Pro Athletes Focus on These Biomarkers. Here's Why You Should, Too.

By Michelle Darian, MS, MPH, RD, September 2, 2021

man running professional athleteInsideTracker users have been able to uncover seemingly small details in their bloodwork that have proven implications on their athletic performance. We (virtually) sat down with a few athletes who’ve shared their Inside Story, and you may find that you have a few things in common with these professionals. 

endurance trainingIron and ferritin are critical, but optimal levels can be elusive for athletes and non-athletes alike

Iron is an essential mineral that is a part of the protein hemoglobin, which is found in all the body’s red blood cells. Hemoglobin works to supply the muscles and other organs with oxygen, as well as to help the body convert carbohydrates and fat into energy. Maintaining optimal levels of iron is essential for athletes and non-athletes alike, as iron plays many important roles in the body. Ferritin is also important to watch. As a type of protein that binds iron, ferritin is most associated with iron storage. In fact, most of the iron stored in the body is bound to ferritin, which makes it a good marker of your body’s iron capacity. 

Despite its critical importance for various processes throughout the body, low iron and iron deficiency are relatively common. This is at least in part due to iron absorption, which can be tricky and dependent on both the source and the timing of consumption. Good sources of iron include red meat, shellfish, beans, dark chocolate, fortified cereals, and dark leafy greens, and are best absorbed when paired with a vitamin C rich food.

Sometimes, blood levels indicate the need for iron supplementation. If you take an iron supplement, ensure you take it at the optimal time; iron supplements and iron-rich meals are best absorbed when they are not taken before or after exercise, due to the increased inflammation following a workout. The ideal time for taking an iron supplement is one hour before a meal, or two hours after, to ensure an empty stomach. The InsideTracker Iron Group provides a comprehensive way to understand your current iron status, and gives you personalized recommendations to ensure optimal levels. 


Your body loses iron during heavy training periods through sweating, running, and the (minor) gastrointestinal bleeding that can sometimes follow intense workouts. It's therefore very important to monitor your iron intake to ensure adequate blood levels. Athletes with low levels of iron can experience reduced oxygen capacity in the lungs (VO2max) and anaerobic capacity.[1]

Pre-menopausal women are at an increased risk for depleted iron levels due to the loss of hemoglobin in blood during menstruation. In particular, female athletes are three times more likely to be anemic than non-athletic women. Finally, vegetarians are also at risk of iron-deficiency because the iron in plant-based foods (non-heme iron) is harder for the body to absorb than the iron in animal products (heme iron).[2]

Spartan Ultra World Champion and endurance coach Rea Kolbl has used InsideTracker to level up her performance over the last five years. “InsideTracker played an important role in first discovering my anemia with extremely low ferritin levels in 2016,” she says. Watch Rea's video below to learn how this discovery was critical to her competitive performance.



Vitamin B12 is essential for both endurance athletes and those simply looking to live longer

Vitamin B12 is essential for the production and maintenance of red blood cells, nerves, and DNA. Inadequate B12 can lead to anemia—a deficiency of red blood cells that can reduce your body's oxygen capacity and cause you to feel tired and weak. Vitamin B12 deficiency can also cause skin numbness, poor coordination, poor mental health, and decreased cognitive function. But more isn’t always better; excess B12 is associated with dizziness, anxiety, and even skin conditions

Vitamin B12 comes primarily from animal products and their byproducts (meats, eggs, milk, cheese, etc.). Plant-based sources of B12 can be found in nutritional yeast, fortified foods like milk and cereals, and in supplements. For individuals with low levels of B12, InsideTracker recommends supplementing, but blood tests are necessary to determine current B12 status.

Vitamin B12 has been linked to factors related to aging. B12 impacts the myelination of your nervous system, which protects your brain cells and nerves from deteriorating over time. Evidence suggests that there may be a relationship between B12 and cognitive function in older age, with low B12 levels being suggestive of increased risk of dementia.

This relationship between B12 and age is made more complex by the change in B12 absorption across the lifespan. The digestion and absorption of B12 is dependent on both stomach acid and a protein called intrinsic factor (IF). Stomach acid unbinds B12 from food, allowing it to combine with IF, which then facilitates its absorption into our bloodstream.[3] Interestingly, older age has been associated with a decreased production of both gastric acid and IF, making B12 harder for the body to absorb. For this reason, it's imperative that older populations monitor their B12 levels to mitigate this higher risk for vitamin B12 deficiency. 

Mike Wardian

Athletic individuals also need to pay particular attention to their vitamin B12 levels. Vitamin B12 plays a role in the synthesis of new cells, specifically red blood cells. One study found that vitamin B12 was associated with hemoglobin synthesis, which we've established as critical for athletic performance and optimal endurance capacity.[4]

Renowned ultra-marathoner Mike Wardian shared what he’s learned about himself through InsideTracker:  “As a plant based athlete, I am always determined to ensure that I am getting enough protein, iron, and B12 and with InsideTracker, I’m able to confirm those details.” 


Vitamin D isn't just a fan favorite among pro strength athletes

Vitamin D plays a role in nearly every pathway in the body, including aiding the absorption of calcium in the bones, controlling inflammation, supporting immune responses, improving cardiovascular health, glucose metabolism, cell proliferation, and much more. However, it's relatively scarce from food sources, often making it a challenge to meet dietary needs. And while the sun stimulates the production of vitamin D in the body, it may not be enough to keep you covered. 

Foods like fatty fish (e.g. halibut, carp, and eel), maitake (Hen of the woods) mushrooms, and pork contain some vitamin D. Food isn't the only source, though—20 minutes of direct sun exposure each day can help to maintain your current vitamin D levels. Depending on your vitamin D blood levels, it may be recommended to add a vitamin D supplement to your regimen, but the best way to know what your body needs is to get your vitamin D level measured via blood test. 


Vitamin D has caught the attention of longevity experts because of its pervasiveness in various systems in the body. It's also explicitly connected to processes associated with aging. First, it is well-established that adequate levels of vitamin D play a critical role in the prevention of osteoporosis and reduced severity of bone fractures in older adults.[5] Low levels of vitamin D have also been associated with factors of cognition ranging from depression and mild memory loss to dementia.[6]

Maintaining optimal levels of vitamin D can also disrupt  immunosenescence, or the gradual decline of the immune system due to aging, as vitamin D modulates the innate and adaptive immune responses known for fighting off pathogens in the body.[7] It's important to note, however, that vitamin D needs increase as we age due to a natural decrease in absorption over time, and therefore staving off immunosenescence can become more difficult over time.

Optimal vitamin D levels can also help build strength and improve athletic performance. Studies show that vitamin D acts directly on muscle to increase protein synthesis, enabling increased muscle mass and decreased muscle fiber degradation. Optimal vitamin D levels have also been shown to increase the size and number of muscle fibers associated with building strength.[8]

Holley is a registered dietitian and runner who regularly tests with InsideTracker. Holley felt like she was doing all of the right things to maintain (and even improve) her vitamin D levels, but her most recent InsideTracker test results revealed that her vitamin D was trending downwards. Armed with new strategies, Holley is ready to get her vitamin D levels back into her optimal zone. 




Michelle Darian photo
Michelle Darian, MS, MPH, RD
Michelle is a Nutrition Specialist at InsideTracker. As a Registered Dietitian, you’ll find Michelle analyzing the research behind recent nutrition trends, bringing actionable food and supplement recommendations to the platform. When she's not myth-busting, Michelle can be found exploring new restaurants and getting creative in her kitchen.











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