You do not bounce back from a hard session like you used to. Your legs feel heavy on the stairs. By mid-afternoon your brain is running on fumes, and no amount of coffee fixes it. Is it your mitochondria?
It is a fair question, and the internet is full of confident answers. Here is a clearer one. I will explain the signs that get linked to poor mitochondrial function, why those signs are not specific, what a doctor should rule out first, when something more serious deserves a specialist, and what actually helps in everyday life.
Key takeaways
- Common signs linked to low cellular energy include persistent fatigue, muscle weakness or heaviness, slow exercise recovery and brain fog. These signs are not specific, and most people with them do not have a mitochondrial disorder.
- Many everyday causes of tiredness are treatable and should be checked first, including low iron, low B12, thyroid problems, sleep apnoea, depression and medication effects.
- True mitochondrial disease is a rare genetic condition. Warning signs include unexplained muscle weakness, eye muscle problems, hearing or vision loss, or a family history on your mother's side. These need medical assessment.
- For ordinary, lifestyle-related low energy, regular exercise has the best evidence, alongside sleep, food quality, daylight and managing alcohol and stress.
Two very different things: mitochondrial disease and everyday low energy
This distinction matters, so I want to be clear about it up front.
Primary mitochondrial disease is a group of inherited genetic conditions in which the mitochondria fail because of changes in the genes that build them. The Mito Foundation estimates that more than 4,600 Australians live with symptoms. Fatigue and muscle weakness are among the most common, but it can also affect the heart, brain, eyes, ears, kidneys and other organs, at any age. That variety is exactly why it is hard to diagnose. In one study of people with mitochondrial disease, about 62% reported excessive fatigue.
Everyday low energy is far more common. Here, the issue is not a genetic fault. It is the conditions your cells operate in: how much you move, sleep, eat, drink and stress. Researchers describe this as secondary mitochondrial dysfunction, where mitochondrial performance slips as a consequence of other factors. This is a looser, research-level idea, not a diagnosis you can get from a test at your GP.
Signs that get linked to poor mitochondrial function
Because mitochondria sit in nearly every cell, low energy can show up in several ways. Common reports include:
- Persistent fatigue that sleep does not fix
- Muscle weakness or heaviness, or tiring quickly with activity
- Slow recovery after exercise, or feeling worse for a day or two after effort
- Brain fog, with trouble concentrating or finding words
- Low exercise tolerance, such as being out of breath at modest effort
- Feeling the cold or getting sick often
Now the important caveat. Every item on that list also fits low iron, low B12, an underactive thyroid, sleep apnoea, depression, poorly controlled blood sugar, long COVID, medication side effects and plain overload. I am not aware of a validated, everyday test that can tell you your mitochondria are underperforming, and I would be cautious about commercial panels that claim to. The signs are real, but they point to many possible causes.
What to rule out first
If you have been flat for weeks, a visit to your GP is the right first step. Reasonable things to ask about include:
- A full blood count, ferritin and iron studies
- Vitamin B12 and folate, and vitamin D
- Thyroid function
- Blood sugar (fasting glucose or HbA1c)
- Kidney and liver function
- Screening for sleep apnoea if you snore, wake unrefreshed or feel sleepy by day
- A review of your medications, alcohol intake and mood
Our article on which health markers matter most explains how to make sense of these results.
When to ask about something more serious
See your GP promptly, and ask whether a specialist referral is appropriate, if you notice any of the following, particularly in combination:
- Unexplained, progressive muscle weakness or exercise intolerance
- Drooping eyelids or difficulty moving the eyes
- Hearing loss or vision loss
- Seizures, or recurrent unexplained headaches with vomiting
- Heart rhythm problems or heart failure at a young age
- Diabetes together with hearing loss
- A family history of similar problems, especially through the maternal line, because mitochondria and their DNA are passed down from the mother
The Mito Foundation in Australia offers information for patients and GPs, including a resource called "Maybe it's Mito". Their website at mito.org.au is a reliable place to start. Do not self-diagnose from a list, and do not start expensive supplements while waiting for a proper assessment.
What actually helps with everyday low energy
If your doctor has found nothing alarming, the foundations below are what the evidence supports most. They are simple, and they work together.
1. Move your muscles, regularly
This is the strongest lever we have. Research reviews conclude that endurance exercise improves mitochondrial function across the lifespan, and there is an active debate about how much of the decline we associate with ageing is really the result of becoming less active. You do not need extremes. Aim for regular walking, two short strength sessions a week, and a little bit of harder effort that gets your breathing up, adjusted to your health and with your doctor's guidance if you have a medical condition.
2. Eat enough protein and a wide range of whole foods
Your mitochondria need B vitamins, iron, magnesium, zinc, selenium, carnitine and coenzyme Q10 to work. A varied whole-food diet with quality protein, vegetables and healthy fats covers most of these. Be cautious about restrictive diets without testing and guidance. See our guide to mitochondrial health for the full picture.
3. Protect your sleep
Sleep is when much cellular maintenance happens. A regular bedtime and wake time, a dark, cool room and winding down from screens all help. If you suspect sleep apnoea, get it assessed.
4. Get daylight early
Morning outdoor light helps set your body clock, which influences sleep and energy through the day. We cover this in detail, including safe sun habits for Australia, in our article on morning light, mitochondria and energy.
5. Go easy on alcohol and look after stress
Alcohol and smoking add to oxidative stress, and long periods of stress and poor recovery wear you down. Small, regular recovery habits matter more than occasional big efforts.
6. Be sceptical about supplements and tests
Supplements such as CoQ10 or carnitine may help some people in specific situations, but they are not a substitute for the basics. If you are considering them, discuss them with a qualified professional, especially if you take medication. Fads like deuterium-depleted water are covered in our article on whether it is worth it.
A simple way to track what is happening
- Rate your energy out of 10 at midday and at 4pm for two weeks.
- Note your sleep times, movement, alcohol and caffeine.
- Change one thing at a time, such as a daily morning walk.
- Review the pattern after two to four weeks and bring it to your GP or nutritionist.
If your energy has not shifted after a month of steady basics, or you have any of the red flags above, it is time for a proper assessment.
Free download: the 2-week energy checklist
Want a ready-made way to track this? My free energy checklist includes a two-week tracker, shows you which of light, movement, food or sleep to work on first, and lists the red flags that mean it is time to see your GP.
Frequently asked questions
What are the signs of poor mitochondrial function?
Persistent fatigue, muscle weakness or heaviness, slow recovery after exercise and brain fog are commonly reported. These signs are not specific and have many other causes, so they need proper assessment.
Can I test my mitochondrial function?
I am not aware of a validated everyday test. Diagnosis of true mitochondrial disease involves specialist assessment, and routine blood tests are used mainly to rule out other causes of fatigue.
Is low energy always a mitochondrial problem?
No. Low iron, B12, thyroid problems, sleep apnoea, depression and medications are all common causes. These should be checked first.
How can I improve my mitochondria naturally?
Regular exercise has the strongest evidence, along with enough protein and nutrients, good sleep, morning daylight and limiting alcohol.
Do supplements like CoQ10 fix mitochondrial function?
They may help some people in specific circumstances, but they do not replace the basics. Speak with a qualified professional first.
When should I see a specialist?
If you have unexplained progressive weakness, eye muscle problems, hearing or vision loss, seizures, heart rhythm problems, or a family history that fits, ask your GP about referral.
Want help working out what is behind your energy?
If you are tired and not sure why, a conversation is often the quickest way to sort fact from hype. Book a free 15-minute clarity call and we can look at your history and decide what to check or change first. Online consultations are available.
About the author. Anthony Hartcher is a clinical nutritionist, lifestyle medicine specialist and science educator with about 30 years of professional experience. He holds a Bachelor of Engineering (Hons) in Chemical Engineering, a health science degree majoring in nutrition and dietetic medicine, and a degree in complementary medicine. He runs me&my wellness in Randwick, Sydney.
This article is general information and not a substitute for personal medical advice. It cannot diagnose any condition. Speak with your doctor if you have persistent or worrying symptoms.