I Blamed My Training Fatigue on a Running Slump. A Nutrient Deficiency Was the Real Culprit.

Jump to:Common Nutrient Deficiencies in RunnersIs It a Nutrient Deficiency or Burnout?Treat Your Deficiency—and Bounce Back in TrainingI remember my legs and arms moving in slow motion, as if restricted by the resistance of water. Only I wasn’t swimming—or anywhere near a pool.Instead, I was in Lane 2 of my college track, running lap after lap around the blue oval with my teammates as we took on an ordinary 300-meter repeat workout. Yet on that day during my sophomore spring track season, I was simply willing myself to the finish line with each rep.Normally, I loved workouts where I could lock into a pace, push the intensity, and challenge my body. But that 300-meter repetition session felt different. From the start of the workout, I lacked the energy my muscles usually had to power through. Rather than hitting controlled, sub-60-second splits for each rep, I strained to hit the finish line in 65 seconds and watched my teammates pull ahead of me. I felt like my body was burning out—both physically and mentally. And the icing on the cake: I’d noticed similar fatigue during some easy runs and races in the weeks prior. But were those symptoms because of a running slump, overtraining, or something different entirely?Stuck in a training rut? Explore the Runner’s World Guide to Getting Out of a Training Slump for expert guidance on recognizing burnout, finding your motivation, and making a comeback to your running journey.I sat at the campus health center as a doctor walked through blood panel results with me a week later, a step my coach urged me to take after that brutal track workout. Turns out, I had both vitamin D and iron deficiencies. As the doctor explained, the fatigue and muscle weakness I experienced were likely a result of my low vitamin D and ferritin (the form of iron stored in the body) levels.I couldn’t wrap my head around how I’d developed the deficiencies in the first place, but the doctor had some ideas. I ate a well-balanced diet and spent plenty of time outside soaking up the vitamin D-rich sunshine, but my training load and predisposition to iron deficiency as a female runner simply meant I needed more of the two nutrients in my regular intake, the physician theorized. Luckily, I had answers to my fatigue and performance problems, but it would take some time, strategy, and doctor’s orders to feel more like myself again as a runner.Nutrient deficiencies can affect any runner, and they often share symptoms common to running slumps and overtraining. Knowing how to differentiate between regular fatigue and soreness and symptoms caused by nutritional deficits can keep you on a healthy running trajectory. “I think for anyone who has trained for a marathon or an endurance event, you're not always the most energized,” says Amy Goblirsch, RDN. “It can be hard to see that small line that can be just general fatigue from asking a lot from your body.”You can stay on track with your training and keep burnout at bay by understanding some of the most prevalent deficiencies found in runners.Common Nutrient Deficiencies in RunnersWhile it’s important to keep regular tabs on all of your nutrient levels by undergoing routine bloodwork—ideally before every training cycle—some specific vitamin deficiencies are more common in runners than others, and can lead to negative impacts on your training such as fatigue, muscle weakness, and slowed recovery.IronOne of the most crucial nutrients for runners: iron. The nutrient makes hemoglobin, responsible for carrying oxygen in your blood to your muscles. With an inadequate amount of iron, you may notice your pace, endurance, and recovery suffer, as well as experience increased fatigue and difficulty finishing speedwork and quality sessions. You also may develop anemia, a condition where your body can’t produce a normal amount of healthy blood cells, which significantly inhibits oxygen transport throughout your body.Runners need to have higher ferritin levels than the typical individual because they lose more iron through exercise, and use up more iron to make red blood cells and transport oxygen. Female runners also excrete more iron through menstruation each month, putting them at greater risk of developing a deficiency. While the normal ferritin range for an average person is anywhere from 10 to 15 ng/mL, a runner should have levels between 30 and 50 ng/mL to perform at their best.Often, runners will notice the performance impacts first when they have an iron deficiency. “[Runners will] say, ‘I can’t run quite as fast or quite as far,’ or ‘I can’t do as many reps,’” Ariela Marshall, MD, an American Society of Hematology expert, previously told Runner’s World. “Or, ‘I’m doing the same workout, but I feel tired during it’ or ‘I feel much more tired than I usually would after I finish.’”You may also notice the other common signs of an iron deficiency during your training, including:DizzinessHeadachesShortness of breathTrouble concentratingMood changesEasy bruisingHair lossHeart palpitationsPica, or the eating of non-nutritive substances (e.g., ice)Vitamin DKnown as the sunshine vitamin, vitamin D is especially important for runners. It supports your muscle function, immune regulation, calcium absorption, and even bone remodeling and health. (No wonder I felt like I was moving in slow motion during my track workout.)But don’t let vitamin D’s sunny moniker fool you. “Runners may think that because they spend a lot of time outside, they’re getting [the vitamin D] they need from the sun,” board-certified sports dietitian Kelly Jones previously told Runner’s World. “However, we’ve seen in research studies on those who exercise outside, and I’ve seen firsthand in my outdoor sport athletes who have regular blood work done, that many will still have vitamin D levels that are inadequate or even clinically deficient.”For runners, targeting a vitamin D level of at least 75 to 80 nmol/L is recommended by experts for supporting your health, immune system, muscle function, and running routine.Symptoms of a vitamin D deficiency can include:FatigueMuscle pain, weakness, or crampsTingling in your hands or feetMood changesFrequent illnessSusceptibility to bone stress injuryVitamin B12For strong, sustained running, you need oxygen. That’s where vitamin B12 comes into play, supporting your red blood cell production crucial to oxygen transport throughout your body, as well as DNA synthesis, neurological function, and nervous system tissue development.You may notice the following symptoms when experiencing a vitamin B12 deficiency:FatigueReduced exercise capacityNumbness and tingling in your limbsMood changesNausea or diarrheaIrregular heart rateSkin changes, such as rashes or pigmentationOral irritation, including frequent ulcersResearch on vitamin B12 levels in athletes suggests that a range of 400 to 700 pg/mL is best for supporting optimal exercise and performance. Though most people aren’t at risk of a vitamin B12 deficiency—typically classified as 200 pg/mL or less—it’s more common among certain demographics, particularly seniors. According to some research, an estimated 20 percent of people over the age of 60 have a vitamin B12 deficiency. People who follow a vegan or vegetarian diet may also be at a higher risk of developing a deficiency since animal products are the main source of vitamin B12, as well as those with health conditions that inhibit B12 absorption from the GI tract.MagnesiumFor proper muscle function, energy production, and healthy nerves and bones, you need magnesium in your regular diet. It’s a micronutrient essential for synthesizing protein in the body, powering your muscle and nerve function, and even regulating your blood sugar and blood pressure. According to the National Institutes of Health, the common, healthy range for blood magnesium level is between 0.75 and 0.95 mmol/L.Common signs of a magnesium deficiency include:FatigueReduced exercise toleranceMuscle weakness or crampingImpaired neuromuscular functionNausea or loss of appetiteIs It a Nutrient Deficiency or Burnout?Many of the signs of vitamin and nutrient deficiencies are common enough in our daily lives that they can be easy to dismiss as relatively normal. If you’re in a marathon block and feel excessively fatigued and sore, you may just chalk it up to your higher training volume and intensity. A handful of tough workouts, and you may wonder if those stressful days at work are catching up to you. You may blame constant headaches and irritability on simply spending a lot of time running—perhaps too much.For better understanding of whether a deficiency may be sabotaging your training, look first at your daily food intake. If you’re not increasing your caloric needs to match your mileage, or struggle to eat after hard workouts or long runs, you could be digging yourself into a nutritional hole. Even factors such as external stress could affect your fueling routine and potentially lead to nutritional deficiencies. “Especially with runners that I work with, again, they’re not professional athletes,” Goblirsch says. “They have full-time jobs, and there’s a lot of work stress, or maybe they’re having all of these back-to-back meetings and they’re struggling to meet their intake. Then, that could end up turning into a deficiency.”You know your body best. If you’re noticing red flags aligned with a vitamin deficiency, and see your training heading down a dark path, it’s important to seek medical attention and get to the root of the problem.I was fortunate to have a coach who encouraged me to get a blood screening at my school’s health center, but if you don’t have a run coach or other expert at your disposal, it’s important to be honest with yourself about your symptoms. A general rule of thumb: If your symptoms begin to consistently impact your life outside of running, it’s time to visit an expert.Treat Your Deficiency—and Bounce Back in TrainingThe most accurate way to determine whether your fatigue, muscle soreness, or reduced exercise capacity is due to a deficiency is to get bloodwork done by your physician or medical provider. Update your medical provider on your running history and training demands to ensure they fully understand your nutritional needs and know what vitamins and nutrients to screen for in your blood panel. If you’re diagnosed with a deficiency following a blood screening, your doctor or dietitian will likely provide you with a dietary and supplementation plan to boost your levels for supporting healthy training and lifestyle.Adding food sources rich in iron, vitamin D, magnesium, vitamin B12, or whatever vitamin you’re lacking into your diet can aid your recovery, but taking a supplement suggested by your doctor is often necessary for significant results. How quickly you’ll see differences in your bloodwork and symptoms depends on the type of vitamin deficiency and severity of it, but it could take anywhere from a few weeks to many months. You could also notice your energy levels increase and symptoms subsiding even before your nutrient levels show improvement on a blood panel.In my case, I needed a few months to regain that spring in my step. I took both an iron and a vitamin supplement daily (a routine I still follow five years later), plus added foods rich in each nutrient into my meals more frequently, including red meat, spinach, fortified cereal, and milk. But come time for my summer training block, all of those treatment steps helped me reach a point where I could tackle miles feeling stronger than ever.Knowing warning signs to look for, and understanding when training fatigue could mean something more, can make the biggest difference in quickly catching and treating deficiencies—and getting you back on track with your healthy running regimen.Ashley is Editor of Content Hype at Hearst’s Enthusiast & Wellness Group. She is a former collegiate runner at UNC Asheville where she studied mass communication. Ashley loves all things running; she has raced two marathons, plus has covered some of the sport’s top events in her career, including the Paris Olympics, U.S. Olympic Trials and multiple World Marathon Majors.