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Blood Testing for Athletes: Improving Performance

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Blood Testing for Athletes: Improving Performance

One hallmark of an athlete is the desire to improve performance and gain an edge over the competition, whether through physical power, endurance, mindset work, or other means. Using a functional medicine approach to blood testing, athletes can also better understand biomarkers related to health and performance, helping them optimize their training and recovery plans to be on top of their game. 

Blood testing can provide insights into health concerns that affect performance, like iron levels and nutrient status. Examining markers like cortisol and other hormones can also help gauge recovery efficiency. This article will review blood testing for athletes and how to use blood test results to boost performance.


Why Should Athletes Focus on Blood Work?

Using blood work as part of an athlete's training regimen can be a valuable component to support optimal performance, recovery, and overall well-being. While some biomarkers can directly impact athletic performance, others can be used to better understand an athlete's training schedule and recovery needs and can aid in injury and illness prevention. By evaluating internal stress levels, muscle health, and possible deficiencies in the body, athletes and their coaches can better manage their training, recovery, and nutrition while optimizing athletic performance.  

Athletes can personalize their blood work by considering any possible gaps in their diet (for example, a low-carb diet or a plant-based diet), their health history, and their sports training goals.

The timing of lab testing is an important consideration as well. Some considerations for athletes when testing include the time of day (which can impact hormones such as cortisol), hydration status (dehydration can affect lab results), training load leading up to the blood draw (specific markers are elevated in post-training windows), and for female athletes, day of the menstrual cycle.

What Are The Top Blood Tests for Athletes?

There are several important blood tests for athletes to consider:

Vitamin D

Vitamin D helps keep inflammation at bay while supporting immune health and recovery. Additionally, it has been linked to increases in muscle strength, size, and power. Low levels of vitamin D have been associated with low testosterone levels, a higher risk of injury and stress fracture in athletes, and suboptimal muscle function.  


Cortisol is a hormone produced in response to any type of stressor (physical or mental). It influences circadian rhythm, sleep, blood sugar levels, blood pressure, and energy levels. Chronically elevated cortisol can occur with high levels of training stress (particularly without adequate recovery) and increases an athlete's risk of fatigue, trouble with weight control and maintaining muscle mass, poor sleep, and injury.

Micronutrient Panel

Vitamins and minerals are essential for athletic performance and recovery, as these micronutrients are essential for basic metabolic functions and hormone production and help muscles recover. In particular, zinc, magnesium, iron, and B vitamins are important for athletes to track. Understanding levels of these micronutrients can help fine-tune training and recovery needs and guide any supplementation during high training periods.  

Thyroid Panel: TSH, Free T4, and Free T3

Thyroid testing is essential for athletes to optimize their performance, as low thyroid function has been linked to reduced exercise capacity and endurance performance. The thyroid is also sensitive to prolonged stress and overtraining, and suboptimal thyroid hormone ranges can indicate a need for better recovery methods. A full panel that includes free T4 and free T3, in addition to TSH, is recommended. Using TSH alone as a screening method for early hypothyroidism can't reliably identify more subtle changes in the hypothalamic-pituitary-thyroid (HPT) axis that are common with ongoing stress, like high training periods.  

Creatine Kinase

Creatine kinase is an enzyme that can be analyzed to see how an athlete is reacting to muscle damage during a high training load. It peaks roughly 2-4 days after an intense workout session, so the testing window is vital for this blood marker. Chronically elevated creatine kinase levels have been linked to muscle pain, soreness, weakness, and a higher risk of injury.  

It should be noted that ongoing creatine supplementation can falsely elevate creatine kinase, so understanding what supplements an athlete is including in their regimen is important when interpreting lab results.  


Ferritin is a biomarker that is the best indicator of iron status in the body. Iron helps support metabolism and form hemoglobin so oxygen can be transported to the tissues, which is important for optimal performance as an athlete. Low iron levels are more common in menstruating female athletes and have been linked to fatigue, higher injury risk, and an elevated resting heart rate. 

Male/Female Hormone Panels

Overtraining, particularly in combination with poor recovery and lack of adequate caloric intake, can result in Relative Energy Deficiency in Sports, or RED-S, which is characterized by a higher risk for injury, illness, and hormone dysfunction, especially in young female athletes. Understanding sex hormone levels can help reduce the risk of RED-S and ensure an athlete's training, recovery, and nutrition align with their performance goals.  

Omega-3 Index

Omega-3 fat levels are important to help keep inflammation from a high training load at bay and have also been linked to better recovery and lower post-training soreness in athletes. The omega-3 index can provide insight into the state of inflammation of an athlete and can help guide recovery plans to support optimal performance.  

Using Labs To Improve Performance in Athletes 

Using the data from functional blood testing, athletes can bring a layer of precision into their nutrition, recovery needs, and any supplements they may need to optimize their performance. 


A nutrition plan with a variety of quality, whole foods that calorically meets the needs of an athlete's training load is an important component of optimal athletic performance. If blood testing indicates deficiencies in specific vitamins or minerals (such as iron or vitamin D), a nutritional plan including more whole food sources of those micronutrients can help ensure the athlete meets their needs.  

Ensuring adequate protein intake is important for athletes, as protein is essential for muscle repair and recovery (training adaptations) and maintaining muscle mass and a favorable body composition. Too little protein may show up as increased injury risk, loss of muscle mass and power, and decreased athletic performance. It may lead to low iron levels, changes in cortisol and sex hormones, and changes in thyroid function since protein is essential for hormone production. Athletes will generally require higher amounts of protein than the recommendations for the general population, with some studies showing up to 2 grams per kilogram of body weight promoting optimal athletic performance.  

Depending on the sport and training load, athletes may need to hit different intakes of carbohydrates for optimal power and performance. While a light recovery day may only require 2-3 grams per kg of body weight, long training days typical of Ironman athletes or other endurance athletes may need three times that amount. A low carbohydrate intake may contribute to changes in muscle strength and power, loss of endurance, and temporary fluctuations in blood labs such as thyroid hormone levels and cortisol.  

Adequate fat intake is also important for athletes, particularly concerning inflammation and hormone production. A moderate fat intake is linked to better testosterone levels, and a higher intake of omega-3 fats helps reduce inflammation and support recovery. Athletes who need to cut their body fat for their sport may consider supplementation with omega-3 fats.


By using functional medicine blood testing as a part of an athletic training program, an athlete can gain personalized insight into what supplements may be needed to support their training and performance goals.  

Blood testing that indicates a high-stress load and overtraining - such as elevated cortisol, low thyroid or other hormone levels, and low levels of micronutrients such as zinc or iron - can translate to a supplement routine that helps support those systems alongside adequate nutrition and an optimal training/recovery split. Adaptogenic herbs such as ashwagandha can be an excellent addition to help support stress levels and optimize performance in these scenarios. 

Some supplements can hinder post-training adaptations - for example, high doses of antioxidant supplements such as vitamin C or E can impact levels of muscle damage that are actually favorable for certain sports, such as bodybuilding. Ultimately a food-first approach to performance nutrition, with supplementation guided by blood work, is the most evidence-led approach for most athletes.  


Blood testing can provide another layer of personalization to an athlete's training, nutrition, and recovery plan to help optimize athletic performance. Leveraging the data in blood tests that look at micronutrients, hormone levels, and markers of inflammation can help ensure an athlete meets their nutritional needs and adequately adapts to their training. It can also help fine-tune nutrition and supplement plans for optimal health. 

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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