Running challenges nearly every system in the body, from oxygen transport and energy metabolism to bone strength and muscle function. While macronutrients supply the energy to train and recover, micronutrients play key roles in supporting these processes efficiently.

Runners may be more prone to certain micronutrient deficiencies due to losses through sweat and impact, higher training loads, or dietary restrictions. This blog highlights five micronutrients particularly important for endurance athletes. 

Note: athletes should always consult with their healthcare provider or a registered dietitian prior to taking any supplementation.  

Iron 

Shortness of breath, fatigue, and decreased endurance are all problematic when your sport relies heavily on oxygen delivery and energy production. Iron supports both by facilitating oxygen transport in the blood and enabling energy generation within muscle cells. However, runners face unique challenges in maintaining adequate iron levels due to increased losses from sweat, gastrointestinal bleeding, and the repetitive impact that destroys red blood cells during foot strikes (see our blog “The Impact of Foot Strike Anemia”). Compounding these losses, intense or prolonged exercise temporarily raises hepcidin (a hormone that reduces iron absorption and recycling as part of the body’s inflammatory response) levels. This elevated hepcidin can last for several hours post-exercise, potentially limiting iron availability if dietary intake and recovery fall short. Collectively, these factors increase one’s risk of iron deficiency, which can impair endurance and delay recovery. 

Research shows that even iron deficiency without anemia can negatively affect performance, while iron deficiency anemia may lower VO2 max [1]. Runners should prioritize consuming adequate portions of iron-rich foods, especially heme iron sources, which are the most bioavailable. If supplementation is necessary, athletes should consult their healthcare provider or a registered dietitian. 

Magnesium

Magnesium plays a critical role in helping runners sustain performance and recover efficiently. It supports energy production, regulates muscle contractions, and facilitates nerve signaling. These functions become especially important during long-distance or high-intensity training.

Endurance athletes are more likely to have low magnesium status due to increased losses through sweat, elevated physiological demands, and common dietary gaps, particularly in those who don’t regularly consume nuts, seeds, legumes, whole grains, or leafy greens. Gastrointestinal issues, which are not uncommon in this population, can further impair magnesium absorption.

Recent research suggests that magnesium supplementation may reduce muscle soreness, accelerate post-run recovery, and help protect muscles from damage [2]. One mechanism behind this benefit is magnesium’s role in regulating calcium within muscle cells. When magnesium is too low, calcium can accumulate, potentially leading to increased cramping, fatigue, or delayed recovery.

Experts recommend that athletes engaged in strenuous training may need 10 to 20% more magnesium than the general population [2]. Supplementation may be helpful for some, particularly during periods of heavy mileage, but because standard blood tests often fail to reflect actual magnesium status, any supplementation should be based on symptoms, dietary intake, and guidance from a healthcare professional [2].

Calcium

We most often think of our bones when it comes to this mineral; however, calcium is also essential for muscle contraction, nerve signaling, and hormone regulation, all of which contribute to athletic performance.

For runners, the risk of calcium insufficiency is elevated due to several overlapping factors. High-impact training increases skeletal stress and calcium turnover, while low energy availability (whether intentional or unintentional) can impair calcium metabolism and bone remodeling. Female athletes with menstrual dysfunction (e.g., amenorrhea) are particularly vulnerable, as hormonal changes can reduce calcium absorption and bone density over time. Diets that limit or completely restrict dairy, without adequate alternatives, further increase the risk.

Unlike some nutrient deficiencies, low calcium status doesn’t immediately produce obvious symptoms. The body will pull calcium from bones to maintain blood levels, silently weakening skeletal integrity. Over time, this can lead to stress fractures, poor bone healing, and long-term reductions in bone mineral density.

Meeting calcium needs through food is the first priority. Dairy products remain the most concentrated and bioavailable sources, but fortified plant milks, leafy greens (i.e., bok choy and kale), tofu set with calcium sulfate, and canned fish with bones can also help. During periods of high training load, growth, or injury recovery, some athletes may require up to 1,500 mg daily, in divided doses (note: the body can only absorb 500 mg of calcium at a time!). If calcium needs can’t be met through food alone, supplementation may be appropriate, but should be considered alongside vitamin D status, overall energy availability, and under professional supervision.

Vitamin D

Optimal vitamin D levels are crucial for runners to maintain bone density, support muscle function, and regulate immune health as these directly impact training capacity, performance, and injury risk [3]. Unlike many nutrients, vitamin D is unique in that the body primarily synthesizes it through skin exposure to sunlight. This makes runners particularly vulnerable to deficiency, especially those who train indoors, live at northern latitudes, consistently wear sunscreen, or run early in the morning or late in the evening when UVB rays are minimal.

Inadequate vitamin D can quietly undermine performance by reducing calcium absorption, leading to weaker bones and a higher risk of stress fractures. It may also impair muscle recovery and weaken immune defenses, increasing susceptibility to illness during heavy training cycles. Since dietary sources of vitamin D are limited (mainly fatty fish, egg yolks, and fortified foods), runners need to be intentional about both their sun exposure and nutrition.

Importantly, because vitamin D is fat-soluble, it requires dietary fat for proper absorption. Athletes who chronically restrict fat intake (often due to misinformation, attempts at weight control, or a fear of GI distress before workouts) may unknowingly impair vitamin D absorption. While it’s common to limit fat before runs to reduce gastrointestinal upset, this practice should be balanced with ensuring adequate fat intake throughout the rest of the day. Over-restriction, particularly in endurance athletes or those following low-calorie diets, can contribute to deficiencies and long-term health consequences.

Blood testing can help identify a deficiency, especially in athletes with frequent injuries or those training in low-sunlight environments [3]. When necessary, vitamin D supplementation can help restore optimal levels [3] but should be tailored to individual needs under the guidance of a healthcare provider.

B Vitamins

B vitamins are essential for runners to perform and recover effectively given their role in converting food into usable energy, supporting red blood cell production, and maintaining a healthy nervous system. Since endurance training increases energy demands, the need for these nutrients rises accordingly. 

Runners who follow restrictive, plant-based, or low-carbohydrate diets may face an increased risk of nutrient deficiencies. Athletes with celiac disease are also vulnerable since many gluten-free products lack B vitamin fortification. These deficiencies can result in symptoms like fatigue, delayed recovery, and, in severe cases, nerve complications.

Whole grains, legumes, leafy greens, eggs, dairy, and animal proteins provide most B vitamins, while fortified cereals and nutritional yeast are good options for those avoiding animal products. Although most athletes meet their needs through a balanced diet, supplementation might be necessary, particularly for vegans, athletes with dietary restrictions, or those experiencing unexplained fatigue. As always, the choice to supplement should be after consulting with a healthcare provider or a registered dietitian.

 

Key Takeaways

• Meeting overall energy needs is the foundation for maintaining adequate micronutrient status and supporting endurance performance.
• Iron, calcium, vitamin D, magnesium, and B vitamins each contribute uniquely to oxygen transport, bone health, muscle function, and recovery.
• Runners are particularly vulnerable to deficiencies due to factors such as increased nutrient losses through sweat and impact, dietary restrictions, and high training volumes.
• While food-first strategies are best, some runners may require supplementation; this should always be guided by a qualified healthcare or nutrition professional.
• Working with a registered dietitian who specializes in sports nutrition ensures your nutrition plan aligns with your training demands and supports overall health.

 

 

References

1. Solberg A, Reikvam H. Iron Status and Physical Performance in Athletes. Life (Basel, Switzerland). 2023;13(10):2007. doi:https://doi.org/10.3390/life13102007 (source B)
2. Maria Grazia Tarsitano, Quinzi F, Folino K, et al. Effects of Magnesium Supplementation on Muscle Soreness in Different Type of Physical activities: a Systematic Review. Journal of Translational Medicine. 2024;22(1). doi:https://doi.org/10.1186/s12967-024-05434-x (source A)
3. Yoon S, Kwon O, Kim J. Vitamin D in athletes: Focus on Physical Performance and Musculoskeletal Injuries. Physical Activity and Nutrition. 2021;25(2):20-25. doi:https://doi.org/10.20463/pan.2021.0011 (source c)