in 46 healthy individuals (300 mg elemental magnesium daily for 60 days) found that magnesium citrate and a magnesium amino-acid chelate, analysed together, showed greater absorption than magnesium oxide by 24-hour urinary magnesium; magnesium citrate alone produced the highest serum magnesium, and magnesium oxide did not differ from placebo. PubMed
25. A 1994 randomized crossover trial in patients with ileal resection (n=12) -- a population at elevated risk for magnesium malabsorption -- found no significant overall difference in magnesium absorption between magnesium diglycinate (chelate) and magnesium oxide, but found diglycinate was significantly better absorbed in the subset of patients with the most severe absorption impairment. PubMed
26. A 1990 controlled study found that magnesium citrate was substantially more soluble than magnesium oxide across a range of simulated gastric-acid conditions, and that magnesium absorption (measured by urinary magnesium rise after an oral dose) was significantly higher with magnesium citrate than with magnesium oxide. PubMed