Monitoring blood biomarkers may seem reserved for elite athletes, but low levels of vitamins and minerals are common even among amateurs, and can have negative effects on performance.Β As long winter training days approach, now is the best time to proactively get blood work evaluated. In fact, you may already be behind on scheduling yours.
Get a full blood count
Intro to Blood Work
Our Toolbox editor Dr. Stephen Cheung looked at Blood Donation and Training Impact earlier, but here weβll look at how the actual composition of your blood can affect your cycling performance.
Biochemical and hematological testing provides valuable insights into your bodyβs ability to balance training and recovery, and it can indicate when things are going awry. However, one issue many athletes face is simply not getting testing done. Additionally, arbitrary, isolated, or inconsistent testing provides limited information and makes interpretation challenging. Normal blood values vary between non-athletes and athletes, between sports, and even between race and gender. If one of your vitamin or mineral values is off, correcting it can take weeks or even months.
Common Vitamin Deficiencies
Athletes often donβt feel like anything is wrong, but itβs impossible to feel your cellular health status, until problems really start to worsen. Vitamin and mineral deficiencies are common in sports, especially as metabolic stress and training volume increase, or as sleep, life stress, or poor dietary habits take their toll. Some common problem areas for athletes include iron, vitamin D, Omega-3, folate, B-12, magnesium, and calcium.
For endurance athletes, issues with iron and vitamin D status are arguably the most problematic and abundant, so letβs dive deeper into these two nutrients.
Iron
Iron plays an essential role in energy production, as it is involved in oxygen transport and utilization. It is a critical component of hemoglobin in red blood cells, which carries oxygen to working muscles during exercise. Iron also aids mitochondrial energy production.
A lack of iron, whether just low or deficient, can have knock-on effects for health and performance. Symptoms of insufficient or deficient iron include dizziness, lightheadedness, shortness of breath, as well as a decrease in aerobic performance, lower time to exhaustion, increased rate of perceived exertion, and reduced VO2max.
The standard biological range for iron, as with other vitamins and minerals, is based on a general population sample and does not account for athletesβ specific needs. Even athletes who meet the dietary recommendation for iron (13β18 mg/day) may become deficient due to factors that deplete iron stores.
Iron status is influenced by:
- Menstrual bleeding
- Inadequate dietary intake
- Exercise-induced gastrointestinal bleeding
- Loss of blood in urine (hematuria)
- Sweating
- Reduced iron absorption from exercise-induced inflammation
- Red blood cell destruction from repetitive foot strikes
- Increased intramuscular pressure in swimmers and cyclists
- Greater mechanical loading with hepcidin release due to subclinical exercise-related inflammation
Considerations for Supplementation
For accurate testing, itβs important to maintain consistent and controlled conditions to avoid noise in the sample. Testing should ideally be done in the morning, in a hydrated state, avoiding intense or long workouts in the 24 hours prior, and without heavy lifting or eccentric loading 2β3 days before. At a minimum, blood collection and testing should include iron, iron-binding capacity, transferrin saturation, and ferritin levels. If possible, also obtaining serum soluble transferrin receptor, hemoglobin mass, and C-reactive protein would be of further benefit, but likely at an extra cost.
Supplements and dietary adjustments may be needed based on results of blood testing and biomarkers, but blanket supplementation prior to testing is not recommended and may actually be dangerous or contraindicated for certain health conditions and medications. Working with a sports dietitian and physician is key to safely interpreting and acting on test results.
The sun for vitamin D
Vitamin D
Vitamin D, also known as the βsunshine vitaminβ due to its synthesis from UVB rays, is crucial for bone health, muscle function, and immune support, which all play vital roles in performance and recovery. It also helps regulate minerals involved in bone metabolism, like calcium and phosphorus, and enhances immune function to help athletes resist illness.
Prevalence rates for low or deficient vitamin D levels are high, with studies reporting 44β67% or higher depending on various factors.
Vitamin D status is influenced by:
- Aging: Synthesis decreases with age
- Skin pigmentation: Higher melanin levels reduce UVB absorption, slowing synthesis
- Body fat: Excess body fat stores vitamin D, lowering availability
- Sunscreen: High SPF reduces synthesis capacity by over 90%
- Clothing: UV-blocking fabrics inhibit UVB exposure
- Pollution and cloud cover: Ozone and pollutants absorb UVB, reducing synthesis
- Time of day: UVB levels are insufficient in early morning and late afternoon
- Latitude: Locations above 35Β° N or S see reduced synthesis in winter
- Sun avoidance: Limited sun exposure restricts vitamin D production
- Genetics: Some genetic variations affect vitamin D binding or response to supplements
Considerations for Supplementation
Vitamin D levels may not be compromised during summer, depending on factors like clothing, protective equipment, sunscreen use, and time spent outside. Darker-skinned athletes may have lower vitamin D levels without experiencing negative effects on bone mineral density. Putting risk into context is important and may lead athletes to only needing supplementation when one of the above risk factors is elevated, such as during winter or training at certain latitudes.
Similar to iron, vitamin D supplementation and response depends on initial levels along with supplemental dosage provided, and may take 6-12 weeks to course correct. In some cases, physicians prescribe high doses of vitamin D weekly or monthly, while in other cases, an over-the-counter supplement may suffice. Excessive supplementation can actually lower vitamin D levels and even be toxic, so timing and dosage should be guided by blood testing and professional consultation.
Putting a Plan into Action
While iron and vitamin D are common concerns, many athletes also face issues with suboptimal diets, underfueling, limited variety, food allergies, malabsorption from disease, and low micronutrient intake, which often cause these recurrent deficiencies to begin with. Working with a professional can help you address these challenges, making nutritional choices easier and more sustainable.
To monitor blood work and dietary quality, establish a timeline for testing. Seasonal transitions, such as moving from off-season to base training or from base to race season, are ideal times for blood checks. This allows 2β3 check-ins annually to correct issues and adjust nutrition as training focus shifts. Testing of bloodwork for cyclists can be arranged through your physician or directly from companies like InsideTracker, Quest Diagnostics, and LabCorp. Consulting with your physician and a registered dietitian, ideally a Certified Specialist in Sports Dietetics (CSSD), ensures that testing and follow-up actions are both effective and safe.
Now is a good time for a test
References
- Lee, E. C., Fragala, M. S., Kavouras, S. A., Queen, R. M., Pryor, J. L., & Casa, D. J. (2017). Biomarkers in Sports and Exercise: Tracking Health, Performance, and Recovery in Athletes. Journal of strength and conditioning research, 31(10), 2920β2937. https://doi.org/10.1519/JSC.0000000000002122
- Sim, M., Garvican-Lewis, L. A., Cox, G. R., Govus, A., McKay, A. K. A., Stellingwerff, T., & Peeling, P. (2019). Iron considerations for the athlete: a narrative review. European journal of applied physiology, 119(7), 1463β1478. https://doi.org/10.1007/s00421-019-04157-y
- Owens, D. J., Allison, R., & Close, G. L. (2018). Vitamin D and the Athlete: Current Perspectives and New Challenges. Sports medicine (Auckland, N.Z.), 48(Suppl 1), 3β16. https://doi.org/10.1007/s40279-017-0841-9
- Larson-Meyer, E. (n.d.). The importance of vitamin D for athletes. Gatorade Sports Science Institute.https://www.gssiweb.org/sports-science-exchange/article/sse-148-the-importance-of-vitamin-d-for-athletes
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