Vitamins and minerals for athletes: which blood values count

For athletes, five nutrients in your blood matter most: vitamin D, vitamin B12, iron (ferritin), magnesium and zinc. A shortfall in any of them slows your recovery, your energy or your hormone balance, often before you notice it in the gym. The only way to know for sure is a targeted blood test.

I think most athletes guess for too long. You tune your training and nutrition to the gram, yet your micronutrients stay a blind spot. A targeted measurement makes that blind spot visible at once.

Which vitamins and minerals matter for athletes?

For athletes, vitamin D, vitamin B12, iron, magnesium and zinc carry the most weight. They steer your oxygen transport, your muscle function, your recovery and your hormone balance. Other values count too, but these five explain most complaints around energy and performance.

Below you see what each nutrient reveals in your blood and which target value labs in the Netherlands often use. Reference values differ per laboratory, so always read your own result next to that lab range.

What binds these five is that they all act directly on your training response. A deficiency not only slows your recovery, it often lowers the quality of your next session too. That is why they deserve a fixed place in your measurements, alongside the classic values your GP draws by default.

How do you recognise a deficiency?

A deficiency rarely starts with a clear signal. Usually you notice vague complaints: you recover slower, you catch colds more often, or your sessions land just below your usual level. Because those complaints look alike, it helps to link the complaint to a likely deficiency and the right blood value.

This table does exactly that. Treat it as a starting point for the conversation with your doctor, not as a diagnosis.

Watch the pattern, not a single complaint. Only when a symptom coincides with an abnormal blood value does the story become complete.

Which blood values should an athlete test?

A useful base for athletes covers vitamin D, vitamin B12, ferritin, magnesium and zinc. If you really want to steer your performance, you add your hormone status and an inflammation marker. That way you see not only deficiencies, but also how your body responds to your training load.

A standard draw at the GP is aimed at disease, not optimisation. As a result it often misses the very values an athlete can act on. The Netherlands Nutrition Centre notes that a varied diet covers most peoples needs, but athletes with a high load, a strict diet or little sunlight are an exception.

What matters is that you read the values not in isolation but as a coherent picture. A low ferritin next to a low B12 points to a different story than a low ferritin with otherwise fine values. By looking at the markers together you see whether it is an isolated deficiency or a broader nutrition problem.

Compose your own panel through our custom blood test, or start with the broad 360 Health blood test that combines these values.

What does each nutrient do for your performance?

Vitamin D supports your muscle function and immune system, and a low status is common in athletes during winter. A review in Sports Medicine describes how vitamin D does more than steer bones and may be relevant for muscle strength (Owens, 2018). Read on in vitamin D deficiency in athletes.

Vitamin B12 is needed to make red blood cells, and those carry oxygen to your muscles. A deficiency can cause anaemia and stubborn fatigue (Stabler, 2013). More on this in vitamin B12 and energy.

Iron and ferritin determine how much oxygen your blood can carry, and endurance athletes in particular risk low stores. Magnesium plays a role in muscle and nerve function and in your sleep. Dig into iron deficiency in athletes and magnesium for athletes.

Zinc supports your hormone balance and recovery. In men with a proven deficiency, zinc status was linked to testosterone levels (Prasad, 1996). That does not mean extra zinc lifts your testosterone when you already get enough. Read the nuance in zinc and testosterone. If you also want to track your fatty acid status, your omega-3 index is a logical addition.

Strength versus endurance athletes: different accents

Strength and endurance athletes load their bodies differently, and that shows in which values shift first. Endurance athletes lose more iron and run into low ferritin sooner. Strength athletes ask more of their recovery and hormone balance, where zinc and vitamin D play a role.

In endurance athletes, the breakdown of red blood cells adds to the iron drain, the so-called foot-strike effect in running. Your ferritin can fall while your diet is not even poor. A low store undermines your oxygen transport and so your endurance, often before you officially have anaemia.

Strength athletes notice a deficiency earlier as slower recovery and less force. Vitamin D supports your muscle function, and zinc is involved in your hormone balance. Anyone training heavy and frequently structurally asks more of those systems.

That does not mean one group may ignore the others markers. The accent differs, the base stays the same: vitamin D, B12, ferritin, magnesium and zinc.

Timing and season: when your values shift

Your blood values are not a fixed number but a snapshot that moves with the season, your training and your diet. Vitamin D is the clearest example: in the Dutch winter your skin barely makes vitamin D, because the sun sits too low. Many athletes drop to their lowest value of the year between October and March.

So test at a fixed moment, ideally fasted and on a calm day without heavy training before it. A hard session can briefly push markers like CK and cloud your picture. The Dutch National Institute for Public Health notes that vitamin D status in the population is lowest at the end of winter.

The trick is not a perfect snapshot but a repeat measurement. Only when you see the same value in two different seasons do you know whether it is a trend or chance.

For most minerals the timing matters less, but the principle holds: compare like with like by drawing blood at comparable moments.

When do you really need supplements?

A supplement makes sense when a blood test shows a deficiency, or when you belong to a known risk group. If you just add them, you may spend money on values that are already fine, and for some minerals too much works against you. So the order is: measure first, then adjust.

Vitamin D is partly an exception, because many people make less of it in winter. The Dutch Health Council advises extra vitamin D for certain groups. For most other nutrients, proving a deficiency before you supplement is smarter than guessing.

My advice: treat your blood values as a dashboard, not a diagnosis. You discuss a deviation with your doctor, but the trend across the seasons is yours to keep an eye on.

Common mistakes when testing yourself

The biggest gain often is not an extra marker, but avoiding a few standard mistakes. Athletes who track their values seriously usually run into the same traps.

The first mistake is supplementing on a guess. You read that magnesium is good for recovery and add it for months, without ever measuring whether your value was low. That still tells you nothing about your real status.

The second mistake is overrating a single measurement. One result is a snapshot that moves with your training, your fluid balance and the season. Only a trend across several measurements tells the real story.

A third mistake is looking only at serum values for minerals like magnesium. Most of it sits in your cells and bones, so a normal serum does not fully rule out a deficiency. Always read your result together with your complaints.

The fourth mistake is drawing blood right after a hard session. Markers like CK then spike and colour your picture. Plan your measurement on a calm day, and you compare like with like.

Frequently asked questions

Below are the questions I get back most from athletes checking their micronutrients for the first time.

How often should you test your vitamins and minerals? For most athletes once or twice a year is enough, for example at the end of winter and in summer. If you spot a deficiency and adjust, a retest after a few months shows whether your approach works.

Can you fix a deficiency with food alone? Often yes, as long as your diet is varied and misses no whole food groups. With a proven and stubborn deficiency, or a strict diet such as vegan eating, a supplement after advice can help.

Do multivitamins give the same insight as a blood test? No. A multivitamin tops up without you knowing what you lack, while a blood test shows which value is actually low. Measuring stays more precise than broad supplementing.

Can too much of a vitamin or mineral be harmful? For fat-soluble vitamins and some minerals, too high an intake can be unfavourable. That is exactly why measuring first and then adjusting is smarter than guessing high.

References

1. Owens DJ, Allison R, Close GL. Vitamin D and the Athlete: Current Perspectives and New Challenges. Sports Medicine. 2018;48(Suppl 1):3-16. PMID: 29368183.
2. Stabler SP. Clinical practice. Vitamin B12 deficiency. New England Journal of Medicine. 2013;368(2):149-160. PMID: 23301732.
3. Prasad AS, Mantzoros CS, Beck FW, Hess JW, Brewer GJ. Zinc status and serum testosterone levels of healthy adults. Nutrition. 1996;12:344-348. PMID: 8875519.
4. Gezondheidsraad. Dietary reference values for vitamin D. Accessed 2026.
5. Netherlands Nutrition Centre (Voedingscentrum). Vitamins and minerals. Accessed 2026.
6. RIVM. Vitamin D status in the Dutch population. Accessed 2026.

Disclaimer

Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. A blood test is a tool to walk into the conversation with your GP better informed, not a diagnosis in itself. For treatment decisions, discuss your results with your GP.