The heart has more mitochondria because it never stops working. Heart muscle cells contract around the clock, and they get more than 95% of their ATP, the cell's energy molecule, from mitochondria. To keep up with that demand, mitochondria fill roughly a quarter to a third of each heart muscle cell, far more than in most other cells.
Key Takeaways
- Heart muscle cells (cardiomyocytes) get more than 95% of their ATP from mitochondria, and they store only a few seconds' worth of ready energy.
- Mitochondria make up about 23% of human heart muscle tissue by volume in biopsy studies; reviews describe figures of 30% or more for adult heart cells.
- A human heart turns over an amount of ATP equal to 15 to 20 times its own weight every day.
- Normal mitochondrial energy metabolism depends on nutrients such as riboflavin, niacin, magnesium and iron, plus coenzyme Q10, which the body makes itself.
- In human studies, endurance training increases mitochondrial content in muscle, while mitochondrial ATP production in muscle tends to fall with age.
Evidence grade: Strong. The heart's reliance on mitochondria is established by decades of tissue measurements in human and animal hearts, and the nutrient roles described here come from NIH Office of Dietary Supplements fact sheets.
Why Heart Cells Need So Much Energy
The heart is a muscle that cannot rest. Every beat requires heart muscle cells to contract and then relax, and both steps use ATP. A 2013 review in Circulation Research notes that a heart cell's stored high-energy phosphate is only enough to sustain the heartbeat for a few seconds. That means ATP production has to stay tightly matched to the work the heart is doing, beat after beat [7].
The same review puts the scale in perspective: over one day, a human heart turns over an amount of ATP equal to 15 to 20 times its own weight [7]. No storage system could hold that much. The heart has to make its energy continuously, and mitochondria are where most of it is made.
To meet this constant demand, the heart burns several fuels. A 2010 review in Physiological Reviews explains that the heart's energy needs are met primarily by breaking down long-chain fatty acids, with glucose, lactate, ketones and amino acids also used depending on workload, hormones and oxygen supply [8]. All of these fuels feed into mitochondria.
How Much of a Heart Cell Is Mitochondria?
Heart muscle is one of the most mitochondria-dense tissues in the body. In a classic 1985 study that measured biopsied human heart tissue under the electron microscope, mitochondria made up 23% of the tissue volume, with contractile fibers making up 59% [9]. Reviews of adult heart cells often cite figures of at least 30% of cell volume [10]. The figure varies with species, cell type and measuring method.
The same 1985 study found that smaller animals with faster heart rates had more mitochondria, up to 32% in mice, and that mitochondrial volume tracked with heart rate and oxygen consumption [9]. In other words, the more work a heart does, the more mitochondria it carries.
For a closer look at the numbers, including how researchers count mitochondria, see our article on the number of mitochondria in heart cells.
How Mitochondria Make ATP
Most cells contain hundreds to thousands of mitochondria [6]. Inside each one, a process called oxidative phosphorylation uses oxygen and the breakdown products of food to make ATP [6]. Electrons pass along a chain of protein complexes in the inner mitochondrial membrane, and the energy released drives ATP production.
Mitochondria also carry their own small set of genes. Mitochondrial DNA contains 37 genes, and 13 of them provide instructions for enzymes used in oxidative phosphorylation [6]. Most of the other proteins mitochondria need are made from genes in the cell nucleus.
In heart cells, mitochondria do more than make ATP. They help regulate calcium inside the cell, take part in cell signaling, and help control whether damaged cells are removed [7]. Researchers also study how changes in heart mitochondria relate to cardiovascular conditions [10]. That is clinical territory, and anyone with symptoms or a family history should talk to a doctor.
Nutrients Involved in Mitochondrial Energy Metabolism
Mitochondria rely on vitamins, minerals and other compounds to turn food into ATP. A varied diet supplies most of them. Here are the ones most directly tied to the process.
| Nutrient | Role in energy metabolism | Adult reference point |
|---|---|---|
| Riboflavin (vitamin B2) | Forms FMN and FAD, coenzymes with major roles in energy production [2] | No upper limit set; no adverse effects reported from high intakes [2] |
| Niacin (vitamin B3) | Converted to NAD, which more than 400 enzymes require; NAD and NADP carry electrons in metabolic reactions [3] | Nicotinic acid in large supplemental amounts can cause skin flushing [3] |
| Magnesium | Required for energy production, oxidative phosphorylation and glycolysis [1] | RDA 310 to 420 mg from all sources; supplement upper limit 350 mg a day [1] |
| Iron | Part of hemoglobin and myoglobin, which deliver and hold the oxygen mitochondria use; supports muscle metabolism [4] | Upper limit 45 mg a day [4] |
| Coenzyme Q10 | Made by the body; naturally present, with the highest levels in the heart, liver, kidneys and pancreas [5] | No established requirement; sold as a dietary supplement [5] |
Coenzyme Q10
Coenzyme Q10 (CoQ10) is made by your own cells, and the heart is one of the places it is most concentrated [5]. Because CoQ10 has important functions in the body, researchers have studied whether supplements offer benefits. The National Center for Complementary and Integrative Health (NCCIH) reports that research on CoQ10 supplements for heart-related outcomes is so far inconclusive, so it is best viewed as part of a general wellness routine rather than a fix for any specific concern [5].
For adults who choose a supplement, OPA CoQ10 Ubiquinone provides 200 mg of coenzyme Q10 as ubiquinone in one capsule a day. It is part of the OPA Core Series, formulated for cellular energy and antioxidant support, and each bottle holds a 30-day supply.
B vitamins, magnesium and iron
Riboflavin and niacin supply the coenzymes (FAD, FMN and NAD) that shuttle electrons through energy-producing reactions [2][3]. Magnesium is needed for oxidative phosphorylation itself [1]. Iron supports the oxygen supply that mitochondria depend on [4]. For more on iron and energy, read the role of iron in energy levels.
What Affects Mitochondrial Function
Exercise training
Exercise is the best-studied way to change mitochondria in people. A 2018 review in Sports Medicine found that endurance training increases mitochondrial content and function in human muscle. Training volume appeared to matter most for how many mitochondria muscle builds, while exercise intensity mattered most for how well they work [11]. Most of this human evidence comes from skeletal muscle biopsies, since healthy people rarely give heart tissue samples. For practical options, see the best exercise to increase mitochondria.
Aging
Mitochondrial output tends to fall with age. A 2005 study of 146 healthy adults aged 18 to 89 found that mitochondrial DNA, and the rate at which muscle mitochondria made ATP, declined with advancing age. Mitochondrial ATP production was closely linked with aerobic fitness [12]. Staying active is one of the few factors shown to influence these changes. For a broader overview, see our guide to mitochondrial health.
Safety and Interactions
Food is the safest way to get most of the nutrients above. If you use supplements, keep these points in mind:
- CoQ10: No serious side effects have been reported. Mild insomnia or digestive upset can occur. Talk to your doctor or pharmacist if you take warfarin or insulin, as CoQ10 may interact with them, or if you are receiving cancer treatment [5]. See what medications should not be taken with CoQ10.
- Magnesium: Keep supplemental magnesium at or below 350 mg a day unless your doctor advises otherwise. Too much can cause diarrhea, nausea and cramping. Talk to your doctor or pharmacist if you take bisphosphonates, tetracycline or quinolone antibiotics, diuretics or proton pump inhibitors [1].
- Iron: The upper limit is 45 mg a day, and higher doses can cause nausea and constipation. Talk to your doctor or pharmacist if you take levodopa, levothyroxine or proton pump inhibitors [4]. Do not take iron unless you know you need it.
- Niacin: Nicotinic acid in high supplemental doses can cause flushing [3].
If you have a heart condition, are pregnant or breastfeeding, or take prescription medicines, talk to your healthcare provider before starting a supplement or a new exercise program.
Frequently Asked Questions
Why does the heart have more mitochondria than other organs?
Because it works nonstop. Heart muscle cells contract with every beat and hold only a few seconds of stored energy, so they must make ATP continuously. Mitochondria supply more than 95% of that ATP, so heart cells carry far more of them than most other cells.
What percentage of a heart cell is mitochondria?
About 23% of human heart muscle tissue was mitochondria in a classic biopsy study, and reviews often cite 30% or more for adult heart cells. The exact number depends on the method. Our article on the number of mitochondria in heart cells covers the figures in detail.
Does the heart use mitochondria for all of its energy?
Almost all of it. Mitochondria produce more than 95% of the ATP the heart uses, mainly by burning fatty acids, with glucose, lactate, ketones and amino acids used as well. The small remainder comes from processes outside the mitochondria.
Do heart mitochondria do anything besides make energy?
Yes. They help manage calcium inside heart cells, take part in cell signaling, and help decide whether damaged cells are cleared away. These roles are part of why researchers study heart mitochondria so closely.
Can exercise increase mitochondria?
Yes, in muscle. Human studies show that endurance training increases mitochondrial content and function in skeletal muscle. Training volume seems to drive the amount, and intensity seems to drive how well they work. Talk to your doctor before starting a new program if you have a heart condition.
Which nutrients support normal mitochondrial energy metabolism?
Riboflavin and niacin supply coenzymes used in energy production, magnesium is required for oxidative phosphorylation, and iron supports oxygen delivery to muscle. The body also makes its own CoQ10. A balanced diet covers most of these needs for most people.
Sources
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals.
- NIH Office of Dietary Supplements. Riboflavin: Fact Sheet for Health Professionals.
- NIH Office of Dietary Supplements. Niacin: Fact Sheet for Health Professionals.
- NIH Office of Dietary Supplements. Iron: Fact Sheet for Health Professionals.
- National Center for Complementary and Integrative Health. Coenzyme Q10.
- MedlinePlus Genetics. Mitochondrial DNA. National Library of Medicine.
- Kolwicz SC Jr, Purohit S, Tian R. Cardiac metabolism and its interactions with contraction, growth, and survival of cardiomyocytes. Circ Res. 2013.
- Lopaschuk GD, Ussher JR, Folmes CD, Jaswal JS, Stanley WC. Myocardial fatty acid metabolism in health and disease. Physiol Rev. 2010.
- Schaper J, Meiser E, Stämmler G. Ultrastructural morphometric analysis of myocardium from dogs, rats, hamsters, mice, and from human hearts. Circ Res. 1985.
- Piquereau J, Caffin F, Novotova M, et al. Mitochondrial dynamics in the adult cardiomyocytes: which roles for a highly specialized cell? Front Physiol. 2013.
- Granata C, Jamnick NA, Bishop DJ. Training-induced changes in mitochondrial content and respiratory function in human skeletal muscle. Sports Med. 2018.
- Short KR, Bigelow ML, Kahl J, et al. Decline in skeletal muscle mitochondrial function with aging in humans. Proc Natl Acad Sci U S A. 2005.
Disclosure: OPA Nutrition sells supplements, including products mentioned in this article. This content is for education only and is not medical advice. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your healthcare provider before using any supplement, especially if you take medication or have a medical condition.
Written and reviewed by Michael Gonzales, Founder, OPA Nutrition · Last reviewed: · How OPA researches and writes
