The 7 Micronutrients Endurance Athletes Are Often Missing

Everyone’s focused on carbs, protein and fat. But it's the vitamins and minerals underneath all of that which determine whether your body can actually use them. Here's what I see deficient, time and again, in the athletes I work with.

Pip Taylor APD · Sports Dietitian · Former professional triathlete

“Accredited Practising Dietitian, Accredited Sports Dietitian, Masters in Nutrition & Dietetics, IOC Diploma in Sports Nutrition. Former professional triathlete and World #1. I’ve had my own blood panels humble me more than once — and I’ve seen deficiencies quietly derail performance in athletes who were doing everything else right. This piece comes from both experiences.”

Here's something that doesn't get said enough: you can have a textbook macro split, adequate total calories, and a well-timed fuelling strategy — and still be underperforming because of what's happening at the micronutrient level.

I know, because I've been there. A few years into my professional career, I was training hard, eating well by any reasonable standard, and feeling perpetually flat. The kind of flat that isn't explained by overtraining or under-sleeping. The kind that just sits in your legs and your head and doesn't shift. A thorough blood panel told the story: my ferritin was on the floor, my vitamin D was marginal, and my omega-3 index was poor.

Three months of targeted work later, I felt like a different athlete. Not because I'd got fitter. Because I'd finally addressed some micro issues I hadn't been aware of.

"Deficiencies don't usually announce themselves dramatically. They just make everything slightly harder, slightly slower, and slightly less enjoyable — until one day you fix them and wonder where that version of yourself has been."

These are the seven I see most consistently in the athletes I work with. Some might surprise you.

1. Iron

Oxygen transport · Energy metabolism · Immune function

Iron is the deficiency I find most often, and the one most often misread. Standard blood tests measure haemoglobin — but you can have normal haemoglobin and depleted ferritin (iron stores), which is enough to crater your performance. Always ask for ferritin specifically. Female athletes, runners, and plant-based eaters are at highest risk. If you're a runner, foot-strike haemolysis — where the impact of footstrike physically destroys red blood cells in the sole of the foot — is a real additional iron drain that general population guidelines don't account for.

S I G N S O F D E F I C I E N C Y

• ⚑  Persistent fatigue and heavy legs in training

• ⚑  Performance drops at all intensities

• ⚑  Getting sick more often than usual

• ⚑  Poor concentration and brain fog

• ⚑  Pale skin, brittle nails, hair thinning

BEST FOOD SOURCES

• Red meat, lamb, beef, liver and organ meat (highest haem iron)

• Oysters, mussels, tinned sardines

• Chicken liver, dark poultry meat

• Lentils, tofu, spinach + vitamin C

• Fortified breakfast cereals

2. Magnesium

Muscle function · Sleep · Energy production · 300+ enzyme reactions

Magnesium is lost heavily through sweat, which means endurance athletes need significantly more than the general population RDI. The frustrating thing is that serum magnesium levels often look normal even when intracellular levels are low — it's not the most reliable blood marker. If you're ticking multiple symptom boxes, consider a trial of magnesium bisglycinate or glycinate (best absorbed forms) in the evening. The effect on sleep quality alone is often noticeable within a week.

S I G N S O F D E F I C I E N C Y

• ⚑ Muscle cramps and twitching, especially at night

• ⚑  Poor sleep quality and restless legs

• ⚑  Increased anxiety, irritability

• ⚑  Heart palpitations

• ⚑  Reduced exercise tolerance

BEST FOOD SOURCES

• Pepitas (pumpkin seeds) — the standout source

• Dark leafy greens: spinach, silverbeet

• Almonds, cashews, dark chocolate (70%+)

• Avocado, legumes, wholegrains

• Firm tofu

3. Vitamin D

Bone health · Immunity · Muscle strength · Inflammation

I have had more Australian athletes tell me they "definitely can't be vitamin D deficient" than I can count. And I've pulled blood panels on those same athletes and found levels well below optimal. Indoor training, consistent sunscreen use, winter months, and high training loads all reduce vitamin D status — regardless of where you live. Test via a 25-OH Vitamin D blood panel. If your level is below 75 nmol/L, supplement D3 (not D2). This is one of the highest- impact, lowest-cost supplementation decisions most athletes can make.

S I G N S O F D E F I C I E N C Y

• ⚑  Frequent illness, especially upper respiratory

• ⚑  Stress fractures or unexplained bone pain

• ⚑  Muscle weakness and general fatigue

• ⚑  Low mood, particularly through winter

• ⚑  Slow recovery between sessions

BEST FOOD SOURCES

• Oily fish: salmon, sardines, mackerel

• Egg yolk

• Mushrooms exposed to UV/sunlight

• Fortified dairy and plant milks

• Beef liver

4. Vitamin B12

Red blood cell formation · Nerve function · DNA synthesis

B12 is almost exclusively found in animal products, which makes this a critical watch point for vegan and vegetarian athletes — and one I take seriously with every plant-based athlete I work with. The tricky thing is that deficiency develops slowly over months to years, and by the time symptoms appear it can take a long time to reverse. Don't wait for symptoms. If you're plant-based, test it, and if levels are low, supplement with methylcobalamin (the most bioavailable form).

S I G N S O F D E F I C I E N C Y

• ⚑  Deep fatigue and anaemia-like symptoms

• ⚑  Tingling or numbness in hands and feet

• ⚑  Brain fog and memory problems

• ⚑  Mood changes, low-grade depression

• ⚑  Inflamed, smooth tongue

BEST FOOD SOURCES

• Beef, lamb, pork — especially organ meats

• Oysters, clams, mussels, sardines

• Eggs and full-fat dairy

• Vegemite - Nutritional yeast (fortified varieties)

• Fortified plant milks and cereals

5. Zinc

Immunity · Wound healing · Hormonal health · Antioxidant defence

Zinc losses through sweat are significant and consistently underestimated. Plant-based athletes face an additional barrier: phytates in grains and legumes bind zinc and reduce its absorption. The fix is preparation — soaking and sprouting legumes meaningfully improves bioavailability. If you're getting sick frequently despite good sleep and training loads that seem manageable, zinc is worth checking.

S I G N S O F D E F I C I E N C Y

• ⚑  Picking up every cold going around

• ⚑  Cuts and injuries healing slowly

• ⚑  Hair loss or thinning

• ⚑  Loss of taste or smell

• ⚑  Hormonal disruption, low testosterone

BEST FOOD SOURCES

• Oysters — by far the richest source

• Red meat, poultry, pork

• Pumpkin seeds, hemp seeds

• Legumes and chickpeas (with preparation)

• Dairy products and eggs

6. Omega 3 - EPA + DHA

Inflammation · Joint health · Brain function · Recovery

Most Australians — athletes included — have a poor omega-3 index. Plant sources like flaxseeds provide ALA, which the body converts to EPA and DHA at a rate of around 5–10%. That's not enough. Aim for two serves of oily fish per week minimum, and consider a quality fish oil supplement for the rest. Look for Informed Sport certified products to ensure they're free of banned substance contamination. Algae oil is the best option for plant-based athletes — it's where fish get their EPA/DHA from in the first place.

S I G N S O F D E F I C I E N C Y

• ⚑  Joints that feel stiff and inflamed

• ⚑  Recovery that never quite catches up

• ⚑  Dry skin, brittle nails

• ⚑  Low mood or poor concentration

• ⚑  High triglycerides on blood panel

BEST FOOD SOURCES

• Oily fish: salmon, mackerel, sardines

• Tinned sardines (cheap, consistent, underrated)

• Walnuts, flaxseeds, chia seeds

• Hemp seeds, flaxseed oil

• Algae oil — the vegan EPA/DHA source

7. Vitamin C

Collagen synthesis · Immunity · Iron absorption · Antioxidant protection

Vitamin C often gets dismissed — "everyone gets enough." But heavy endurance training increases oxidative stress significantly, and requirements rise accordingly. There's also a practical performance trick here: pairing vitamin C-rich foods with plant-based iron sources dramatically boosts iron absorption. Squeeze lemon over your lentils. Have capsicum with your tofu stir-fry. It's a simple habit with a disproportionate payoff for plant-based and iron-depleted athletes.

S I G N S O F D E F I C I E N C Y

• ⚑  Slow recovery from illness

• ⚑  Tendons and connective tissue that

  take ages to heal

• ⚑  Fatigue out of proportion to training load

• ⚑  Easy bruising

• ⚑  Dry, rough skin

BEST FOOD SOURCES

• Red and yellow capsicum — surprisingly high

• Citrus fruit, kiwifruit

• Broccoli, Brussels sprouts, kale

• Strawberries, guava, papaya

• Tomatoes, leafy greens

Get the Right Blood Tests

The only real way to know where you stand is a blood test — and the standard GP panel often isn't enough. Here's what I recommend requesting:

ASK FOR THESE SPECIFICALLY — THEY'RE OFTEN NOT INCLUDED BY DEFAULT

C O R E P A N E L

→  Full blood count (FBC)

→  Serum ferritin — not just haemoglobin

→  25-OH Vitamin D

→  Vitamin B12 and folate

→  Zinc (serum) and magnesium (serum)

W O R T H A D D I N G

→ Omega-3 Index (EPA + DHA % of RBC fatty acids)

→ CRP — inflammation marker → Thyroid function (TSH, fT4) — often disrupted by underfuelling

→ Transferrin saturation alongside ferritin

If your GP pushes back on ordering all of these, explain your training load and that you're working with a sports dietitian on performance nutrition. Most are very happy to help with that context. And if you want proper interpretation in the context of your training, performance and dietary habits, that's what I do in individual consultations.

The Bottom Line

Micronutrients aren't glamorous. Nobody has ever posted their ferritin level on Instagram. But quietly fixing a subclinical deficiency — one you'd been living with for months without realising — can feel more transformative than any training block you've ever done. The adaptation was there. The fitness was there. You were just running on empty at the cellular level.

Food first, always.

Variety and colour in your diet every day. Blood tests to confirm gaps. Targeted supplementation to fill them. That's the whole framework, and it works.