Feeling Fatigued After Working Out? You Could Be Deficient in These Key Vitamins and Minerals


A registered dietitian explains how three different nutrient deficiencies could be the cause of major fatigue post-workout.

Last updated: 27 July 2022
6 min read
3 Vitamin and Mineral Deficiencies That Could Derail Your Workout

Nothing feels better than cruising through a workout before cooling down. But what's going on if you're struggling to complete workouts that you might typically consider easy? While it's totally normal to have a few workouts feel less than optimal, if you repeatedly finish a sweat sesh feeling completely wiped, it might be a sign that something is off in your body.

Sure, an intense workout can leave you tired, but if you feel like you are constantly hitting a wall in your workout, it could be due to a vitamin or mineral deficiency.

What nutrients could contribute to fatigue if you don't consume enough?

Trying to work out without following a proper diet is like trying to take a road trip on a quarter of a tank of petrol. Things might start off OK, but eventually you're going to run out of fuel.

To maintain consistency, strength and overall health, it's imperative you consume a variety of nutrients to support your body through the physical demands of working out. But, there are two vitamins and one mineral that stand out when it comes to supporting athletic performance: vitamin B12, vitamin D and iron.

  1. 1.Vitamin B12

    Vitamin B12 naturally occurs in many foods and is even added to some foods during processing. The best sources of vitamin B12 are found in animal products such as yoghurt and cheese, seafood, beef, eggs and some types of poultry. Some plant-based foods have vitamin B12 added to them, such as nutritional yeast and breakfast cereals; however, vegetarians and vegans tend to be at higher risk of vitamin B12 deficiency. According to the Institute of Medicine, the recommended dietary allowance of vitamin B12 for adults aged 19 and older (who are not pregnant or breastfeeding) is 2.4 micrograms per day.

    Vitamin B12 is critical for many reactions in the body, but when it comes to energy levels, it plays a big role in supporting a healthy nervous system and red blood cell formation. Healthy red blood cells are necessary to transport oxygen throughout the body. Without properly developed red blood cells, muscles and tissues will not get the oxygen they need to support you through your workout. In addition, if your motivation to get moving has been dipping, a vitamin B12 deficiency could be partially to blame, as low levels of vitamin B12 have been associated with a higher risk of depression.

  2. 2.Vitamin D

    Vitamin D is a powerful player in overall health and well-being—but it's only found naturally in a few foods. Many foods such as milk, some orange juice and some breakfast cereals have been fortified with vitamin D to help increase its consumption. The amount of vitamin D that's present in animal foods such as fish, eggs and dairy products depends on what the animals themselves have been eating.

    Another way you can get vitamin D? Sunlight—your skin absorbs light from the sun and creates vitamin D in the body. According to the Institute of Medicine, the recommended dietary allowance of vitamin D for adults aged 19–70 is 600 IU per day (again, for those who aren't pregnant or breastfeeding). For context, half of a fillet of farm-raised Atlantic salmon (178 grams) contains 936 IU, making it one of the richest food sources of vitamin D. And you don't have to worry about eating more than the recommended dietary allowance on some days—data has shown that most Americans don't get enough of the vitamin.

    Necessary for proper immune function and healthy bones and muscles, adequate levels of vitamin D are critical for getting a solid workout done without feeling depleted. Not to mention, the vitamin also helps boost your recovery from a workout, as well.

  3. 3.Iron

    Iron is an essential mineral that plays a key role in moving oxygen throughout the body, promoting energy production and aiding in DNA synthesis. Animal products and plant-based foods can both provide iron, however, the body prefers iron from animal sources as it's better absorbed.

    The Institute of Medicine's Dietary Reference Intakes set the iron requirements for most adult males to roughly eight milligrams of iron daily, however, for people who menstruate and are aged 19–50 the requirements are 18 milligrams per day. After the age of 50, those requirements drop back down to eight milligrams of iron per day for women. Because iron is critical for circulating oxygen through the body to organs, tissues and muscles, if levels of the mineral are not sufficient, you could find yourself feeling fatigued and weak before, during and after a workout.

What are the symptoms of a nutrient deficiency?

Unfortunately, when it comes to a vitamin B12, D or iron deficiency, the symptoms can all mimic one another. Common symptoms of all three deficiencies include fatigue, irritability and body weakness. According to the American Family Physician journal, symptoms unique to vitamin B12 deficiency are a red, swollen tongue and tingling in the hands or feet as well as unexplained weight loss. A unique indication of vitamin D deficiency is frequent injury due to the effect low vitamin D has on bones and muscles. If fatigue is common after working out regardless of the intensity, consider seeing your doctor and requesting a blood test. After all, a blood test is the only way to diagnose a nutrient deficiency.

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Can you prevent vitamin B12 deficiency ... and other nutrient deficiencies?

In general, vegetarians and vegans tend to be at a higher risk of deficiency in all three nutrients since they are primarily found in animal proteins. A 2016 position paper from the Academy of Nutrition and Dietetics noted that though properly planned vegan and vegetarian diets are healthy, taking supplements such as iron, vitamin B12 and vitamin D may be a good idea—especially for vegans.

When it comes to vitamin B12 and iron, omnivores are in luck. As long as a diet is varied in its protein sources and includes nutrient-dense plants such as leafy greens, nuts and seeds, deficiencies of iron and vitamin B12 can largely be avoided, assuming no other underlying conditions are at play. Vitamin D is another story due to the fact that it's found in a limited amount of food, and blood levels also depend on access to sunlight. In winter months—or for those living in areas with limited days of sunlight—taking a vitamin D supplement may be necessary.

Bouncing back from a nutrient deficiency takes time and it is best to work with a registered dietitian who can help tailor the ideal diet and supplement protocol for you. The good news? Supplements will often only be necessary for a short period of time or until levels get back up to baseline.

Words by Sydney Greene, MS, RDN

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Originally published: 17 June 2022