Liver functions

Calling the liver the body's chemical hub is not an exaggeration. Sitting just under the ribcage, it coordinates a broad set of processes that hold the body in balance: it runs metabolism by processing the nutrients in food, regulates the supply of energy, backs up the immune system, detoxifies harmful substances, banks essential vitamins and minerals, and helps keep hormone levels in check.¹ ² ³

What is striking about the liver is not only how many jobs it holds — more than 500 distinct functions — but how tightly those jobs interlock. It partners with the digestive system to process what we eat, with the endocrine system to regulate metabolism, and with the immune system to fend off pathogens.¹ ² Every compound entering or leaving the body passes through this hub, where liver cells transform it, store it, or route it to wherever it is needed.

So when the liver falters, the consequences do not stay local. Digestion, metabolism, immunity and more are all disturbed. That interdependence is exactly why the liver is not simply one organ among many but a keystone of human physiology, sustaining life through constant and complex work that goes largely unnoticed.³

Key functions of the liver³

1. Blood cleansing

2. Metabolising nutrients and compounds

3. Producing bile

4. Storing essential nutrients

Blood cleansing

Clearing waste products, toxins and pathogens, while holding a reserve supply of blood.

Blood cleansing and the removal of drugs, hormones and other substances

Most of the blood arriving at the liver has come straight from the gut. It is loaded with nutrients from digestion — but it may carry toxins and other harmful substances along with them.

The liver's defence is a population of specialised immune cells, the Kupffer cells: large, highly efficient filters that trap and destroy very nearly all bacteria and unwanted particles in the blood passing through. Alongside this, the liver neutralises harmful compounds by binding them to other molecules, which both blunts their effects and makes them easier to excrete.

Drug detoxification and clearance is a major part of this work, with many drugs excreted into bile. The liver also processes hormones produced by the endocrine glands, including thyroid hormones and most steroid hormones — estrogen, cortisol and aldosterone among them. If the liver is damaged, those hormones can build up in the blood and drive certain hormonal systems into overactivity.

Metabolising nutrients and compounds

Handling carbohydrates, proteins, fats, hormones, and foreign chemicals such as medications.

a. Carbohydrate metabolism

How the body handles carbohydrates is largely determined in the liver. Its principal roles here are:

1. Storing glycogen — the storage form of glucose, the body's main energy source

2. Manufacturing new glucose through gluconeogenesis

3. Producing a range of compounds from the breakdown products of carbohydrates

Stable blood sugar depends on this. After a meal, when blood sugar is high, the liver banks the surplus as glycogen; later, when blood sugar falls, it releases glucose back into circulation. Gluconeogenesis contributes to the same stability from the other direction, converting amino acids and glycerol drawn from fats into glucose when levels run low.

Where the liver is not working properly, blood sugar following a carbohydrate-heavy meal can climb to two or three times the normal level.

b. Fat metabolism

Most cells can process fats, but several decisive steps happen mainly in the liver:

1. Breaking fatty acids down to produce energy for the body

2. Producing cholesterol, phospholipids and most lipoproteins in large quantities — all compounds essential to the structure of our cells

3. Converting proteins and carbohydrates into fat for storage

Around 80% of the cholesterol the liver makes is converted into bile salts and released in bile to assist fat digestion. The remainder travels through the bloodstream packaged inside lipoproteins, supplying cells throughout the body.

The liver also makes phospholipids, which — like cholesterol — are indispensable for building cell membranes, internal cell structures and a variety of essential molecules. Most of the fat the body produces from carbohydrates and proteins is made here too. Once assembled, those fats are packed into lipoproteins and dispatched to adipose (fat) tissue for storage.

c. Protein metabolism

The liver's contribution to protein metabolism is so essential that life can continue only a few days without it. Its main functions are:

1. Processing amino acids — the building blocks of proteins — so they can be used for energy, while ensuring the harmful byproducts of that processing are safely removed

2. Producing the plasma proteins that circulate in the blood, such as clotting factors and albumin

Producing bile

Essential for digesting and absorbing fats.

Bile production and its role in digestion

The liver produces between 600 and 1000 ml of bile a day, serving two purposes:

1. Aiding fat digestion and absorption. Bile contains no fat-digesting enzymes itself; its bile acids work in two other ways:

   • Emulsifying fats — breaking large fat droplets into tiny particles so that pancreatic lipase, the digestive enzyme, can work on them effectively.

   • Assisting absorption — helping the intestinal lining take up the end products of fat digestion.

2. Removing waste products. Bile carries substances out of the blood, notably bilirubin — a byproduct of red blood cell breakdown — and surplus cholesterol.

Liver cells produce bile continuously, but it is normally held in the gallbladder until digestion calls for it in the duodenum. Bile is mostly water; its principal solutes are bile salts (about half of the total solids), bilirubin, cholesterol and the usual plasma electrolytes.

Storing essential nutrients

Vitamins and iron, held for future use.

The liver's storage capacity is considerable, particularly for vitamin A, vitamin D and vitamin B12. These reserves shield the body from deficiency through periods of low intake — though the reserves themselves depend on diet, and if intake stays low the tank never really fills. Deficiencies generally trace to one of three causes: too little in the diet, poor absorption (digestive problems, for instance), or increased demand — stress, illness, inflammation, certain medications, alcohol or smoking.⁴

1. Iron, stored as ferritin. Setting aside the iron carried in haemoglobin, most of the body's iron is held in the liver as ferritin. Liver cells contain a protein called apoferritin that binds iron when blood levels are high, forming ferritin and allowing the surplus to be stored. When blood iron drops, ferritin gives that iron back to circulation. The apoferritin–ferritin system therefore acts as both reserve and regulator, keeping blood iron levels stable.

2. Vitamin A: enough is stored to prevent deficiency for as long as 10 months.

3. Vitamin D: reserves last 3 to 4 months.

4. Vitamin B12: stores are large enough to last at least a year, and possibly several.

When the liver falters

The functions above assume a liver working as intended. When metabolising nutrients falls behind, fat starts to accumulate in liver cells instead of being processed and cleared — non-alcoholic fatty liver disease (NAFLD), typically downstream of being overweight, elevated blood sugar, dyslipidemia or high blood pressure. Once inflammation joins that fat buildup, the disease can progress from simple steatosis toward cirrhosis.⁵ NAFLD is already the most common liver disease in the world, reaching an estimated one in three American adults, and projections put more than half of the adult population on course to have it by 2040.⁵ ⁶

Risk factors, per the American Gastroenterological Association, include:⁵

Medical conditions

• Obesity

• Metabolic syndrome

• Insulin resistance

• Type 2 diabetes mellitus

• Dyslipidemia

• Hypertension

• PCOS

• Thyroid disease

Nutrition and behaviour

• Alcohol

• Ultra-processed foods

• Fructose

• Sedentarism

• Choline deficiency

Left unchecked, this reaches into the four chronic diseases responsible for most deaths worldwide.⁷ Cardiovascular disease is the leading cause of death in the United States,⁸ and it traces back in large part to fatty liver disease and liver dysfunction.⁵ ⁹ When calorie intake — sugar in particular — outruns what the liver can process, the organ stores the surplus as fat, loses its sensitivity to insulin, and releases excess glucose and fatty acids into the bloodstream; sustained over years, this raises the risk of both heart disease and type 2 diabetes.⁷ ⁹ The same dysfunction is linked to higher rates of colorectal and other cancers, most likely through a combination of insulin-driven cell proliferation and chronic inflammation supplying tumour-promoting signals, and to a heightened risk of Alzheimer's disease, where insulin resistance and inflammation together weaken the blood–brain barrier and interfere with neuronal insulin signalling.⁷

Conclusion

The liver, in short, works hard — carrying out countless vital functions every day. The encouraging part is its extraordinary capacity for self-repair. When a substantial portion of liver tissue is lost, whether through partial surgical removal (partial hepatectomy) or acute injury, the organ can regenerate. After a partial hepatectomy removing as much as 70% of the liver, the remaining lobes enlarge rapidly through cell growth and division, and the process continues until the original mass is restored — allowing the liver to resume its work in metabolism, detoxification and nutrient storage.³

References

Cited by the original article:

1. Kalra A, Yetiskul E, Wehrle CJ, et al. Physiology, Liver. [Updated 2023 May 1]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. https://www.ncbi.nlm.nih.gov/books/NBK535438/

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3. Hall, J. E. (2021). Guyton and Hall textbook of medical physiology (14th ed.). Elsevier.

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6. Le MH, Yeo YH, Zou B, et al. Forecasted 2040 global prevalence of nonalcoholic fatty liver disease using hierarchical bayesian approach. Clin Mol Hepatol. 2022;28(4):841-850. doi:10.3350/cmh.2022.0239

7. Attia P. Outlive: The Science and Art of Longevity. New York, NY: Harmony/Rodale; 2023.

8. Centers for Disease Control and Prevention. (2025). CDC WONDER Online Database: Data Request D176.

9. Nakashima M, Nakamura K, Nishihara T, et al. Association between Cardiovascular Disease and Liver Disease, from a Clinically Pragmatic Perspective as a Cardiologist. Nutrients. 2023;15(3):748. Published 2023 Feb 1