Nutrition Diet: What are runners usually deficient in?

October 3, 2025 •

5 min read

Up to 35% of female athletes are iron-deficient, a rate significantly higher than the general population. This reveals a critical need to understand what are runners usually deficient in to maintain performance and health.

Quick Summary

Runners are prone to deficiencies in key nutrients like iron, vitamin D, calcium, magnesium, and electrolytes due to high demands and sweat loss. Inadequate fueling and micronutrient gaps can compromise performance, recovery, and overall health.

Key Points

Iron is Critical for Oxygen Transport: Runners frequently experience iron deficiency due to intense training, sweat loss, and foot-strike hemolysis, which can severely impact performance.
Bone Health Requires Calcium and Vitamin D: Adequate levels of these two nutrients are vital for maintaining bone density and preventing stress fractures, especially for female athletes and those with limited sun exposure.
Electrolytes Regulate Fluid and Muscle Function: Sodium, potassium, and magnesium lost through sweat can lead to imbalances causing muscle cramps, fatigue, and impaired performance during long or intense runs.
B Vitamins are Essential for Energy Metabolism: As the body's energy requirements increase, so does the need for B vitamins to efficiently convert food into fuel. Vegetarians and vegans may be at risk for B12 deficiency.
Magnesium Supports Muscle Recovery: This mineral is crucial for muscle contraction, relaxation, and energy production. Deficiency is common and can contribute to muscle cramps and poor recovery.
A Balanced Whole-Food Diet is the Best Defense: Relying on a varied diet rich in whole foods, alongside proper caloric intake, is the most effective way to prevent most nutrient deficiencies in runners.
Consult a Professional for Supplements: Before starting any supplementation regimen, runners should consult a healthcare provider or registered dietitian to confirm deficiencies through bloodwork and ensure proper dosage.

The demanding nature of running, particularly for endurance athletes, places a heavy toll on the body. This intense and sustained physical activity increases nutritional requirements and can lead to deficiencies if not properly addressed through a well-balanced diet. Beyond simply needing more calories, runners often face depletion of specific vitamins and minerals crucial for energy production, oxygen transport, muscle function, and bone health. Failing to address these issues can result in fatigue, reduced performance, and an increased risk of injury.

Iron: The Oxygen Carrier

Iron is one of the most common deficiencies observed in runners. This vital mineral is a central component of hemoglobin, the protein in red blood cells responsible for transporting oxygen to the muscles. For runners, consistent oxygen delivery is paramount for aerobic performance. When iron levels are low, oxygen transport is compromised, leading to fatigue, reduced endurance, and shortness of breath. Several factors contribute to iron deficiency in runners:

Foot-strike hemolysis: The repetitive impact of running on hard surfaces can damage red blood cells in the feet, increasing iron loss.
Sweat loss: Iron is lost in sweat, and heavy sweaters, especially in hot conditions, can experience significant cumulative loss.
Menstruation: Female athletes are at a particularly high risk of deficiency due to iron loss through menstruation.
Inflammation: Intense training can cause temporary inflammation, which can disrupt iron absorption for several hours post-exercise.

To prevent or correct low iron, a diet rich in iron-rich foods is essential. The body absorbs heme iron, found in animal products, more readily than non-heme iron from plant sources.

Bone Health Nutrients: Calcium and Vitamin D

Strong bones are fundamental for runners to withstand the repetitive impact of training and prevent stress fractures. Calcium and Vitamin D work synergistically to support bone health; Vitamin D helps the body effectively absorb the calcium it consumes. Without adequate levels, a runner's bone mineral density can decline, increasing their risk of injury.

Vitamin D: Produced by the skin through sun exposure, Vitamin D levels are often insufficient in runners, particularly during winter months or for those who train indoors frequently. It also plays a role in muscle function and immune health.
Calcium: Lost through sweat, calcium intake needs may be higher for endurance athletes. Many individuals, particularly those following dairy-free diets, may not meet their daily calcium requirements.

Electrolyte Imbalance: The Hydration Concern

During exercise, the body loses electrolytes—minerals like sodium, potassium, and magnesium—through sweat. These minerals are crucial for maintaining fluid balance, proper muscle contraction, and nerve function. An imbalance, especially from excessive sweat loss during long or intense runs, can lead to several performance-inhibiting issues:

Sodium: The primary electrolyte lost in sweat. Insufficient sodium intake can lead to hyponatremia, a dangerous condition caused by over-hydration with plain water.
Potassium: Also lost in sweat, it is important for muscle function and can be replaced through diet.
Magnesium: Involved in over 300 biochemical processes, magnesium supports energy production and muscle relaxation. Deficiency can contribute to muscle cramps and fatigue.

For runs over an hour or in hot conditions, replenishing electrolytes is vital. Many sports drinks, gels, and tablets are designed for this purpose, providing a balance of sodium, potassium, and carbohydrates.

B Vitamins: The Energy Metabolizers

The B-complex vitamins (including B1, B2, B6, B12, and folate) are essential for converting carbohydrates, fats, and protein into usable energy. As runners require significantly more energy, their need for B vitamins increases. Deficiencies, particularly B12, can cause fatigue and compromise red blood cell production. Those following plant-based diets should be especially mindful of B12, as it is primarily found in animal products.

How to Prevent Common Runner Deficiencies

Preventing these common deficiencies is primarily about a thoughtful, proactive approach to nutrition. While supplements can help fill gaps, a varied, whole-food diet is the best foundation.

Prioritize a Balanced Diet: Ensure your daily intake includes complex carbohydrates, lean protein, and healthy fats from a wide variety of whole foods. Don't restrict calories excessively, as this is a common reason for under-fueling and nutrient gaps.
Time Your Nutrition: Proper timing of meals and snacks can optimize nutrient absorption. For example, consuming Vitamin C with iron-rich foods can enhance iron absorption.
Consider High-Risk Factors: If you fall into a high-risk group (female, vegetarian/vegan, high-volume training), be extra vigilant about key nutrients like iron and B12. Regular blood tests can help monitor your levels.
Consult a Professional: A registered dietitian can provide personalized guidance based on your specific needs, training volume, and dietary preferences.
Strategic Supplementation: Only supplement when necessary and after consulting a healthcare professional. For example, some runners benefit from a Vitamin D supplement during darker months.


Nutrient	Function	Deficiency Symptoms	Food Sources
Iron	Oxygen transport, energy production	Fatigue, weakness, reduced performance	Red meat, poultry, fish, lentils, spinach
Vitamin D	Calcium absorption, bone health, immune function	Low bone density, stress fractures, poor sleep	Fatty fish (salmon), eggs, fortified dairy, sunlight
Calcium	Bone strength, muscle contraction	Increased fracture risk, muscle cramps	Dairy products, fortified milk alternatives, leafy greens
Magnesium	Muscle relaxation, energy production, nerve function	Muscle cramps, fatigue, weakness	Leafy greens, nuts, seeds, whole grains
Electrolytes	Fluid balance, nerve & muscle function	Muscle cramps, fatigue, confusion	Sports drinks, electrolyte tablets, bananas, potatoes, salty foods
B Vitamins	Energy metabolism, red blood cell formation	Persistent fatigue, poor recovery	Whole grains, meat, eggs, dairy

Conclusion

Running is a physically demanding sport that can put athletes at risk of several key nutrient deficiencies, most notably in iron, vitamin D, calcium, magnesium, and B vitamins. These depletions can manifest as increased fatigue, poor performance, and a higher susceptibility to injury. Female, vegetarian, and adolescent athletes are particularly vulnerable. However, by adopting a holistic nutritional strategy that focuses on a diverse, whole-food diet, strategic nutrient timing, and informed supplementation when necessary, runners can mitigate these risks. Partnering with a sports dietitian or healthcare provider can further ensure that your body is adequately fueled and supported to meet the challenges of training and achieve your goals safely and effectively. Consistent, well-planned nutrition is a critical component of any runner's success.(https://www.hopkinsmedicine.org/health/wellness-and-prevention/runners-diet)

Frequently Asked Questions

Runner's anemia is a form of iron deficiency often seen in athletes, especially endurance runners. It results from increased iron demands, iron loss through sweat and foot-strike hemolysis (the destruction of red blood cells from repetitive foot impact).

Female runners, particularly those who menstruate, are at higher risk of deficiencies like iron due to increased blood loss. Additionally, female athletes sometimes have lower overall energy intake, increasing the likelihood of inadequate nutrient consumption.

Plant-based runners should pay close attention to iron and B12 intake. They can boost iron absorption by combining non-heme iron sources (like lentils and spinach) with Vitamin C. B12, found primarily in animal products, often requires supplementation or consumption of fortified foods.

While often confused, muscle cramps during long, sweaty runs are often linked to an electrolyte imbalance, particularly low sodium and potassium, rather than just dehydration. Electrolytes are crucial for proper muscle contraction and function.

A balanced whole-food diet should be the primary source of nutrients. Supplements should not be taken without first consulting a healthcare professional and potentially getting bloodwork done to confirm a deficiency. Over-supplementation, especially of fat-soluble vitamins like D, can be harmful.

Magnesium can be found in a variety of foods, including leafy greens like spinach, pumpkin seeds, chia seeds, almonds, cashews, and whole grains. Adequate magnesium intake is important for muscle function and preventing cramps.

A deficiency in Vitamin D can impair calcium absorption, leading to weakened bones and an increased risk of stress fractures. It also affects muscle function and immune health, which can lead to poorer performance and increased illness.