Mitochondria turn food and oxygen into the energy your cells run on. Here's what they do, why they change with age, and what supports them.
Mitochondria are tiny structures inside almost every cell in your body that turn the food you eat and the oxygen you breathe into usable energy. Their output tends to decline with age and is shaped by sleep, movement, nutrition and stress. They're a genuinely interesting part of the energy story, but they're only one part, and persistent tiredness has many causes that are worth checking first.
What mitochondria actually do
Most people last heard "the powerhouse of the cell" in high school biology. It's a fair description. Mitochondria take energy from the food you eat and, using oxygen, convert it into a molecule called ATP, which is the form of energy your cells actually use.
Almost everything your body does runs on ATP, from contracting a muscle, sending a nerve signal, building proteins, running your immune system and maintaining tissues. Cells with high energy demands, like those in your heart, muscles and brain, contain large numbers of mitochondria. Others contain far fewer.
Where they came from
Mitochondria have an unusual backstory. Scientists widely accept that they began, a very long time ago, as free-living bacteria that were taken up by a larger cell. Instead of being digested, they stayed, and the partnership became the basis of complex life.
The evidence for this is still inside you. Mitochondria carry their own small set of DNA, separate from the DNA in the nucleus of your cells, and it's inherited almost entirely from your mother.
How they make energy
You don't need a biochemistry degree for the basics. Inside each mitochondrion is a folded inner membrane lined with a chain of protein machines. As energy from your food passes along this chain, it's used to pump particles across the membrane, building up a kind of pressure.
That pressure is released through a final protein that turns like a tiny turbine, assembling ATP as it spins. When the system is running well, it produces energy efficiently. It also creates some reactive by-products, often called free radicals, which your body's own defence systems normally keep in check.
Why mitochondrial function changes with age
Like most systems in the body, mitochondria change as the decades pass. Researchers consider declining mitochondrial function to be one of several features of ageing, alongside many other processes. A few things are thought to contribute.
- Wear from reactive by-products. Over time, these can damage mitochondrial membranes, proteins and DNA.
- Changes in mitochondrial DNA. Mitochondria copy their DNA often, and small errors can build up over a lifetime.
- Slower clean-up. Your body has a process for clearing out worn mitochondria and replacing them with new ones. This tends to slow with age.
- Less activity. Mitochondria respond to demand, so long stretches of inactivity mean fewer signals to maintain them.
It's worth keeping this in proportion. Ageing is complex, and mitochondria are one piece of it, not the single explanation for how you feel.
What supports healthy mitochondria
Mitochondria respond to how you live. They're not a set quantity you're stuck with, and the main influences are everyday ones.
Movement. Regular exercise is one of the clearest signals for your body to build more mitochondria and keep them working well. Both steady aerobic activity and harder efforts contribute, along with strength training for muscle.
Sleep. Good quality sleep supports the body's overnight maintenance. Adults generally need 7 to 9 hours, and quality matters as much as quantity. There's more in sleep quality versus sleep hours.
Nutrition. The energy machinery depends on adequate energy, protein and a range of vitamins and minerals, including iron and B vitamins. A varied diet built on whole foods covers most people's needs. If you think you might be low in something, ask a doctor to test rather than guessing.
Stress and recovery. Ongoing stress and poor recovery take a toll on the body's energy systems. Rest days, downtime and time away from constant pressure are part of the picture, not a luxury.
Mitochondria and feeling tired
It's tempting to see low energy as a mitochondria problem, and there's a lot of marketing that encourages that view. In practice, routine tests can't measure how well your mitochondria are working, and most people who feel persistently tired have more common, checkable causes.
Low iron, thyroid changes, blood sugar problems, sleep apnoea, low mood and simple sleep debt are all far more likely explanations. Rare inherited mitochondrial diseases do exist, but they're diagnosed and managed by specialists and usually involve a distinct pattern of symptoms. For a practical starting point, see what blood tests check for tiredness.
When to talk to a doctor
See a doctor if you've felt tired most days for more than a few weeks, if you're finding exercise much harder than it used to be, or if you're recovering slowly from activity or illness. Get checked promptly if tiredness comes with muscle weakness, unexplained weight loss, fevers, night sweats or breathlessness. If you have chest pain, trouble breathing or feel faint, call 000.
How UHD BioHealth can help
UHD BioHealth is a doctor-led telehealth service available across Australia. You start with a detailed online questionnaire, and an AHPRA-registered doctor reviews it within 24 hours. Where it's useful, your doctor will recommend bloodwork you can do locally, then you receive a written personalised plan with every cost listed before you pay anything, checked by a second, independent doctor, with follow-up care along the way. See what a doctor looks at for low energy.
Common questions
Why do mitochondria have their own DNA?
Mitochondria are thought to have evolved from free-living bacteria that were taken up by early complex cells, and their separate DNA is a remnant of that history. It's passed down almost entirely through the mother, which is why it's been so useful for tracing human ancestry.
How does exercise affect mitochondria?
Regular exercise creates an energy demand that signals your cells to build more mitochondria and keep existing ones in good working order. Both aerobic exercise and higher-intensity efforts play a part, and the effect builds with consistency over time.
Can a blood test check my mitochondria?
Not in a routine way. Standard blood tests don't measure how well your mitochondria are working. They can, however, check common causes of low energy such as iron, thyroid function and blood sugar, which is usually the most useful place to start.
Running on empty by 3pm
An in-depth health questionnaire covering your history, symptoms, medications and lifestyle, read by an AHPRA-registered doctor within 24 hours. Bloodwork where it's needed, and a written plan before you pay anything.
Not ready for that yet? Get our free guide, What a doctor checks when you're always tired.
General health information only, not medical advice. Complete our questionnaire and a doctor will assess whether a consult is right for you. Individual needs and outcomes vary. In an emergency, call 000.
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