Storage of vitamins and minerals

The liver acts as a storage site for some vitamins, minerals and glucose. These provide a vital source of energy for the body which the liver transforms into glycogen for more efficient storage (see ‘metabolism’). The liver stores vitamins and minerals for the times when they may be lacking in the diet. It can store enough vitamin A and vitamin B12 for four years, and enough vitamin D for four months.

Vitamins

Vitamins are a group of organic compounds that act as catalysts in various chemical reactions. The vitamins trigger these reactions and speed them up. A compound becomes classified as a vitamin when a lack of it causes disease. 

Contrary to popular belief, vitamins do not directly provide energy. As catalysts, vitamins are required for the release of energy from protein, fat and carbohydrates. They are essential for normal growth and development and particularly important for the healthy functioning of red blood cells, hormones, genetic materials and the nervous system. 

The liver stores vitamin A, D, E, K and B12. The first four of these are all fat soluble. This means that the bile secreted during digestion is essential for absorbing them so that the body can use them. If bile production is compromised by liver damage, the proper absorption of these vitamins may be affected. 

When taking multivitamins it is important to make sure the recommended doses of fat soluble vitamins are not exceeded. If this occurs, it might result in liver damage.

Minerals

The liver also stores iron and copper. Copper is essential as a vital link in many of the body’s different chemical reactions and in the formation of protein within the liver. It also plays a role in using up the body’s iron stores, whenever they are needed. 

Page: The liver and metabolism

The word metabolism originated from the Greek word ‘to change’. In relation to the liver, it refers to the processing of food digested by the stomach and intestine for its many uses by the body.

We get our energy and build our cells and tissues using the energy given off from the breakdown of three major classes of nutrients. 

These are carbohydrates (simple and complex sugar), lipids (various fats and oils) and proteins (large molecules found in plant and animal tissues made up of amino acids). The liver plays an essential role in the breaking down of all of these types of nutrients and converting them into substances essential to the body. This process is called metabolism.

Carbohydrate metabolism

Glucose (or blood sugar) is made when carbohydrates are broken down. It is an essential energy source for all cells. Although we often eat at irregular intervals, the energy supplied to the body’s cells remains constant. The liver plays a crucial role in this process. If more glucose is absorbed than the body needs at that moment, the excess is turned into a substance called glycogen. This is then taken up by the liver for easier storage.

When blood concentrations of glucose begin to drop and the body needs to generate more energy and heat, the liver converts the glycogen back into glucose. It is then released back into the blood for transport to all other tissues.

The liver’s glycogen stores are limited. But when the supply of glycogen begins to run out the liver cells begin to produce glucose out of amino acids and other carbohydrates.

If the synthesis and storage of glucose is reduced by liver damage, the blood sugar levels may be affected. This can lead to insufficient amounts of energy reaching the muscles and the brain. This can then result in fatigue, a general sense of feeling unwell or slowed thinking and memory recall.

Fat metabolism

Fats or lipids are broken down in the liver for use as energy. They are then moved to fat tissue. More than 90% of body energy is stored here and is the main source of fuel storage for the body.

Fats are insoluble in blood and water and so the liver produces special, fat-carrying proteins called lipoproteins. These lipoproteins circulate in the blood, carrying essential fatty acids between the liver and body tissues.

The liver stores very little fat for its own use. Chronic hepatitis C can lead to an accumulation of fatty deposits in the liver. This condition is called ‘steatosis’ (Link to page). It is thought to be linked to increased fibrosis progression and advanced liver damage. It can also cause a decreased response to treatment for hepatitis C.

The lipoproteins also transport cholesterol. Although cholesterol has a certain ‘unhealthy’ reputation, it is still essential for the correct functioning of the body. It is used to make bile salts, to synthesise vitamin D, to make sex hormones, to make other hormones for the immune system and in dealing with stress. Cholesterol is also vital for the health of nerve cells and for the brain.

Cholesterol only becomes a problem when it builds up in the body in places it should not be. A healthy liver ensures that it is transported to tissues where it is needed and away from the tissues where it is not needed and may cause damage.

If the liver is not functioning properly or is over-burdened by cholesterol, fatty deposits containing cholesterol build up in the lining of arteries. These deposits can cause an obstruction to the blood flow and can also lead to heart attacks. They can also lead to a build-up of cholesterol in bile which can result in the formation of gallstones.