What Are Mitochondria? Their Function, Explained

Mitochondria are tiny structures inside your cells whose main function is to turn the energy in food into ATP (adenosine triphosphate), the molecule cells spend to do work¹. They do it by combining oxygen with fuel from sugars and fats². They also make heat, handle calcium and decide when a damaged cell should die^{3, 4, 5}.

Most cells hold hundreds to thousands of them, and each carries its own small set of DNA⁶. For the supplements studied for energy and mitochondrial health, see our energy and mitochondrial function hub. This guide covers the biology, and what the human evidence says actually changes how mitochondria work.

The main function of mitochondria is energy production: they are responsible for most ATP synthesis in cells that use oxygen⁷. That is why they are nicknamed the powerhouse of the cell. But they also make building blocks, send signals and take part in cell clean-up and cell death⁵. Their main jobs:

• Energy (ATP) production. They break down fuel and use oxygen to generate ATP through cellular respiration⁷.
• Heat generation. In brown fat, mitochondria carry uncoupling protein 1 (UCP1), which short-circuits energy production so the energy is released as heat instead of ATP³. This is thermogenesis. A scan study of 1,972 adults found active brown fat in 7.5% of women and 3.1% of men⁸.
• Calcium handling. Mitochondria take up and release calcium, and calcium in turn tunes their energy output and their production of reactive oxygen species⁴.
• Deciding when a cell dies. Cytochrome c normally ferries electrons inside mitochondria. When it is released into the rest of the cell, it activates the enzymes (caspases) that take the cell apart in a controlled way (apoptosis)⁹.
• Making molecules. Mitochondria produce many biosynthetic building blocks⁵. One example: the heme in your red blood cells' hemoglobin is made in mitochondria¹⁰.

Mitochondria pull electrons out of food fuel, pass them down a chain of proteins, and use that flow to drive ATP synthase, the enzyme that makes ATP⁷. The process, called oxidative phosphorylation, runs in these steps:

1. Fuel enters. Products of sugar and fat breakdown enter the matrix, the inner space, where the citric acid (Krebs) cycle and fat-burning enzymes strip electrons from them⁷.
2. Electron carriers load up. Those electrons are carried by NAD, which your body makes from niacin (vitamin B3), and by FAD, made from riboflavin (vitamin B2)^{11, 12}.
3. The electron transport chain. Electrons flow through complexes I to IV in the inner membrane and end on oxygen. Complexes I, III and IV pump protons out of the matrix as they go⁷.
4. ATP synthase. Protons flow back in through ATP synthase, and that flow powers ATP production⁷.

This is why you need oxygen: it is the last stop for the electrons. Mitochondrial DNA codes for 13 proteins in this machinery⁶. The rest of the parts are made from nuclear genes and imported into the mitochondrion⁷.

A mitochondrion is a compartment wrapped in two membranes, which is unusual for a structure inside a cell¹. In living cells they also link into a branching, changing network rather than sitting apart⁵. The parts, from outside in:

• Outer membrane: fairly leaky, letting small molecules through⁷.
• Intermembrane space: the gap between the two membranes, where cytochrome c sits^{7, 9}.
• Inner membrane: folded into ridges called cristae, it holds the four electron transport complexes, ATP synthase and the transporters that move fuel in⁷.
• Matrix: the gel-like core holding the citric acid cycle enzymes, fat-burning enzymes and the mitochondrial DNA⁷.

The human mitochondrial genome was fully sequenced in 1981 and is 16,569 base pairs long¹³. It holds 37 genes, all needed for normal mitochondrial function⁶. Your nuclear DNA, by comparison, holds the instructions for every other mitochondrial protein⁷.

Cells with the highest energy demands have the most mitochondria: heart muscle, skeletal muscle, liver, kidney and brain¹. A typical cell holds hundreds to thousands of them⁶.

• Heart muscle cells: 30-40% of their volume is mitochondria, which supply up to 90% of the beating heart's ATP⁴. The heart turns over about 15 times its own weight in ATP every day¹⁴.
• Muscle and nerve cells: their high energy needs are why muscle weakness and neurological problems are common features of mitochondrial disease¹⁵.
• Mature red blood cells: none at all. They clear out their mitochondria as they mature and make ATP by glycolysis, a pathway that needs no mitochondria¹⁰.

Do animal and plant cells both have mitochondria?

Yes. Mitochondria are in almost all of the cells in your body¹⁵. Plant cells have them too, alongside chloroplasts. Both organelles can make ATP: chloroplasts from light, mitochondria from fuel and oxygen¹⁶. When a leaf is fixing carbon dioxide at full speed, its mitochondria supply most of the ATP for the rest of the cell¹⁶.

Mitochondria descend from bacteria. All of them trace back to an alphaproteobacterium that was taken in by an ancestral host cell, related to the Asgard archaea, and over time became a permanent part of it¹⁷. Along the way it lost most of its genes, many of them moved to the host's nucleus¹⁷.

In your own body, mitochondria come from your mother. Sperm do carry mitochondria into the egg, but a 2023 study found that human sperm mitochondria lack intact mitochondrial DNA, which explains why only the mother's is passed on^{18, 1}. From there, existing mitochondria grow, fuse and divide as a network to make more⁵.

This inheritance pattern now has a medical workaround. In a 2025 UK program, mitochondrial donation by pronuclear transfer led to 8 live births to women carrying harmful mitochondrial DNA variants¹⁹. In 6 of the 8 babies, levels of the mother's variant were 95-100% lower than in the original fertilized egg¹⁹. In the other 2 they were 77-88% lower, and blood levels across the 8 babies ranged from undetectable to 16%¹⁹, so the procedure reduces the variant rather than always removing it.

Two groups of disease involve mitochondria: inherited mitochondrial diseases, where the energy machinery itself is faulty, and common diseases that damage mitochondria along the way^{20, 15}.

Inherited (primary) mitochondrial disease

Mitochondrial diseases are the most common group of inherited metabolic disorders²⁰. A study of adults in North East England put the minimum prevalence at about 1 in 4,300, counting faults in both mitochondrial and nuclear DNA²¹. Symptoms are worst in tissues with high energy needs¹⁵:

• Muscles: fatigue, weakness and exercise intolerance¹⁵.
• Brain and nerves: seizures, migraine, balance problems and stroke-like episodes¹⁵.
• Eyes and ears: drooping eyelids, vision loss and hearing loss¹⁵.
• Other organs: heart rhythm problems, diabetes and kidney problems¹⁵.

Named syndromes include MELAS, Leigh syndrome, MERRF and Leber hereditary optic neuropathy. One single DNA change, A3243G, causes more than 80% of MELAS cases⁶.

Dysfunctional mitochondria in common diseases and aging

Type 1 diabetes, cancer, multiple sclerosis and Alzheimer's disease can cause secondary mitochondrial damage, which is not inherited¹⁵. Damage to mitochondrial DNA also builds up with age and has been linked to heart disease, Alzheimer's and Parkinson's disease⁶. In 146 healthy adults aged 18 to 89, muscle mitochondrial DNA and ATP production both fell with age, and lower ATP production tracked with lower aerobic fitness and poorer glucose tolerance²².

There is no simple home or blood test that tells you whether your mitochondria are healthy. Doctors diagnose mitochondrial disease with a combination of tests¹⁵:

• History and exams: family history, strength and endurance tests, reflexes, vision and hearing¹⁵.
• Lab tests: lactic acid in blood and urine, plus checks for diabetes and liver and kidney problems¹⁵.
• Heart and brain tests: an EKG, and MRI or CT scans of the brain¹⁵.
• Genetic testing: a positive result confirms the diagnosis, but a negative one does not rule it out¹⁵.
• Muscle biopsy: stained muscle can show ragged red fibers, a sign of abnormal mitochondria¹⁵.

The Mitochondrial Medicine Society's consensus statement sets out how specialists should use these tests²³. In research, aerobic fitness goes along with muscle mitochondrial ATP production²², but it also depends on the heart and lungs, so it is a rough clue rather than a test. Ordinary tiredness has many causes, though. Our pages on chronic fatigue and exercise intolerance cover the common ones.

Regular endurance exercise is the best-proven way to increase your mitochondria. The process is called mitochondrial biogenesis. A 2025 meta-analysis of randomized trials in healthy people found that endurance exercise raised PGC-1α, the most consistently reported marker of biogenesis, with a large effect (Hedges' g 1.17), though results varied widely between studies²⁴. Interval and continuous training worked about equally well²⁴.

• Volume builds more mitochondria. A review of human training studies concluded that total training volume may be the key factor in gains in mitochondrial content²⁵.
• Intensity improves how well they work. The same review found relative intensity was an important factor in respiratory function²⁵.
• Gains fade fast. In 10 healthy men, 20 days of twice-daily interval training raised mitochondrial respiration and citrate synthase activity by about 40-50%. After 2 weeks of reduced training, most measures were back to baseline²⁶.

The practical reading: consistent weekly training volume matters more than any single hard session.

No supplement has been shown to repair mitochondria. In people with inherited mitochondrial disease, a Cochrane review of 12 randomized trials found no clear evidence for any treatment, including vitamins and supplements²⁷:

• CoQ10: high doses brought no clinically meaningful improvement in 30 participants²⁷. Its use outside inherited disease is graded on our CoQ10 for ATP production page.
• Creatine: 1 of 3 small trials (38 people in total) found better muscle strength; the other 2 found no benefit²⁷.
• CoQ10, creatine and alpha-lipoic acid together: improved lab markers and one ankle-strength measure in 16 people, but brought no overall clinical improvement²⁷.

In healthy older adults, a 2022 systematic review found only 6 randomized trials with 201 participants that measured mitochondrial changes, too few to draw firm conclusions²⁸. The two most studied newer compounds:

• Urolithin A: in 66 adults aged 65 to 90, 1,000 mg a day for 4 months improved muscle endurance, but not walking distance or maximal muscle ATP production, the main outcomes²⁹. In middle-aged adults it raised muscle strength by about 12% but missed its main outcome, peak power³⁰. Our page on urolithin A for mitochondrial biogenesis grades these trials.
• Nicotinamide riboside, a form of vitamin B3: 1 g a day for 21 days raised NAD-related molecules in the muscle of 12 older men without changing mitochondrial energy output³¹. In 40 men with obesity, 1,000 mg twice daily for 12 weeks did not change muscle mitochondrial respiration, content or shape³².

Supplements in this guide

• CoQ10
• Creatine Monohydrate
• Urolithin A
• Alpha Lipoic Acid (ALA)
• Vitamin B3
• Vitamin B2

No food has been shown in human trials to repair mitochondria. What food does supply is the nutrients, mainly B vitamins, the energy machinery runs on^{12, 11}:

• Riboflavin (vitamin B2): forms FAD and FMN, coenzymes with major roles in energy production. Adults need 1.1-1.3 mg a day; eggs, organ meats, lean meats and milk are rich sources¹².
• Niacin (vitamin B3): becomes NAD, which more than 400 enzymes need and which moves the energy in carbohydrates, fats and protein into ATP. Poultry, beef and fish give about 5-10 mg per serving; nuts, legumes and grains about 2-5 mg¹¹.

Both are water-soluble B vitamins; our guide to fat-soluble vs water-soluble vitamins explains what that means for daily intake.

As for foods that are bad for mitochondria: we found no human trial that measured mitochondrial function after eating a specific food. Lists of foods that damage mitochondria are not based on that kind of evidence.

People with a diagnosed mitochondrial disease should exercise, but carefully. Moderate exercise helps maintain strength, while overdoing it can break down muscle and leak myoglobin into the urine, which strains the kidneys¹⁵. Dark, red or cola-colored urine is a sign of this muscle breakdown (rhabdomyolysis); contact a doctor if it happens, because prompt treatment lowers the risk of lasting kidney damage³³. Exercise programs should be physician-led¹⁵.

• People with a mitochondrial diagnosis: there are no specific treatments that fix the underlying defect; vitamins and supplements are used to manage symptoms, under a specialist¹⁵.
• People with a mitochondrial diagnosis, or a family history of one: tell every prescriber. The seizure drug valproate (valproic acid) carries an FDA boxed warning: it can cause fatal liver failure in people with mitochondrial disease caused by POLG gene changes, and must not be used in them or in children under 2 suspected of having a mitochondrial disorder³⁴. Aminoglycoside antibiotics, such as gentamicin and tobramycin, can cause permanent hearing loss in people with certain mitochondrial DNA variants, particularly m.1555A>G, even when blood levels of the drug stay in the recommended range³⁵.
• Women carrying a mitochondrial DNA variant who plan a pregnancy: these variants pass through the mother, and a doctor or genetic counselor can explain the risks and options, including mitochondrial donation^{15, 20, 19}.
• Anyone with new muscle weakness, drooping eyelids, vision or hearing loss plus fatigue: this mix is worth a doctor's assessment rather than a supplement trial¹⁵.

For a healthy adult who wants mitochondria that work well, the evidence points to one main lever: regular endurance exercise, kept up week after week^{24, 26}. A simple decision rule:

• If you want more mitochondria: build weekly aerobic volume first, then add intervals for respiratory function²⁵.
• If you eat a varied diet with meat, eggs, dairy, legumes or grains: those foods are your main sources of riboflavin and niacin^{12, 11}.
• If you are thinking about a mitochondria supplement: expect small or no effects; the best trials of urolithin A and nicotinamide riboside missed their main outcomes^{29, 32}.
• If you have unexplained muscle weakness and exercise intolerance: see a doctor; mitochondrial disease is diagnosed with lab, genetic and muscle tests, not symptoms alone¹⁵.

We searched PubMed, the Cochrane Library, NIH sources (NHGRI, MedlinePlus, NINDS, the Office of Dietary Supplements) and FDA drug labels on 14 October 2026. We read 28 journal records, 7 NIH pages and 2 FDA labels, and cited 26, 7 and 2 of them. We gave priority to systematic reviews, randomized trials in humans, NIH reference pages and FDA safety warnings, and used biology reviews for how mitochondria work. The trials of supplements for mitochondrial health are small and short, so the evidence cannot tell us whether any supplement changes long-term health through mitochondria.

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27. Pfeffer G, et al. Treatment for mitochondrial disorders. Cochrane Database Syst Rev. 2012;2012(4):CD004426. doi:10.1002/14651858.CD004426.pub3
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29. Liu S, et al. Effect of Urolithin A Supplementation on Muscle Endurance and Mitochondrial Health in Older Adults: A Randomized Clinical Trial. JAMA Netw Open. 2022;5(1):e2144279. doi:10.1001/jamanetworkopen.2021.44279 Our study summary.
30. Singh A, et al. Urolithin A improves muscle strength, exercise performance, and biomarkers of mitochondrial health in a randomized trial in middle-aged adults. Cell Rep Med. 2022;3(5):100633. doi:10.1016/j.xcrm.2022.100633 Our study summary.
31. Elhassan YS, et al. Nicotinamide Riboside Augments the Aged Human Skeletal Muscle NAD+ Metabolome and Induces Transcriptomic and Anti-inflammatory Signatures. Cell Rep. 2019;28(7):1717-1728.e6. doi:10.1016/j.celrep.2019.07.043 Our study summary.
32. Dollerup OL, et al. Nicotinamide riboside does not alter mitochondrial respiration, content or morphology in skeletal muscle from obese and insulin-resistant men. J Physiol. 2020;598(4):731-754. doi:10.1113/JP278752 Our study summary.
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35. U.S. Food and Drug Administration. Tobramycin for Injection prescribing information (2023), Risk of Ototoxicity Due to Mitochondrial DNA Variants. https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/050789s017lbl.pdf