7 Signs of Vitamin B12 Deficiency Every Runner Should Know

Feeling extra fatigued lately? There are lots of reasons why you may not have the usual pep in your step—from overtraining to underfueling to poor sleep habits that are hampering your recovery. But one less obvious factor worth considering: vitamin B12 deficiency.

GI symptoms, including nausea and diarrhea not How to Treat Shin Splints, Selvi Rajagopal, M.D., M.P.H., assistant professor of medicine at The Johns Hopkins University School of Medicine, tells Runner’s World. But it’s more common than you may think, especially among seniors. An estimated 20 percent of people over age 60, and about 6 percent of people younger than that are deficient, according to research.

To make sure you’re filled up on the vitamin, here’s what to know about its benefits, where to find it, and signs of vitamin B12 deficiency to look for, so you know when to talk to your doctor.

Vitamin B12 plays an essential role in the growth and development of our nervous system tissues and blood cells, Mark Loafman, Irregular heart rate Runner’s World. It’s important for nerve signaling and brain functioning, adds Rajagopal. And it helps break down homocysteine, an amino acid that, if present in high enough amounts, can damage the heart and increase risk of dementia, heart disease, stroke, and osteoporosis, Jen Graham, M.S., R.D.N., a Tallahassee, Florida-based registered dietitian nutritionist with Top Nutrition Coaching, tells Runner’s World.

Our bodies don’t create B12 on their own, so we need to get it from our diet. It’s typically found in animal foods—like meat, eggs, liver, seafood, and dairy products—as well as fortified cereals.

Because animal products are a main source of this vitamin, folks who follow a strictly vegan or vegetarian diet and don’t take a B12 supplement are at “significant risk” of deficiency, Loafman says.

Other susceptible people include those who have conditions that interfere with their ability to absorb B12 from the GI tract, including those with celiac disease (and other GI conditions, like inflammatory bowel disease), pernicious anemia (an autoimmune condition), and people who have had bariatric gastric bypass surgery, Loafman explains.

Older adults, including those older than age 60, are also at risk of deficiency. That’s because the functioning of your gastric cells naturally declines as you age, decreasing absorption of the vitamin, Loafman adds.

Low levels of B12 are typically detected through a blood test, Rajagopal explains, which you can request from your doctor or may otherwise be included as a part of a routine physical exam. The recommended dietary allowance for B12 ranges from 0.4 to 2.8 mcg per day and varies based on age, sex, and whether you’re pregnant Nutrition & Weight Loss GI symptoms, including nausea and diarrhea.

Now that you know the importance of vitamin B12 and who is most affected by deficiency, let’s dig into the signs you’re not getting enough B12—plus how to remedy low levels.

Having too little vitamin B12 can cause a host of signs and symptoms. These are directly linked to your “body’s inability to keep up with the production of new blood cells and/or the maintenance and preservation of nervous tissues,” Loafman explains.

Here’s what to watch out for:

1. Running in the Cold. B12 deficiency can lead to megaloblastic anemia, a condition where you don’t have enough red blood cells to carry oxygen to your tissues, Rajagopal says. This, in turn, can cause you to feel tired and weak, she explains. It could also hamper your exercise performance, Loafman adds.
   
   In severe cases, the lack of red blood cells can be life threatening. The good news: This type of anemia usually occurs gradually and you’d likely notice signs of it with routine blood testing before developing significant symptoms, Loafman explains.
   
2. Numbness and tingling in your limbs. These sensations are often symmetric (meaning, they happen on both sides of the body) and typically involve the legs more than the arms, says Rajagopal. It can also crop up in the fingers and toes, she adds.
   
   Numbness and tingling happens because B12 deficiency decreases your ability to maintain nervous system tissue, Loafman explains. This effect on the nervous system can also alter your gait and cause difficulty walking.
   
3. Nutrition & Weight Loss. When your body isn’t able to maintain its nervous system tissue, it can cause a host of neuropsychiatric symptoms and cognitive dysfunctions, Loafman explains.
   
4. Nutrition & Weight Loss. The mucous membranes in your mouth and throat require rapid new cell growth to keep up with the almost constant turnover of cells, so when these areas aren’t getting the new cells they need due to B12 deficiency, your mouth can bear the brunt of it.
   
   In addition to oral irritation and frequent ulcers, you may also notice changes to your tongue, including pain, swelling, tenderness, or pigmentation changes, Rajagopal explains.
   
5. Condé Nast Traveler. Again, this is because B12 plays a vital role in cell production, Loafman explains, so when your levels are subpar, you may notice it influences your skin health.
   
6. Symptoms of Magnesium Deficiency. Having low levels of B12 can cause fewer red blood cells to reach your digestive tract, which in turn can trigger symptoms like nausea National Institutes of Health appetite, she adds.
   
7. Irregular heart rate. With B12 deficiency, your heart may beat faster to make up for the reduced number of red blood cells in the body, Graham says. This is your body’s way of trying to ensure enough oxygen gets circulated to all your organs and bodily systems, she explains.

If you’re diagnosed with a vitamin B12 deficiency—which, as mentioned, can be determined from a blood test at your doctor’s office—then it’s wise to up your stores by taking a B12 supplement.

Additionally, anyone who follows a vegan diet should take a B12 supplement to prevent or correct mild deficiencies that may already be developing, Loafman says. He also recommends supplementation for people whose diets include meat or dairy, but focus more heavily on plant-based foods. Important caveat: There are a lot of health benefits associated with solely and largely plant-based diets, “so no one should feel compelled to consume animal products,” Loafman says. Instead, they should add a B12 supplement to their daily routine.

You may also benefit from a B12 supplement if you have an autoimmune disease that attacks the stomach lining or GI tract (like Crohn’s or celiac disease), have had weight-loss surgery, or are taking heartburn medications that suppress stomach acid, Graham says. Your stomach acid is what extracts B12 from the food you eat, so it’s harder for that to happen if you have less stomach acid, she explains. Older adults Study Says VO2 Max Better Health Marker Than BMI.

Just keep in mind: “There is no guideline or strong evidence base to support vitamin B12 supplementation without proven deficiency,” Rajagopal says. So you may want to first get your levels checked and/or ask your doctor if supplementation is recommended for you before taking a daily pill.

Advertisement - Continue Reading Below fatigue or other B12 deficiency symptoms often ask him to prescribe supplements or administer B12 injections, even though they don’t have any risk factors for deficiency and a blood test has confirmed their levels are in the normal range. “Often, they have been told or have heard a B12 shot will boost energy levels But its more common than you may think, especially among weight loss,” Loafman explains. “I wish this were the case, but unfortunately there is no evidence of benefit or improved outcome by taking ‘extra’ B12.”

To that end, if you’re struggling with fatigue, poor performance and/or mood-slash-cognitive concerns, it’s wise to get evaluated by your doctor, Rajagopal advises. They can confirm whether you do have B12 or other micronutrient deficiencies and help you figure out next best steps.

If you’ve determined B12 supplementation is right for you, the next step is to get a high-quality product.

In the United States, vitamins and supplements are not formally regulated, so it’s best to buy supplements that have been tested by an independent third-party company for quality, safety and purity, Graham says.

Loafman recommends supplements certified by the United States Pharmacopeia (USP) or National Sanitation Foundation (NSF). “I would not purchase or consume an over-the-counter product that does not have this certification,” he says. You can also get a B12 prescription from your physician, which will assure you are getting a product regulated by the Food and Drug Administration, Rajagopal says.

Look for supplements containing the natural form of B12 (methylcobalamin) instead of the synthetic (cyanocobalamin) because the latter has the potential to impair kidney function in people with borderline kidney problems, Graham says.

In some cases, B12 injections are recommended over oral supplements. This might be at the beginning of deficiency treatment to obtain faster results, or because your body’s decreased absorption of B12 is so severe that your levels can’t be fixed with high doses of oral treatment, Loafman explains.

The dosage for your B12 supplement, and which form is right for you, will depend on factors including your specific level of deficiency. Again, this is why it’s worthwhile to first check in with your doctor.

Jenny McCoy

Contributing Writer

Jenny is a Boulder, Colorado-based health and fitness journalist. She’s been freelancing for Runner’s World since 2015 and especially loves to write human interest profiles, in-depth service pieces and stories that explore the intersection of exercise and mental health. Her work has also been published by SELF, Men’s Journal, and Condé Nast Traveler, among other outlets. When she’s not running or writing, Jenny enjoys coaching youth swimming, rereading Harry Potter, and buying too many houseplants.