«Nothing really serious has been found. But I am no longer the person I was three years ago.»
It is something we often hear in consultation. The person brings folders of blood tests and scans; almost everything is within the reference ranges. And yet something has changed: they tire sooner, recover worse, sleep without feeling rested and find it hard to concentrate in the afternoon.
Persistent fatigue is one of the most common reasons people see a doctor. It is also one of the most difficult, because it rarely has a single cause. It is not «all in the head», but it is not always solved by finding a single abnormal value either.
Besides sleep, stress and metabolism, we are also interested in the immune system, the microcirculation and the ability of the mitochondria to produce energy.
Fatigue is a symptom, not a diagnosis
The word «tiredness» covers very different experiences. Telling them apart is the first step towards knowing where to look:
Sleepiness
You struggle to stay awake during the day. It usually points to sleep: insomnia, too few hours or apnoea.
Lack of physical energy
Effort costs more. It may be related to anaemia, the thyroid, metabolism or cellular energy production.
Mental exhaustion
Poor concentration or motivation. It may come with stress, mood problems or inflammatory processes.
Fatigue after exertion
A small effort leaves you drained for hours or days. Post-exertional malaise calls for caution.
First, what is common and treatable
Before looking for complex explanations, the common causes have to be ruled out. Many are picked up with a careful medical history and well-targeted blood tests:
- Anaemia and iron deficiency: even without anaemia, an iron deficiency can cause fatigue.
- Thyroid and glucose: an underactive thyroid or undiagnosed diabetes can show up as a lack of energy.
- Sleep: too little sleep, insomnia or sleep apnoea that goes unnoticed.
- Mood: depression and anxiety are also expressed through the body.
- Medicines and alcohol: some medicines and alcohol affect energy and sleep.
- A recent infection: recovery can take weeks or months; in some cases an immune disturbance persists.
- Nutrition and training: eating less than you burn, or training too hard without recovering.
Signs that cannot wait
Probably passing
After a demanding period, little sleep or a mild infection; it clearly improves within one or two weeks.
Ask for an assessment
It lasts more than a month, gets in the way of your life, sleep does not restore you or you feel worse for days after exertion.
See a doctor soon
Weight loss, fever, night sweats, bleeding, swollen glands or new neurological symptoms.
Urgent care
Sudden chest pain or marked difficulty breathing require urgent care.
If fatigue comes with thoughts of harming yourself, ask for help today: in Spain you can call 024, free and available 24 hours a day.
When everything comes back «normal»
This is where the most interesting part begins, and the one that causes the most frustration. Many people have ruled out the common causes and still feel the same. Does that mean nothing is wrong?
Not necessarily. The body has an enormous capacity to compensate: the heart beats a little faster, hormones mobilise energy, the sympathetic nervous system keeps performance going. The tests stay within range. But compensating uses up resources.
When that state lasts for months, the compensation itself can become part of the problem. Science calls it allostatic load. Fatigue may be the signal of a regulatory network that has lost its flexibility.
The immune system: when our defences use up energy
Our immune system needs energy to work. In persistent immune activation, inflammatory mediators such as some interleukins and TNF-alpha can act on the brain, metabolism and the feeling of exhaustion.
That is why, in some inflammatory, autoimmune or post-infectious conditions, fatigue can be one of the main symptoms, even without fever or obvious signs of infection.
The microcirculation: when oxygen does not arrive as it should
Having oxygen in the blood is not enough: it also has to reach the tissues through the smallest blood vessels. Inflammation can affect the vascular endothelium and the regulation of circulation and clotting.
In certain post-infectious conditions, including post-COVID syndrome, microvascular and clotting changes that could contribute to fatigue are being studied. This does not mean that everyone who is tired has microclots or a clotting disorder.
The mitochondria: our power stations
Inside our cells are the mitochondria. They turn nutrients into usable energy, mainly in the form of ATP. To work, they need oxygen, nutrients and a suitable metabolic environment.
Persistent inflammation, oxidative stress and certain metabolic changes can alter how they work and contribute to weakness, exercise intolerance or slow recovery. However, these symptoms alone do not prove mitochondrial dysfunction.
The immune system influences circulation and metabolism. The microcirculation delivers oxygen and nutrients. And the mitochondria supply energy to the cells, including the immune cells.
As well as asking which organ is damaged, it is worth asking which regulatory networks have stopped working properly.
What not to do
Compensating with more of the same
More coffee, more training, fewer calories and catching up on sleep at the weekend. It may work for a while and then make things worse. When there is post-exertional malaise, increasing physical activity indiscriminately can worsen the symptoms.
Taking supplements blindly
Taking iron, vitamins or «energy boosters» without testing may do nothing, mask a problem or, in the case of iron, be harmful.
Resigning yourself
«It must be age» or «it's stress» are not good enough explanations when fatigue is changing your life. It deserves a structured assessment.
How we approach it at ETRYUM
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01
The timeline
When it started and what changed before: an infection, a bereavement, a change of job, more training, less sleep. Also whether there is exercise intolerance or very slow recovery.
-
02
Ruling out
The common and the serious, with an examination and blood tests targeted to the case. When there are clinical clues, assessing inflammation, immunity, vascular function or metabolism.
-
03
Measuring function
When indicated: body composition, cardiovascular and autonomic function, physical capacity, sleep, recovery and metabolic markers. Additional tests are chosen for their usefulness and clinical validity.
-
04
Prioritising
What weighs most in your case and where to start: sleep, available energy, tolerable activity and, when they are identified, metabolic or inflammatory factors.
-
05
Measuring again
Checking what has changed, not only in the blood tests but in energy, sleep, exercise tolerance and the capacity to recover.
An example to make it clearer
Illustrative case
Miguel, 52
Ten years ago he ran half marathons. He works long hours, sleeps about six hours, travels often and still trains hard several times a week. Little by little he recovers worse, his resting heart rate has gone up, he sleeps badly after training, his colds last longer and he finds it hard to concentrate in the afternoon.
He also remembers that after a significant respiratory infection he never fully regained his previous physical capacity. No single finding seems serious. He compensates: more coffee, more training, less food. For a while it works. Then it stops working.
Once relevant medical causes have been ruled out, we do not simply put it all down to stress. We assess whether there are signs of persistent inflammation, changes in cardiovascular regulation or difficulties in how energy metabolism adapts to exertion.
The plan does not start by adding treatments indiscriminately but by putting things in order: protecting sleep, matching activity to his tolerance, eating enough and addressing the metabolic or inflammatory factors identified. And, a few months later, measuring again.
The question was not only which value was abnormal, but what had stopped regulating properly in his body.
To finish
Persistent fatigue deserves to be listened to. Sometimes it has a specific, treatable cause. At other times it is the expression of a body that has been compensating for too long, or of an interaction between our defences, circulation and energy metabolism.
Tell the type of fatigue apart. Rule out the common and the serious. Understand the network. Put things in order before adding. And check what changes.
Health is not a perfect state that you either have or do not have. It is the capacity to adapt and return.
This article is for general information and does not replace an individual medical assessment.
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