When to take magnesium for runners?

The habit, the rule, and why the rule matters more to a runner than to anyone else

When to take magnesium for runners has the same answer as for every reader on this site, with one rule that matters more to a runner than to anyone else. The habit: with the evening meal, every day, as bisglycinate at 300mg elemental where a diet audit finds intake short, because magnesium works by status built over weeks of daily intake rather than by a dose before or after a run, and the evening meal is the fixed point a runner's day keeps whatever the training plan says, the runners' form page's recommendation restated as a time. The rule: never before a run. Magnesium's laxative effect is osmotic and arrives within hours of a dose, citrate and oxide carrying more of it and bisglycinate the least, and a runner who takes a citrate with breakfast and heads out for a long run has arranged for the effect to arrive at mile eight with no bathroom in sight, the runner's trots being a recognised affliction that magnesium salts can provoke and that the evening habit avoids entirely, so the rule for a runner is not merely a preference for the evening but a prohibition on the morning of a run, and a prohibition on citrate and oxide at any hour a run follows. The sweat question answers itself once the rule is set: runners lose more magnesium in sweat than lifters, long runs in heat losing the most, and the losses are still tens of milligrams a session on the sweat page's arithmetic, replaced by meals and by the daily habit without any post-run window, the after-run capsule being the evening capsule taken at that anchor and nothing more.

Race week, the cramp question runners always ask, and the runner's timing filed

Race week changes nothing about the magnesium habit and adds one rule that governs every supplement: nothing new starts on race day, or in race week, the honest principle that a runner races on the routine that trained them, so a runner who has taken bisglycinate at dinner for months keeps doing so through race week including the night before, and a runner who has not does not start on the Friday, a new supplement being an unrehearsed gut on race morning. The cramp question runners always ask belongs here because it drives the timing question: exercise-associated cramps are, on the sports medicine literature, more about neuromuscular fatigue than about magnesium, the Cochrane review finding magnesium unlikely to help ordinary cramps, and the cramp that arrives at mile twenty is a pacing, conditioning and fatigue problem before it is a mineral one, so a runner takes magnesium for its lawful muscle-function and fatigue claims where their diet runs light and does not time it against a cramp it has not been shown to prevent, hydration and electrolytes on long hot runs being the pre-race levers with evidence. The runner's timing filed: bisglycinate at 300mg elemental with the evening meal every day of the plan, never before a run and never as citrate or oxide on a running day, race week unchanged and nothing new on race day, sweat losses replaced by meals, and cramps handled by conditioning and hydration rather than by a magnesium clock, the worked example being the salt that stays off the trail, two capsules with dinner, 300mg at 80% NRV, £19.99 for 90 days at 22p.

The verdict, dinner every day and never the morning of a run

When to take magnesium for runners: with the evening meal every day, as bisglycinate at 300mg elemental where a diet audit finds intake short, because status over weeks is the mechanism and dinner is the anchor a runner keeps, and never before a run, a laxative salt on a running morning being the trots waiting at mile eight, with sweat losses replaced by meals, race week unchanged and nothing new started on race day, and cramps handled by pacing, conditioning and hydration rather than a magnesium clock. The runner's evening habit: Futuro Labs Magnesium Glycinate, two capsules with dinner, 300mg elemental at 80% NRV, £19.99 for 90 days at 22p a day.

What to check on the label

Questions people also ask

Should runners take magnesium before a run?

No: magnesium's laxative effect is osmotic and arrives within hours, citrate and oxide carrying most of it, so a morning dose before a long run risks the runner's trots mid-run, and the evening meal is the runner's anchor.

Do runners need more magnesium than other people?

A little: sweat losses on long runs, especially in heat, are higher than a lifter's but still tens of milligrams a session, replaced by meals and a daily habit rather than by any post-run dose.

Should I take magnesium the night before a race?

Only if you have been taking it for months: race week changes nothing about an established evening habit, and nothing new starts in race week or on race day, an unrehearsed supplement being an unrehearsed gut.

Does magnesium stop running cramps?

Unlikely: the Cochrane review found magnesium unlikely to help ordinary cramps, and exercise-associated cramps are more about neuromuscular fatigue, pacing and conditioning, with hydration and electrolytes on long hot runs the pre-race levers with evidence.

Which magnesium is best for runners?

Bisglycinate: well absorbed, the least laxative of the common salts and therefore the one that stays off the trail, at 300mg elemental with the evening meal.

Sources

1. Maughan RJ, Shirreffs SM. Muscle cramping during exercise: causes, solutions, and questions remaining. Sports Medicine 2019;49(Suppl 2):115-124. PubMed record
2. Schwellnus MP. Cause of exercise associated muscle cramps (EAMC): altered neuromuscular control, dehydration or electrolyte depletion? British Journal of Sports Medicine 2009;43(6):401-408. https://pubmed.ncbi.nlm.nih.gov/18981039/
3. Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews 2020, Issue 9, CD009402. PubMed record
4. Lukaski HC. Magnesium, zinc, and chromium nutriture and physical activity. American Journal of Clinical Nutrition 2000;72(2 Suppl):585S-593S. PubMed record

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