Iron, calcium, sodium…..these are all minerals which an endurance athlete might consider when thinking about their nutrition. Am I getting enough iron in my diet to help prevent fatigue? Am I eating enough calcium to protect my bones? Am I replacing the sodium that I lose when I sweat? But do you ever think about whether you have adequate magnesium?

Magnesium is a mineral that plays a critical role in over 300 enzymatic processes in your body and is required by virtually every cell. Several functions are of particular interest to the endurance athlete. Magnesium is vital for the conversion of muscle glycogen to glucose, your body’s fuel during intense exercise, as it is needed to generate ATP (adenosine triphosphate). A lack of magnesium can lead to lactic acid build up, resulting in muscle soreness and fatigue. Along with calcium, magnesium is needed for muscle contraction and relaxation, and also for protein synthesis. Having sufficient magnesium can help to promote quick recovery. Magnesium also activates the enzymes that enable the body to convert vitamin D to its active form, which in turn enables calcium absorption for bone building. Other roles for magnesium include nerve function, blood pressure regulation, synthesis of fats and nucleic acids, and immune function. Magnesium stores are found in the bones, muscles, blood and other body fluids, and during exercise these stores are redistributed in order to meet your body’s metabolic needs for energy production, muscle function, nerve function, etc.

The recommended daily amount of magnesium is 300mg for men and 270mg for women. But these are based on the average population. Endurance athletes may have higher requirements as they produce more energy, use their muscles more, put a greater stress on their bones and sweat more, therefore losing higher amounts of magnesium (an electrolyte) as they do so. But does this mean that you need to take a magnesium supplement? Studies suggest that magnesium supplementation only has a benefit on exercise performance in individuals who are magnesium deficient. Magnesium supplementation of physically active individuals with adequate magnesium status has not been shown to enhance physical performance.1 

magnesium a guide for the endurance athleteTo ensure sufficient magnesium levels, start with your diet. I think of magnesium as the ‘vegan nutrient’. It is mostly found in plant foods, where it is one of the components of chlorophyll. To ensure that you are meeting your daily magnesium requirements, you need to include a selection of the following foods in your diet:

Food                                       Serving Size             Mg/serving size

Pumpkin seeds                    30g (2 tbsp)               160mg

Almonds                                30g (2 tbsp)               90mg

Wholegrain bread                100g (2 slices)          85mg

Beans or lentils                    200g (cooked)           80mg

Cashew nuts                        30g (2 tbsp)               83mg

Rice                                        75g                             82mg

Brazil nuts                             30g (2 tbsp)               68mg

Spinach                                 80g                             64mg

Sesame seeds                      30g (2 tbsp)               60mg

Peanuts                                 30g (2 tbsp)               55mg

Baked potato                         200g                           50mg

Walnuts                                 30g (2 tbsp)               48mg

Banana                                  120g                           35mg

Broccoli                                  80g                             24mg

If you are not including leafy greens, beans and lentils, and nuts and seeds in your diet, now would be a good time to start if you experience fatigue, poor recovery, or muscle soreness or cramping. A magnesium deficiency could be at the root of your issues. Dietary surveys suggest that magnesium deficiency is quite common, given the common reliance on processed foods and also a decline in the amount of magnesium found in soil over the past 50 years, affecting the amount in natural foods 2. Deficiency may be even more likely in athletes with higher magnesium requirements. As well as a lack of dietary sources of magnesium, if you consume soda-type drinks, this could be another contributing factor to deficiency, as the phosphorus in the drinks binds to magnesium and makes it unavailable for use in your body. Reducing your intake of highly processed and refined foods, which lose magnesium during processing, and replacing these with ‘real foods’ (including those on the list above) may also be helpful.

If you do decide to supplement with magnesium, choose a form that is well absorbed like magnesium citrate, magnesium malate or magnesium glycinate. Some multi-vitamin and mineral products aimed at athletes contain the full RDA or more for magnesium, so this is another option. I would avoid supplementing more than 400mg per day as your diet will also contribute some magnesium. Taking too much could result in loose stools. If you experience muscle soreness after exercise and find it hard to recover quickly enough, it may be worth trying a form of magnesium that you spray onto the affected areas, eg your legs, or use in a flake form in a bath. Magnesium supplementation appears to work well in a ‘transdermal’ form like this, by which it is quickly absorbed through the skin. One brand to try, if you are in the UK, is Better You. They sell spray-on oil and magnesium chloride flakes for use in a bath. Visit for more details.

In summary, magnesium is a nutrient that you need to be aware of as an endurance athlete. I hope you find the information in this blog helpful.

Jo Scott-Dalgleish BSc (Hons) is a BANT Registered Nutritionist, writing and giving talks about nutrition for endurance sportBased in London, she also works as a Registered Nutritional Therapist, conducting onetoone consultations with triathletes, distance runners and cyclists to help them eat well, be healthy and perform better through the creation of an individual nutritional plan. To learn more about these consultations, please visit



1 Nielsen FH & Lukaski HC. Update on the relationship between magnesium and exercise. Magnes Res. 2006. 19 (3): 180-9

2 Davis DR, Epp MD & Riordan HD. Changes in USDA food composition data for 43 garden crops, 1950 to 1999. J Am Coll Nutr. 2004. 23(6): 669-82