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Signs you may be dealing with a nutrient deficiency

How to spot iron, vitamin D, vitamin B12 and magnesium issues

Runners ask a lot of their bodies, which is why nutrition is so key for proper recovery and longterm success in the sport. However, despite their best efforts, people can miss the mark sometimes when it comes to fuelling. If you’ve found yourself feeling a little off, there are a few signs that nutrition is to blame. 

Jennifer Sygo is a registered dietitian and runner who helps Team Canada athletes make good nutrition choices every day. She says there are a few key nutrients that most runners are low on, including iron, vitamin B12, vitamin D and magnesium. Here’s how to tell if you might be low, too. “You can test for all of these in blood work. If you’re showing some signs, getting a test is your best bet.”

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Sygo says this is the nutrition issue that comes up the most – iron deficiency. “We have to be aware that iron deficiency affects females but it can also affect runners in general more than other people. This is because the heel strike [braking motion] harms the red blood cell count. Runners can be more prone to this, so they need to keep an eye on their iron levels.”

Signs of deficiency: fatigue and compromised endurance (not just tired day-to-day, but also when you’re training), paleness, shortness of breath, hair breakage, cold hands and feet and low mood.


B12 comes from animal foods, particularly red meat, so this is of note for runners who are also vegetarian or vegan. “If you’re not getting enough [which can happen with plant-based diets], the B12 symptoms can look similar to those that low iron gives you. You’ll also feel fatigue, compromised endurance and general weakness.”

Signs of deficiency: If B12 deficiency gets severe enough, you may start to notice nerve changes, like pins and needles. Runners might also notice mood changes as well. 

Vitamin D

Vitamin D comes from the sun, so all Canadians are prone to deficiencies. This vitamin is particularly important for runners as  it’s key for building healthy bones.

Signs of deficiency: Bone pain, especially soreness in the back or shins. “If you press on your sternum and it feels tender, that’s an indicator that you’re low and you should get your blood checked,” Sygo says. Runners might also feel things like muscle aches and weakness.


Magnesium mostly comes from nutrient-dense foods like nuts, seeds and whole grains. “Runners have to eat a quality diet. Becoming low on magnesium happens when people eat a lot of highly processed or grab-and-go foods. Actually, about 25 per cent of the U.S. population is low on magnesium.”

Signs of deficiency: constipation, aching muscles, cramps, irregular sleep and insomnia. 


While carbohydrates are a macronutrient and not a vitamin or mineral, it’s still something that runners can become low on if they’re not careful. “Athletes who become too cautious with their diet, especially with their carb intake, can crave sugar later in the day. This is because their body isn’t getting enough, which creates these cravings.”

Signs of deficiency: sugar cravings later in the day. “There’s a lot of messaging around low carb diets, but as a runner you do need carbs. If you’re having a salad, for example, make sure you have rice or sweet potato with it too.”

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