A systematic review of 128 mineral and trace-element supplement studies in healthy adults, most of them rated moderate in quality, found little evidence that mineral supplements improve performance outside particular situations such as a deficiency or heat: there was no evidence that magnesium improves endurance performance, the magnesium gains in jump height, one-rep max and fatigue resistance come from two single trials, and the nine zinc studies give little quality evidence of any performance effect. From the full text
Main caveat: No meta-analysis: each mineral is a narrative account of its studies, and the magnesium "possible exception" rests on single trials.
Heffernan and colleagues (University College Dublin and Dublin Institute of Technology) searched six databases and grey-literature sources between January and April 2018 for studies that gave minerals or trace elements as supplements to healthy people aged 17 or older, and kept 128 studies (130 experiments).
Two reviewers rated every study with the EPHPP quality tool: eight came out strong, 95 moderate and 25 weak, and only iron (six) and magnesium (two) had any study rated strong. The outcomes were too diverse to pool, so each mineral is discussed in turn.
Their overall verdict is that research backing mineral supplements for sport is short of both quantity and quality; iron, mainly when status is compromised, and magnesium have the most and the best studies.
For magnesium the authors found no evidence of better endurance performance; 300-500 mg a day for about one to four weeks went with better jump height in one study and better one-rep max and fatigue resistance in another. For zinc they found little quality evidence of a performance effect.
Beyond assessing baseline insufficiency and meeting the RDA, they found the evidence too thin for mineral-specific guidelines.
Participants
128 studies, 3643 participants (1387 women), aged 17-75; 24 studies in elite athletes.
Magnesium: 22 studies, 663 participants (72 women); 10 RCTs, 3 of them in elite athletes.
Zinc: 9 studies, 229 participants (50 women); 4 RCTs, 1 in elite athletes.
Iron 29 studies, calcium 11, phosphate 17, sodium 15, selenium 5, chromium 12, boron 5 (4 in the abstract), multi-mineral 5. No eligible study for copper, manganese, iodine, nickel, fluoride or cobalt.
Protocol
Search: MEDLINE, EMBASE, CINAHL, SPORTDiscus, Web of Science and clinicaltrials.gov, January-April 2018, plus hand-searched reference lists; 17,459 records (17,433 in the abstract), 14,144 after duplicates, 328 read in full, 128 included.
Eligibility: healthy adults and athletes aged 17 or older, both sexes, English language, supplement studies; interventional and controlled designs were the target, and the limitations section says cross-sectional studies were also kept. Excluded: animal and cell work, children, diseased groups in which a deficiency was part of the diagnosis, dietary-intake-only studies, and minerals combined with other molecules (such as ZMA).
Quality: EPHPP, rated independently by two reviewers with a third for disagreements; studies describing their athletes as trained or elite were graded "somewhat likely" for selection bias.
Synthesis: narrative, by mineral; no meta-analysis because the outcome measures varied too widely.
Funding and interests: no external funding; the lead author declares grant funding from Marigot Ltd; the other authors declare none.
Key Results
| Mineral | Studies (participants; RCTs) | The authors' performance verdict (full text) |
|---|---|---|
| Magnesium | 22 (663; 10) | No evidence of better endurance performance. 300-500 mg a day for about 1-4 weeks was linked with better countermovement jump, one-rep max and fatigue resistance, and with no change in isokinetic strength; about 7 weeks of 8 mg/kg a day with lower-body resistance training raised strength in previously untrained people. |
| Zinc | 9 (229; 4) | Little quality evidence of a performance effect; trials ran 1-6 weeks. |
| Iron | 29 (946; 19) | The most and the best-rated research (six studies strong); benefit mainly when iron status is compromised, for example 15-60 mg a day of elemental iron for six to eight weeks in non-anaemic iron-deficient women. |
| Phosphate | 17 (247; 13) | Several ergogenic effects of about 4 g a day of sodium phosphate for 3-6 days, limited to highly trained people. |
| Sodium | 15 (387; 5) | No clear effect in healthy competitive endurance athletes in temperate conditions; some evidence for a 164 mmol/L drink before exercise in the heat. |
| Calcium, selenium, chromium, boron | 11, 5, 12, 5 | No performance benefit shown. |
| Multi-mineral | 5 (152; 3) | Little evidence; one sodium-potassium-magnesium loading study in half-ironman racing awaits replication. |
Magnesium, the studies behind the verdict: in elite volleyball players, 350 mg a day for four weeks improved countermovement jump by about 6% against placebo, with no difference in isokinetic dynamometry.In 13 recreational endurance athletes already eating about 370 mg a day, one week at 300 mg a day raised bench-press one-rep max by 17% against their own pre-supplement value (not against placebo), while four weeks did not change it.In a marathon trial, 365 mg a day changed neither muscle or serum magnesium nor marathon performance against placebo; in athletes with low-normal serum magnesium, 500 mg a day for three weeks changed neither magnesium concentrations nor aerobic capacity.
Zinc, the studies behind the verdict: six weeks of 30 mg a day of zinc gluconate raised an estimated (not measured) VO2peak in female futsal players; two weeks of 70 mg a day of zinc carnosine did not change a ride at 80% of VO2peak; one week of 20 mg a day did not change estimated VO2peak in sedentary men. The authors note that the VO2peak values were estimates.
Overall: the authors find the evidence for mineral supplements in sport lacking in volume and quality, see iron and magnesium as possible exceptions in particular situations (deficiency, heat and so on) rather than as general ergogenic aids, and recommend assessing baseline insufficiency and meeting the RDA; there are no athlete-specific guidelines.
Practical Application
For a healthy athlete, magnesium and zinc supplements are unproven for performance: across 128 supplement studies in adults (24 in elite athletes), the authors found no evidence that magnesium improves endurance performance and little quality evidence for zinc; they call magnesium a possible exception, but its gains in jump height, one-rep max and fatigue resistance rest on two single trials, one of them in 13 athletes. Check the diet and, where there is a reason, the blood status first; a measured deficiency is a separate question for a doctor (SYNTH-97 for iron).
If an athlete wants to try magnesium for strength or jump, say what it rests on: one trial for jump; for strength, one trial in athletes plus a 7-week trial in previously untrained people who also did resistance training (other trials found no change in isometric or isokinetic strength); and the 17% one-rep-max gain was measured against the group's own starting value, not against placebo. It is unproven, not shown to work.
Zinc bought "for immunity" is a question about colds, not performance; this review does not answer it.
Limitations
No meta-analysis: each mineral is a narrative account of its studies, and the magnesium "possible exception" rests on single trials.
Mixed designs: controlled trials and cross-sectional studies sit side by side; only 10 of 22 magnesium and 4 of 9 zinc studies were RCTs.
Short trials: most magnesium and zinc trials described ran one to seven weeks; the zinc VO2peak values were estimated.
The search ended in April 2018 and was limited to English.
The text has small inconsistencies: 17,459 records in the Results against 17,433 in the abstract, five boron studies against four, and a calcium paragraph that reports 11 studies but "19 RCTs".
The lead author declares grant funding from a company (Marigot Ltd).
The per-study supplementary table was not read; the doses and forms of magnesium and zinc beyond those quoted above are not given here.
How this entry was checked and changed
Why this level
a systematic review whose risk of bias was read in the full text (EPHPP global rating: 8 of 128 studies strong, 95 moderate, 25 weak); A- rather than A because the studies are mostly small and moderate in quality, the designs are mixed (10 of the 22 magnesium studies and 4 of the 9 zinc studies were RCTs), the outcomes were too varied to pool, and each positive magnesium finding rests on one trial