Why You Should Get Your Blood Work Done — Now

Alex Winnicki
Oct 28
4 min read

As race season winds down and the days start getting shorter, many athletes begin to shift gears — recovering, rebuilding, and refocusing. But this is also the time of year when supplement habits tend to ramp up.Iron. Vitamin D. Omega-3s. Magnesium. The list goes on.

A lot of athletes start taking new products as an “insurance policy,” assuming more is better or that a little extra can’t hurt. The problem is, that’s not always true. Some supplements can be contraindicated with medications or health conditions, meaning you could unintentionally interfere with prescriptions, make them less effective, or put yourself at risk of side effects.

That’s why I’m a strong believer in testing, not guessing.

You can’t know what your body needs until you look under the hood.

The Role of Blood Work

Monitoring blood biomarkers may seem like something reserved for elite athletes, but low vitamin and mineral levels are common even among recreational and competitive amateurs. As long winter training blocks approach, now is the ideal time to get your blood work checked.

Biochemical and hematological testing gives insight into how well your body is balancing training, recovery, and overall health. But too often, athletes don’t test at all — or only get isolated results that don’t paint the full picture.

“Normal” lab ranges are built on general populations, not endurance athletes. And because blood markers shift slowly, correcting a deficiency can take weeks or months. That’s why consistent, strategic testing matters.

Vitamin D: The Sunshine Vitamin (That Fades Fast)

Vitamin D often becomes the most relevant nutrient this time of year. As sunlight fades, your body’s ability to make vitamin D from UVB exposure declines sharply — especially above 35° latitude, where winter sunlight is too weak for synthesis. Vitamin D supports bone health, muscle function, immune regulation, and even mood stability. Low levels are linked with higher injury risk, poor recovery, and increased illness during heavy training.

Common Factors That Lower Vitamin D

Aging (skin converts less vitamin D over time)
Higher skin pigmentation (melanin reduces UVB absorption)
Excess body fat (stores vitamin D, lowering circulating levels)
Clothing, sunscreen, and indoor training
Pollution, cloud cover, and limited sun angles in fall/winter

Deficiency rates in athletes often exceed 40–60%. The good news is that with proper testing, you can identify low levels and correct them in a matter of weeks.

Why You Should Test First

It’s tempting to start supplementing “just to be safe,” but excessive vitamin D can cause toxicity, calcium imbalance, and other issues. While these issues may not be common among vitamin D consumers, the same cannot be said for other types of supplements and thus I think it's a good principal to be safe and not sorry. Testing gives you a baseline to personalize dosage and timing, typically over a 6–12-week period guided by your dietitian. Don't take medical decision into your own own without consultation.

Iron: The Oxygen Carrier

Iron is another nutrient where athletes often struggle — and guess. It’s essential for oxygen transport, energy production, and endurance performance. Even a mild deficiency can lower VO₂ max, raise perceived exertion, and limit recovery.

Iron status can be influenced by:

Menstrual blood loss
Inadequate intake or vegetarian diets
GI bleeding from long-term endurance training
Sweat losses and inflammation
Red blood cell destruction from running

Testing should ideally include iron, ferritin, transferrin saturation, and total iron-binding capacity. Additional markers like CRP or soluble transferrin receptor can provide a clearer picture. As with vitamin D, supplementing before knowing your baseline can backfire — iron overload is just as harmful as deficiency.

The Risk of Blind Supplementation

It’s easy to see supplements as a shortcut — but they’re not risk-free. Beyond contraindications with medications, some nutrients compete for absorption, or can mask symptoms of larger issues. That’s why I recommend consulting with a registered dietitian before starting anything new. Together, you can decide what’s worth testing, interpret results in context, and build a plan that supports your health and performance.

At Second Arrow Nutrition, we use Fullscript to help athletes order only what they need — high-quality supplements à la carte — and avoid wasting money or taking unnecessary risks. If needed, you can schedule affordable, out-of-pocket blood tests through LabCorp or Quest Diagnostics. You’ll see a phlebotomist on your own schedule, and results are typically available within 1–3 days. From there, your dietitian can walk through results, determine appropriate dosing, and adjust your nutrition plan accordingly.

Putting It Into Context

In my own recent blood work, my total cholesterol came back at 204 mg/dL — technically “high.” But when you look deeper — high HDL, low triglycerides, and favorable ApoB — there was no cause for concern or major dietary changes yet, but the higher HDL warrants a few follow up questions. That’s why data matters. Context changes everything.

For one athlete, that same number could indicate cardiovascular risk. For another, it’s perfectly fine. The key is understanding what’s normal for you.

Takeaway

As we transition into shorter days and longer training blocks, it’s worth taking the same precision you bring to your workouts and applying it to your health.

Test before you supplement.
Consult before you guess.
Use data to drive decisions.

Supplements can be powerful tools — but they’re only as effective as the strategy behind them.

Food first. Not food only. Test, don’t guess.

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), 2920–2937. 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), 1463–1478. 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), 3–16. 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