One of the questions I receive most often from readers isn’t about hormones.
It’s about exhaustion.
People tell me they wake up tired despite sleeping eight hours. They can’t concentrate at work. Their workouts feel harder than they used to. Their hair seems thinner, they’re constantly cold, and somewhere along the way, their interest in sex quietly disappeared.
Most assume it’s stress. Others blame ageing, burnout, or changing hormones. And while all of those can absolutely play a role, there’s another possibility that’s surprisingly easy to overlook.
Iron.
Not because iron is a miracle nutrient, and certainly not because every case of fatigue or low libido can be explained by a deficiency. But because iron deficiency remains the most common nutritional deficiency in the world, affecting an estimated two billion people.¹ Even more surprising is how often it goes undiagnosed—not because people don’t have symptoms, but because those symptoms develop so gradually that they begin to feel normal.
You don’t wake up one morning suddenly exhausted.
Instead, your afternoon energy starts dipping. Climbing stairs feels slightly harder than it used to. Your usual gym session leaves you unusually breathless. You become increasingly dependent on caffeine. Your hairbrush collects a little more hair each week. You lose interest in things you previously enjoyed—including sex—but it’s easy to blame a stressful job or simply getting older.
For many people, these changes happen so slowly that they never think to question them.
Then someone orders a blood test.
Ask someone what iron does, and the answer is usually immediate.
“It helps make blood.”
That’s true—but it’s only a small part of the story.
Iron is involved in hundreds of biochemical reactions throughout the body.² One of its most important jobs is helping haemoglobin inside red blood cells transport oxygen from the lungs to every tissue that needs it. Every heartbeat delivers oxygen to your muscles, brain, heart, liver, and every other organ. Without enough iron, that delivery system becomes progressively less efficient.
But oxygen transport is only one piece of the puzzle.
Iron is also essential for producing cellular energy. Deep inside almost every cell sit tiny structures called mitochondria—often described as the body’s powerhouses. They convert nutrients from the food we eat into adenosine triphosphate (ATP), the molecule that powers virtually every biological process. Iron-dependent enzymes play a central role in this system, meaning that when iron stores begin to fall, the body quite literally becomes less efficient at producing energy.³
That helps explain why fatigue is often the earliest symptom of iron deficiency. It’s not simply that you’re carrying less oxygen. Your cells are also becoming less effective at turning that oxygen into usable energy.
Iron also contributes to normal immune function, DNA synthesis, muscle metabolism, and the production of several neurotransmitters, including dopamine, which influences motivation, reward, and mood.⁴
When you appreciate just how many systems rely on iron, it becomes much easier to understand why a deficiency can affect far more than your blood count.
Here’s where things become particularly interesting.
Most of us have been taught that iron deficiency and anaemia are essentially the same thing.
They’re not.
Anaemia is the end result of prolonged iron deficiency—not necessarily the beginning.
Before haemoglobin starts falling, the body first draws upon its iron stores. These reserves are stored primarily in a protein called ferritin.⁵ Think of ferritin as your savings account. When your dietary intake doesn’t meet your body’s needs—or when you’re losing more iron than you’re replacing—you begin spending those savings.
Only later, once those reserves become depleted, does haemoglobin begin to fall enough to meet the definition of iron deficiency anaemia.
This means it’s entirely possible to have normal haemoglobin while your iron stores are already running low.
And that’s exactly where many people find themselves.
Several studies have shown that iron deficiency without anaemia can still be associated with fatigue, impaired cognitive performance, reduced exercise capacity, and poorer quality of life.⁶ ⁷ In fact, some people begin experiencing symptoms months before their routine blood tests would ever label them as anaemic.
That’s one reason many clinicians now look beyond haemoglobin alone when investigating unexplained fatigue, particularly in women.
Iron deficiency can affect anyone, but women shoulder a disproportionate share of the burden.
The most obvious reason is menstruation.
Every menstrual cycle involves blood loss, and with blood comes iron. For women with heavy menstrual bleeding, those monthly losses can gradually exceed what diet alone replaces.⁸ Pregnancy places even greater demands on iron stores because iron is required not only for the mother’s expanding blood volume but also for the developing fetus and placenta.⁹
Diet can add another layer.
Vegetarians and vegans can absolutely maintain healthy iron levels, but the form of iron found in plants—non-haem iron—is absorbed less efficiently than the haem iron found in meat, poultry, and seafood.¹⁰ That doesn’t make deficiency inevitable, but it does make dietary planning more important.
Endurance athletes represent another high-risk group. Repeated foot-strike during running, increased iron losses through sweat, gastrointestinal bleeding during prolonged exercise, and greater physiological demand all contribute to higher iron requirements.¹¹ Female endurance athletes are particularly vulnerable because they often combine several of these risk factors simultaneously.
Although iron deficiency is far less common in men, it’s by no means impossible.
The difference is that when an adult man develops iron deficiency, doctors usually become much more interested in why.
Unlike menstruating women, men don’t routinely lose blood. That means iron deficiency often prompts a search for an underlying cause, such as bleeding from the stomach or intestines, coeliac disease affecting nutrient absorption, inflammatory bowel disease, or, in some cases, colorectal cancer.¹²
That’s why iron deficiency in men should never simply be treated with supplements without first understanding what’s causing it.
Finding the cause is often just as important as correcting the deficiency itself.
At first glance, not very much.
Iron isn’t a sex hormone. It doesn’t directly regulate desire in the way oestrogen or testosterone do.
And yet, when researchers study sexual wellbeing, they consistently find that it depends on far more than hormones alone.
Desire requires energy.
It requires good sleep.
It requires a brain that isn’t struggling through constant fatigue or brain fog.
It requires motivation, mood, and the physical capacity to enjoy intimacy.
Iron influences every one of those systems.
That doesn’t mean low iron directly causes low libido. The evidence simply isn’t strong enough to make that claim.
But it does mean that if iron deficiency leaves you exhausted, mentally drained, sleeping poorly, exercising less, and feeling generally unwell, it’s not difficult to understand why your interest in sex might quietly fade as well.
And that’s exactly what we’ll explore. We’ll look at what the research says about iron deficiency and sexual health in both women and men, why correcting iron deficiency sometimes improves quality of life far beyond energy levels, and what you can do if you suspect your iron stores may be running low.
If you’ve made it this far, you might be wondering one obvious question.
If iron is involved in energy production, oxygen transport, brain function, and hormone regulation, could simply correcting an iron deficiency improve someone’s libido?
The answer is: sometimes, yes—but it’s rarely that straightforward.
One of the biggest mistakes we make when talking about sexual desire is assuming there’s a single “libido hormone” or one biological switch that turns desire on and off. In reality, libido is one of the most complex behaviours in the human body. It’s influenced by sleep, stress, relationship quality, hormones, medications, mental health, chronic illness, nutrition, and overall energy availability. Iron is simply one piece of that much larger puzzle.
That said, it’s a surprisingly important piece.
When researchers study iron deficiency, they repeatedly find that many of the symptoms people report—persistent fatigue, reduced physical endurance, poor concentration, lower motivation, depressed mood, and cognitive fog—are themselves well-established contributors to reduced sexual desire. Iron deficiency doesn’t necessarily reduce libido directly. Instead, it creates an internal environment where the body prioritises survival over reproduction. From an evolutionary perspective, this makes perfect sense. When energy resources are limited, investing in essential functions becomes far more important than sexual behaviour.
This isn’t unique to iron deficiency. We see the same pattern during illness, prolonged sleep deprivation, chronic stress, and undernutrition. Libido often becomes one of the first things the body quietly places on the back burner.
One of the biggest surprises while researching this topic wasn’t discovering that iron can influence libido.
It was realising how many people may be living with low iron without ever considering it as the cause of how they feel.
Iron deficiency doesn’t usually announce itself dramatically. There’s rarely a moment when you wake up and think, “I must be iron deficient.” Instead, the changes tend to creep in slowly. You feel a little more tired than usual. Your workouts become harder. You start relying on another cup of coffee to get through the afternoon. Your interest in sex quietly fades. None of these changes are dramatic enough on their own to raise alarm, which is precisely why iron deficiency is so easy to overlook.¹⁰
Because these symptoms develop gradually, they’re often blamed on everything else first. We tell ourselves we’re working too much, sleeping too little, getting older, or simply feeling the effects of a busy life. Sometimes that’s true. But sometimes the body is trying to tell us something much simpler.
Iron deficiency rarely presents with just one symptom. Instead, it’s usually a collection of small changes that seem unrelated until you step back and look at the bigger picture.
You may want to speak to your healthcare provider if you’ve noticed several of the following over the past few months:
Persistent fatigue that doesn’t improve with rest
Difficulty concentrating or persistent brain fog
Hair shedding that’s noticeably increased
Shortness of breath during routine activities
Feeling unusually cold compared to others
Frequent headaches
Restless legs, particularly in the evening
Brittle nails
Reduced exercise performance
Lower libido
Difficulty becoming aroused despite wanting intimacy
Fewer morning erections or reduced sexual desire in men
Heavy menstrual periods
Craving ice or non-food items (known as pica)
None of these symptoms automatically mean iron deficiency. They can also occur with thyroid disease, vitamin B12 deficiency, depression, chronic stress, poor sleep, and many other medical conditions. But when several occur together—particularly in someone with known risk factors—they’re worth investigating rather than dismissing.¹¹ ¹²
One misconception I had before researching this topic was that iron deficiency and anaemia were basically the same thing.
They’re not.
Anaemia is one possible consequence of iron deficiency, but it usually develops later. Before that happens, your body’s iron stores gradually become depleted. Researchers increasingly recognise that people can experience symptoms while their haemoglobin remains within the normal range—a condition often referred to as iron deficiency without anaemia. Studies have shown that treating iron deficiency in these individuals can improve fatigue and quality of life, particularly among women.¹³ ¹⁴
That means a routine blood test isn’t always the whole story.
If iron deficiency is suspected, clinicians often look beyond haemoglobin alone and assess ferritin, which reflects the body’s iron stores, alongside transferrin saturation and other iron studies. Looking at these markers together provides a much clearer picture than relying on a single number.¹⁵
Whenever nutrition becomes a popular topic online, supplements are never far behind.
Iron is no exception.
Scroll through social media for long enough and you’ll eventually find someone recommending iron tablets for fatigue, hair loss, or low libido.
The reality is more complicated.
Unlike many vitamins, excess iron isn’t simply flushed out by the body. Too much iron can accumulate over time and cause damage to organs such as the liver and heart, particularly in people with inherited conditions like haemochromatosis.¹⁵
More importantly, low iron isn’t a diagnosis—it’s a clue.
The real question is why your iron is low in the first place.
For many women, the answer may be heavy menstrual bleeding, pregnancy, postpartum recovery, or conditions such as fibroids and endometriosis.¹⁶
For men—and for women after menopause—iron deficiency deserves even closer attention because it may signal gastrointestinal bleeding, coeliac disease, inflammatory bowel disease, stomach ulcers, or other conditions that require medical evaluation rather than simply replacing iron.
That’s why the goal shouldn’t be to take more iron.
The goal should be to understand what’s causing the deficiency.
If testing confirms that your iron stores are low, treatment should be tailored to the underlying cause. For some people, improving dietary intake is enough. Others may require iron supplements, intravenous iron, or treatment for the condition that’s causing iron loss.
Food still matters.
Heme iron, found in meat, poultry, and seafood, is absorbed more efficiently than non-heme iron from plant foods. But people following vegetarian or vegan diets can absolutely meet their iron requirements with thoughtful planning. Pairing iron-rich foods like lentils, beans, tofu, spinach, and fortified cereals with vitamin C-rich foods helps improve absorption.
It’s also worth remembering that tea and coffee can reduce iron absorption when consumed alongside meals. Simply leaving an hour or two between meals and your favourite cup of tea or coffee may help maximise how much iron your body absorbs.
If supplements are prescribed, newer research suggests that alternate-day dosing may improve absorption while reducing gastrointestinal side effects such as nausea and constipation compared with daily supplementation.¹⁹ That’s one reason treatment plans are increasingly becoming more individualised.
If you’re concerned about your iron levels—or simply want to support them over the long term—here are a few evidence-based habits worth paying attention to.
You’re at higher risk of iron deficiency if you:
Have heavy menstrual periods
Are pregnant or recently postpartum
Follow a vegetarian or vegan diet
Donate blood regularly
Have coeliac disease, inflammatory bowel disease, or other conditions affecting absorption
Participate in endurance sports
Have a history of low ferritin or anaemia
Recognising your risk is often the first step toward getting tested rather than waiting until symptoms become severe.
Include a mix of:
Heme iron (more easily absorbed):
Lean red meat
Chicken
Turkey
Fish
Shellfish
Non-heme iron (plant sources):
Lentils
Chickpeas
Beans
Tofu
Spinach
Pumpkin seeds
Fortified breakfast cereals
Vitamin C can significantly improve the absorption of non-heme iron.
Good combinations include:
Lentils + tomatoes
Spinach + lemon juice
Beans + bell peppers
Fortified cereal + berries
Tofu + broccoli
Tea and coffee contain compounds that reduce iron absorption.
If possible, enjoy them at least 1–2 hours before or after iron-rich meals instead of alongside them.
If you’ve been experiencing:
fatigue,
hair shedding,
brain fog,
reduced exercise performance,
or a noticeable drop in libido,
don’t assume it’s “just stress.”
Ask your healthcare provider whether iron studies are appropriate.
A normal haemoglobin doesn’t always mean your iron stores are adequate.
Depending on your symptoms, your clinician may also assess:
Ferritin
Transferrin saturation
Serum iron
CBC
Iron supplements should ideally follow testing.
Too little iron is harmful.
Too much iron can also be harmful.
Finding out why iron is low is just as important as replacing it.
That might mean addressing:
heavy menstrual bleeding,
poor dietary intake,
pregnancy,
gastrointestinal blood loss,
or an absorption disorder.
Iron stores don’t recover overnight.
Even after treatment begins, it often takes weeks to months for ferritin levels to rebuild and symptoms such as fatigue or reduced exercise tolerance to improve.
Consistency matters far more than quick fixes.
The goal isn't to chase a higher ferritin number. It's to give your body the resources it needs to function at its best—including your energy, your brain, and yes, your libido.
The biggest lesson I took away from researching this topic wasn’t really about iron.
It was about libido.
We often think of sexual desire as something that exists in isolation—as though it’s controlled by a single hormone or switched on by the right supplement.
The reality is far more interesting.
Libido reflects the health of the whole system.
When your body is well rested, well nourished, physically active, and has the resources it needs, sexual desire often follows naturally. When those resources become limited—whether because of chronic illness, poor sleep, persistent stress, thyroid disease, nutritional deficiencies, or iron deficiency—your body quite reasonably starts directing its energy elsewhere.
Seen through that lens, low libido isn’t always the problem.
Sometimes it’s the symptom.
And that’s perhaps the biggest shift I’d encourage you to make after reading this newsletter.
Instead of asking, “How do I increase my libido?” try asking a different question first.
“Is my body missing something it needs to function well?”
For some people, the answer will be hormones.
For others, it may be relationship stress, medication, or mental health.
And for millions of people around the world, particularly women of reproductive age, it may simply be iron.
Sometimes improving sexual wellbeing doesn’t start with a new supplement or a better sex tip.
Sometimes it starts with understanding what your body has been trying to tell you all along.
¹ Camaschella C. Iron Deficiency. New England Journal of Medicine. 2015.
² Camaschella C. Iron-Deficiency Anemia. New England Journal of Medicine. 2015.
³ Tolkien Z, Stecher L, Mander AP, Pereira DIA, Powell JJ. Iron deficiency without anaemia: a diagnosis that matters. Clinical Medicine. 2021.
⁴ World Health Organization. Anaemia.
⁵ National Institutes of Health Office of Dietary Supplements. Iron Fact Sheet for Health Professionals.
⁶ American Gastroenterological Association. Guidelines on Gastrointestinal Evaluation of Iron Deficiency Anemia.
⁷ Houston BL, et al. Efficacy of iron supplementation on fatigue and physical capacity in non-anaemic iron-deficient adults. BMJ Open. 2018.
⁸ Andrews NC. Disorders of Iron Metabolism. New England Journal of Medicine. 1999.
⁹ Hallberg L, Hulthén L. Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron. American Journal of Clinical Nutrition. 2000.
¹⁰ World Health Organization. Anaemia.
¹¹ Camaschella C. Iron deficiency. New England Journal of Medicine. 2015;372:1832–1843.
¹² McClung JP, Murray-Kolb LE. Iron nutrition and premenopausal women: effects of poor iron status on physical and neuropsychological performance. Annual Review of Nutrition. 2013.
¹³ Krayenbuehl PA, et al. Intravenous iron for the treatment of fatigue in non-anaemic, premenopausal women with low serum ferritin. Blood. 2011.
¹⁴ Favrat B, et al. Evaluation of intravenous iron for fatigue in non-anaemic iron-deficient women. Blood. 2014.
¹⁵ World Health Organization. WHO Guideline on Use of Ferritin Concentrations to Assess Iron Status in Individuals and Populations. 2020.
¹⁶ American College of Obstetricians and Gynecologists. Practice Bulletin: Anemia in Pregnancy. 2021.
¹⁷ Beard JL, Connor JR. Iron status and neural functioning. Annual Review of Nutrition. 2003.
¹⁸ Camaschella C. Iron deficiency. Blood. 2019.
¹⁹ Stoffel NU, et al. Iron absorption from supplements is greater with alternate day than consecutive day dosing in iron-deficient women. The Lancet Haematology. 2017.
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