Iron Deficiency, Energy and Performance: Why Iron Matters For Athletes And How To Improve Absorption

Iron deficiency is one of the most common nutrient deficiencies worldwide, affecting energy levels, training performance, recovery, cognitive function and overall health. In this post I'm going to walk you through the different types of iron, how it is absorbed, the signs of iron deficiency, the impact of caffeine on iron absorption and practical strategies to improve iron status (for the general population, athletes and those with gastrointestinal conditions or bariatric surgery).

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When most people think about performance nutrition they think about carbohydrates, protein or hydration. Iron rarely gets the same attention.

Yet iron is one of the most important nutrients for general health, athletic performance, energy production, cognitive function and recovery. Low iron can leave you feeling fatigued, struggling through training sessions, recovering poorly and wondering why your usual nutrition and training strategies are no longer working.

I witness iron deficiency every week through my work as a Professional Certified Sports Nutritionist. It is one of the most common nutrient deficiencies worldwide, affecting billions of people (myself included) and occurring far more frequently in athletes, menstruating women, individuals with gastrointestinal disorders and those who have undergone bariatric surgery.

So in this article, to better inform you, I'll explore:

• What iron does in the body

• The different forms of iron and related B vitamins

• How iron is absorbed

• The signs and consequences of iron deficiency

• How caffeine affects iron absorption

• Strategies to improve iron status

• Special considerations for gut health and bariatric surgery

• Why athletes have higher iron requirements than the general population

• Ferritin considerations for athletes

Let's dive in...

Why Iron Is Essential for Energy, Health and Athletic Performance

Iron is an essential mineral involved in hundreds of biological processes. Most people understand iron's role in haemoglobin, the protein that carries oxygen in red blood cells. However, its importance extends far beyond that as it is required for:

• Oxygen delivery to muscles and tissues

• Energy production within mitochondria

• Cognitive function and concentration

• Immune health

• Hormone synthesis

• DNA production and cellular repair

• Athletic performance and recovery

Researchers estimate that the human body contains around 3-4 grams of iron, with the majority stored in haemoglobin, myoglobin and ferritin. Iron-containing proteins are involved in hundreds of enzymatic reactions throughout the body.

Even before iron deficiency progresses to anaemia, low iron stores can impair physical performance, mental performance and overall wellbeing.

The Different Types of Iron

Not all iron is absorbed equally. There are two primary forms of dietary iron:

Heme Iron

Heme iron is found exclusively in animal foods and originates from haemoglobin and myoglobin.

Sources include:

• Red meat

• Liver

• Poultry

• Fish

• Shellfish

Heme iron is highly bioavailable, with approximately 15-35% absorbed, making it the most efficient dietary source of iron.

Non-Heme Iron

Non-heme iron is found in:

• Beans

• Lentils

• Tofu

• Nuts

• Seeds

• Wholegrains

• Fortified cereals

• Leafy greens

Absorption is significantly lower and more variable, often ranging between 2-20%. Non-heme iron absorption is heavily influenced by other dietary factors that either enhance or inhibit uptake and those following a plant-focused diet can benefit from further supplementation. This is why total dietary iron intake does not always reflect how much iron the body actually absorbs.

Iron and the B Vitamins: A Powerful Partnership

Iron rarely works alone. Several B vitamins play critical roles in red blood cell production, oxygen transport and energy metabolism.

Vitamin B12 (Cobalamin)

Vitamin B12 is essential for:

• DNA synthesis

• Neurological function

• Red blood cell formation

A deficiency can result in megaloblastic anaemia, fatigue, weakness, numbness and cognitive symptoms.

Sources include:

• Red meat

• Fish

• Eggs

• Dairy products

• Fortified foods

People following vegan diets sometimes struggle to obtain enough through nutrition, and others with gastric complications will struggle with absorption. In these cases, supplementation should be considered.

Folate (Vitamin B9)

Folate is another key nutrient involved in red blood cell formation. Low folate status can lead to anaemia and reduced oxygen carrying capacity.

Sources include:

• Leafy green vegetables

• Legumes

• Citrus fruits

• Fortified grains

• Vitamin B6

Vitamin B6

B6 contributes to haemoglobin synthesis and energy metabolism.

Sources include:

• Poultry

• Fish

• Potatoes

• Whole grains

• Bananas

Because iron, B12, folate and B6 collectively contribute to healthy red blood cell production, deficiencies in any of these nutrients can present with similar symptoms including fatigue, weakness and poor exercise tolerance.

How Iron Is Absorbed in the Body

This is. a little bit science-y so I'll try to keep it fairly simple.

The body has no active mechanism for excreting excess iron so balance is regulated through absorption, which primarily occurs in the first sections of the small intestine;

1. Dietary iron (food/supplements) enters the digestive tract.

2. Ferric iron (Fe³⁺) is converted into the more absorbable ferrous form (Fe²⁺)

3. Iron passes into intestinal cells.

4. Iron is stored temporarily as ferritin or transported into circulation.

5. Transferrin carries iron throughout the body to tissues that require it.

Hepcidin (a hormone) acts as the body's regulator of iron metabolism. When iron stores are low, hepcidin decreases, allowing greater iron uptake. When iron stores are sufficient or inflammation is present, hepcidin levels rise and reduce iron absorption. This is why we often see iron deficiency in cases of extreme stress, depression, obesity, gastrointestinal issues, over-training and under-recovery, all of which cause raised inflammation levels. This impairs iron status even when dietary intake appears adequate; the iron pathway is suppressed by hepcidin.

Iron Deficiency: Symptoms, Causes and Performance Implications

As with all things I observe relating to the body, iron deficiency exists on a spectrum. Initially, iron stores become depleted. Over time, iron availability for tissues decreases. Eventually, iron deficiency anaemia may develop.

Common symptoms to look out for include:

• Persistent fatigue

• Shortness of breath

• Dizziness

• Headaches

• Brain fog

• Poor concentration

• Hair loss

• Cold intolerance / cold extremities

• Bruising

• Restless legs

• Increased susceptibility to illness

• Reduced exercise performance

  
  

Athletes and active individuals may notice declining performance long before anaemia develops. Low ferritin can impair oxygen delivery, mitochondrial function and endurance capacity even when haemoglobin remains within the normal range.

Groups at increased risk include:

• Menstruating women

• Pregnant women

• Adolescents

• Athletes

• Vegetarians and vegans

• Individuals with inflammatory bowel disease

• Coeliac disease sufferers

• Bariatric surgery patients

Caffeine and Iron Absorption: Should You Worry?

For most of us, athletes included, coffee is a delicious non-negotiable part of modern life! However I'd like to highlight that while it can indeed be used as a performance tool, even reducing RPE, caffeine can reduce iron absorption from food and supplementation. Coffee and tea for example, contain tannins (a type of polyphenols) that bind to non-heme iron within the digestive tract.

Research consistently demonstrates that consuming caffeine alongside an iron-containing meal or supplementation can significantly reduce non-heme iron absorption.

The effect is less significant when:

• Iron comes from heme sources such as meat

• Caffeine is consumed away from meals and supplementation

• Overall iron intake is adequate

That said, be careful to not get complacent. If you have low ferritin, iron deficiency or increased iron requirements as an athlete for example, I would advise separating your morning coffee, tea or matcha from iron-rich food and specifically supplementation by approximately 1-2 hours.

Note: High-dose calcium supplement can also impair iron absorption.

What About Vitamin B12?

Evidence suggests that caffeine does not appear to substantially block B12 absorption in the same way it affects non-heme iron. For people without specialised considerations, caffeine is unlikely to be a major contributor to B12 deficiency.

However, heavy caffeine consumption may increase gastrointestinal transit time, potentially affecting nutrient exposure and absorption. If you personally are affected by conditions that interfere with stomach acid production, intrinsic factor production, gastrointestinal disease and bariatric surgery who supplement B12, I'd recommend extra care is taken, adopting the same principles as with iron supplementation. Every little helps.

How to Increase Iron Intake and Improve Absorption with Food

Improving iron status is not simply about eating more iron. It's about increasing both intake and absorption.

Prioritise Heme Iron-Rich Foods:

• Lean beef

• Lamb

• Venison

• Liver

• Sardines

• Oysters

• Mussels

Prioritise Non-Heme Iron Sources

• Lentils

• Chickpeas

• Kidney beans

• Tofu

• Pumpkin seeds

• Fortified breakfast cereals

• Quinoa

• Dark leafy greens

  
  

Pair Iron with Vitamin C. Vitamin C is one of the most effective enhancers of non-heme iron absorption.

Good sources of Vitamin C include:

• Citrus fruits

• Kiwi fruit

• Berries

• Peppers

• Tomatoes

• Potatoes

Adding vitamin C to meals can significantly increase non-heme iron absorption.

Iron Considerations for Gut Issues and Bariatric Surgery

Iron deficiency is extremely common in people with gastrointestinal disorders and post-bariatric surgery because many of the anatomical locations responsible for iron absorption are either damaged, inflamed or altogether bypassed.

Common risk factors include:

• Coeliac disease

• Crohn's disease

• Ulcerative colitis

• Small intestinal bacterial overgrowth

• Gastric bypass surgery

• Sleeve gastrectomy

• Reduced stomach acid production

Following bariatric surgery, reduced stomach acid, lower food intake (literally smaller portions due to limited stomach space) and altered intestinal anatomy can all impair iron absorption and increase deficiency risk. Iron deficiency and anaemia are among the most common long-term nutritional complications after surgery.

If this applies to you, regular monitoring is essential. Blood tests should typically include:

• Ferritin

• Full blood count

• Iron status

• Vitamin B12

• Folate

I have partnered with a premium bloods-analysis provider to offer elite-level testing designed to optimise health and performance.

Dietary intake alone is often insufficient following bariatric procedures. Oral iron supplementation may be necessary, while some people require intravenous iron therapy if oral supplementation is ineffective or poorly tolerated. Because bariatric surgery also reduces intrinsic factor production and alters gastric function, B12 deficiency frequently accompanies iron deficiency and should also be supplemented.

One of my favourite old-school remedies for low iron, which I've taken when needed since childhood and often get my athletes to take for an initial "boost" when iron and B12 levels are low is Floradix liquid tonic. It contains 15mg of ferrous gluconate iron which is highly bioavailable and gentle on the stomach. It also includes vitamin C to boost iron absorption, plus B1, B2, B6, and B12 for energy release.

Iron Requirements for Athletes: Why Active People Are Prone To Deficiency

Athletes and very active people face unique challenges when it comes to maintaining iron status because iron losses can occur through:

• Increased red blood cell turnover

• Inadequate energy intake to meet training needs

• Sweat

• Heavy training

• Dieting down

• Gastrointestinal bleeding

• Foot-strike haemolysis during running

• Menstrual losses

  
  

Research suggests that female athletes, adolescent athletes and endurance athletes are particularly vulnerable, however, strength athletes rely on iron too, as it's involved in energy production, recovery and the oxygen-dependent processes that support muscle growth and performance. During periods of hard training, increased volume and peaking for competition, turnover increases, while phases of dieting down to make weight often reduce overall iron intake, creating a situation where iron stores gradually decline over time.

Maintaining adequate iron stores is just as important as hitting protein and carbohydrate targets. If performance, recovery or energy levels start to dip unexpectedly, iron status is worth investigating alongside the usual nutrition and training variables.

Even without anaemia, low iron stores may impair:

• VO₂ max

• Endurance performance

• Strength

• Recovery capacity

• Training adaptations

• Cognitive performance

Don't wait for anaemia to develop. Pay attention to symptoms and regularly monitor your ferritin, haemoglobin and iron markers.

Practical Athlete Strategies

• Include iron-rich foods daily.

• Pair plant-based iron sources with vitamin C.

• Avoid caffeine around key iron-containing food and supplementation.

• Monitor iron status during heavy training blocks.

• Ensure adequate total energy intake.

• Address gastrointestinal issues promptly.

• Seek professional guidance before starting high-dose supplementation*.

*More isn't always better. Excess iron supplementation can cause gastrointestinal side effects and, in some cases, iron overload. Testing should guide supplementation decisions whenever possible.

Understanding Ferritin: The Iron Marker Every Athlete Should Know

When discussing iron status, ferritin deserves special attention. Ferritin is the body's primary iron storage protein and provides an indication of how much iron is available in your reserves. While haemoglobin measures the amount of iron currently being used to transport oxygen, ferritin helps us understand whether the body's iron stores are becoming depleted.

This is important because ferritin levels often decline before iron deficiency anaemia develops. In other words, an athlete may have "normal" haemoglobin levels and still experience symptoms associated with low iron availability.

Low ferritin is associated with:

• Reduced endurance performance

• Increased fatigue

• Poor recovery

• Reduced training capacity

• Impaired adaptation to training

• Reduced aerobic efficiency

What Ferritin Level Is Optimal?

This is where things become more nuanced. Ever had blood testing through your GP come back as normal, providing no answers to why you feel "off'?

Many laboratories provide a broad "normal" reference range, often considering ferritin levels above 15-30 μg/L as acceptable. However, a value that prevents clinical anaemia is not necessarily the same as a value that supports optimal health and athletic performance. Sports medicine practitioners frequently monitor ferritin more closely than standard clinical practice, particularly in athletes reporting unexplained fatigue, declining performance or difficulty recovering from training.

While there is ongoing debate regarding optimal thresholds, as a Professional Certified Sports Nutritionist, I would consider ferritin levels below approximately 30-50 μg/L, particularly in athletes and menstruating females a bit of a red flag.

Ferritin results should never be interpreted in isolation as it can be affected by inflammation, infection and illness which temporarily elevate levels and potentially mask an underlying iron deficiency. So a full screening is recommended alongside:

• Full blood count (FBC)

• Haemoglobin

• Transferrin saturation

• Serum iron

• C-reactive protein (CRP), where appropriate

The decision to supplement should be guided by blood test results and interpreted within the context of individual symptoms, training load, medical history and dietary intake. The goal should never be to maximise ferritin indiscriminately, but instead; maintain healthy iron stores that support both health and performance.

For athletes undertaking regular training, periodic monitoring of iron markers may be just as important as tracking body composition, recovery or training metrics. After all, even the best training programme cannot compensate for nutritional deficiencies, insufficient oxygen delivery and energy production.

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Key Takeaways

Iron is one of the most important nutrients for health, energy production and athletic performance, yet it remains one of the most common deficiencies worldwide.

For athletes, menstruating women, individuals with gastrointestinal conditions and those who have undergone bariatric surgery, proactive monitoring is especially important.

If fatigue, poor recovery, declining performance or persistent low energy are becoming a recurrent issue, iron status deserves a place on your investigation list... Because the missing piece isn't more caffeine, more motivation or more training. It's simply having enough iron to support the physiology that makes better athletic performance possible.

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Recommended Scientific References

1. Ems T, St Lucia K, Huecker MR. Biochemistry, Iron Absorption. StatPearls, 2023.

2. Bjørklund G et al. Iron Deficiency in Obesity and after Bariatric Surgery. Biomolecules, 2021.

3. Jáuregui-Lobera I. Iron Deficiency and Bariatric Surgery. Nutrients, 2013.

4. ten Broeke R et al. Iron deficiency before and after bariatric surgery: the need for iron supplementation. Neth J Med, 2013.

5. Anvari S et al. Iron supplementation following bariatric surgery: A systematic review of current strategies. Obesity Reviews, 2021.

6. Recent athlete data demonstrate that iron deficiency is common in competitive athletes and is associated with lower VO₂ peak and reduced performance capacity.