Magnesium in the Blood Above or Below Normal: Causes in Athletes and What to Do
Magnesium outside the reference interval is a result that requires attention, since this mineral affects the muscles, nerves and heart rhythm. The editorial team examines why magnesium in the blood of athletes decreases or rises, which causes are the most common and what to do after receiving such a report.
The limits of normal and what counts as a deviation
The reference interval for total serum magnesium in most laboratories is approximately 0.70–1.0 mmol/L, although the specific limits depend on the method. Values below the lower limit are described as hypomagnesemia, and above the upper limit as hypermagnesemia.
Some experts, in particular the authors of the review by Costello et al. (2016), believe that results between 0.75 and 0.85 mmol/L may already indicate an insufficient status. For an athlete with symptoms this is a reason to assess the diet and losses more carefully, even if the level is formally "within normal".
Since the serum contains less than 1% of the body's total magnesium, a reduced result usually means that the deficiency is already quite pronounced or the losses are significant. An elevated result, on the contrary, is most often associated with impaired kidney function or with a laboratory artifact.
Before looking for a cause, it is worth ruling out technical errors: hemolysis of the sample falsely raises magnesium, and low albumin lowers the total fraction.
Causes of low magnesium in athletes
Hypomagnesemia develops when intake does not cover losses or when magnesium moves from the blood into the cells. Below are the most common causes, grouped by mechanism.
| Mechanism | Examples | Comment for the athlete |
|---|---|---|
| Low intake | A diet without whole grains, nuts or legumes; strict diets | Common with weight control and "cutting" |
| Intestinal losses | Diarrhea, malabsorption, laxative abuse | Occurs with GI disorders during competitions |
| Renal losses | Loop and thiazide diuretics, alcohol, some antibiotics and antitumor agents | Diuretics as a means of "cutting weight" are a separate risk |
| Proton pump inhibitors | Long-term use | In 2011 the FDA warned of the risk of hypomagnesemia |
| Shift into the cells | Insulin administration, refeeding syndrome | Relevant after prolonged fasting |
| Losses through sweat | Prolonged loads in the heat | The contribution is moderate but adds up with others |
Separately, the editorial team draws attention to diuretics. In sports they are banned by the World Anti-Doping Agency as masking agents, and their use for rapid weight loss before weigh-in threatens severe electrolyte disturbances, including hypomagnesemia and hypokalemia.
The manifestations of deficiency are nonspecific: cramps and muscle twitching, tremor, weakness, fatigue, heart rhythm disturbances. Low magnesium is often accompanied by low potassium and calcium, which cannot be raised without correcting magnesium.
Intense training immediately before the test can temporarily lower serum magnesium due to its redistribution, so it is best to give blood after a rest day.
Causes of high magnesium
Healthy kidneys efficiently excrete excess magnesium, so clinically significant hypermagnesemia in people with normal kidney function is rare. Most often it combines two factors: reduced kidney function and excessive intake.
- renal failure of any origin, including acute kidney injury after severe rhabdomyolysis or dehydration;
- high doses of magnesium-containing laxatives and antacids;
- large doses of magnesium supplements, especially in kidney diseases;
- intravenous administration of magnesium in medical settings;
- a laboratory artifact due to hemolysis of the sample.
The US Institute of Medicine has set for adults an upper tolerable limit for magnesium specifically from supplements and medications — 350 mg per day. It applies not to food but to additional intake; exceeding it often manifests as diarrhea, especially when taking magnesium oxide or citrate.
The signs of pronounced hypermagnesemia are nausea, weakness, lowered blood pressure, a slowed pulse, suppression of reflexes, drowsiness and, in severe cases, disturbances of breathing and heart rhythm. Such conditions require emergency medical care.
For an athlete whose magnesium turned out to be moderately elevated against a background of supplements, the first step is usually to check creatinine and retake the test without hemolysis.
What to do in case of a deviation
The algorithm of action begins with confirmation: retake the test fasting, after a rest day, without magnesium supplements on the day of the draw. Together with magnesium it is useful to determine potassium, calcium, albumin and creatinine.
In case of confirmed low magnesium, the doctor looks for the cause: reviews medications (PPIs, diuretics), assesses intestinal function, alcohol consumption and the diet. A mild deficiency is often corrected with nutrition and oral supplements, while a pronounced one or one with rhythm disturbances is treated in a medical setting.
From a nutritional standpoint, it is worth increasing the share of whole-grain products, nuts, pumpkin seeds, legumes, leafy greens and cocoa. Among supplements, forms with better tolerability, such as glycinate or citrate, are usually chosen for daily intake, keeping to the upper limit of 350 mg of magnesium from supplements without a doctor's prescription.
In case of confirmed high magnesium, the intake of all magnesium-containing products is stopped and kidney function is necessarily assessed. You should not "flush out" magnesium on your own.
Editorial conclusions
Low magnesium in athletes is most often associated with the diet, diarrhea, the use of PPIs or diuretics and large fluid losses. High magnesium is almost always associated with a combination of supplements or laxatives and reduced kidney function, or with hemolysis of the sample.
Any deviation should be confirmed with a repeat test and assessed together with potassium, calcium, albumin and creatinine.
Correction is carried out through the diet and moderate doses of supplements within the safe level, and in case of pronounced deviations — only under a doctor's supervision.
We also recommend reading our materials on what the magnesium blood test shows, on vitamin D above or below normal and on vitamin B12 deviations.
References
- de Baaij JH, Hoenderop JG, Bindels RJ. Magnesium in man: implications for health and disease. Physiol Rev. 2015;95(1):1–46.
- Costello RB, Elin RJ, Rosanoff A, et al. Perspective: the case for an evidence-based reference interval for serum magnesium: the time has come. Adv Nutr. 2016;7(6):977–993.
- Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press; 1997.
- U.S. Food and Drug Administration. Low magnesium levels can be associated with long-term use of proton pump inhibitor drugs (PPIs): FDA Drug Safety Communication. 2011.
- Hoorn EJ, van der Hoek J, de Man RA, et al. A case series of proton pump inhibitor-induced hypomagnesemia. Am J Kidney Dis. 2010;56(1):112–116.
- Nielsen FH, Lukaski HC. Update on the relationship between magnesium and exercise. Magnes Res. 2006;19(3):180–189.
- World Anti-Doping Agency. The World Anti-Doping Code International Standard: Prohibited List. Montreal: WADA; current edition.
Andriy Melnyk
A strength-sports coach and author of programs for beginner and intermediate levels. Writes about training planning.
