Sodium

Sodium is a silver-white alkali metal that is highly reactive in air and with water. It has the atomic number 11 and the chemical symbol Na. It was discovered and described in 1807 by the English chemist Sir Humphry Davy (1778- 1829) in London. It is mainly found in seawater and in salt deposits as sodium chloride. In technology, sodium is used as a coolant in a number of nuclear reactors, among other things. It is the 6th most common element in the earth's crust, ahead of potassium. However, due to its chemical reactivity, it does not occur in its pure form, but only in various compounds. Alongside chlorine, sodium is one of the two components of sodium chloride (table salt). In earlier centuries, salt was a very valuable and expensive spice that was also used to preserve food, mostly meat. Another well-known and important sodium compound is soda (sodium carbonate, Na2CO3), which is used, among other things, as a leavening agent and is partly responsible for the fizziness of mineral water. Sodium hydroxide (NaOH) is an alkali found in detergents and is highly corrosive to the skin in its pure form. In medicine, sodium is one of the bulk elements. It regulates the body's water balance, osmotic pressure, acid-base balance, ensures the excitability of muscles and nerves and activates various enzymes. The human body contains around 80-100 g of sodium, 30%-35% of which is stored in the bones.

Functions in the body

Sodium is mainly present in the body fluid outside the cells in a concentration of around 140 millimoles per liter (mmol/l) = 3.22 g/l. The intracellular concentration is around 10 mmol/l = 0.23 g/l. The most important functions of sodium are the regulation of the water balance, the acid-base balance and the osmotic pressure of the cells in the body, in which it prevents excessive water loss, which can lead to dehydration. Sodium is also needed to support a number of enzymes. Sodium also plays a crucial role in the transmission of electrical impulses in nerves and muscle cells, as well as in the contraction of muscles, including the heart.

For those who are particularly interested, this process can be explained as follows: The cells of the heart, like skeletal muscle cells, have an electrical voltage between the inside and outside of the cell. In skeletal muscle, the voltage between the inside and outside of the cell at rest is approx. -90 mV (mV = millivolts), in the heart approx. -70 mV, whereby the inside of the cell is negatively charged compared to the outside. The main reason for this voltage is the property of the cell membrane to have different permeabilities for the various ions present in the body. This permeability of the membrane can be changed by means of chemical, mechanical or electrical stimuli. A skeletal muscle maintains its electrical voltage permanently without external stimuli, e.g. nerve stimulation. This is different in the cells of the heart. To generate a voltage of -70 mV in the heart, there is a difference in concentration of Na+ ions between the inside and outside of the cell of around 1:14 and of K+ ions of 35:1. There are also differences in concentration for Cl- and a number of other ions.

In contrast to skeletal muscle cells, the resting potential of -70 mV is not stable in heart cells. Small amounts, especially Na+, enter the cell interior. This leads to a reduction of the voltage from -70 mV inside the cell to more positive values of e.g. -60 mV. The more positive (= less negative) the cell interior becomes, the greater the permeability of the cell membrane for Na+ and the more positive the cell interior becomes. From a so-called threshold at around -50 mV, the permeability of the cell membrane changes very quickly, so that relatively more Na+ can flow in within a very short time. This leads to a voltage reversal of +30 mV compared to the cell exterior.

During this process, the Na+ permeability then decreases again and that for K+ and Cl- increases. K+ flows out of the cell and Cl- flows in. This happens until the original state is restored, i.e. the inside of the cell has a voltage of around -70 mV again. It should be mentioned that the extremely small quantities of Na+ ions that flow into the cell and the K+ ions that flow out are transported out or in again and again by so-called active processes.

Foods containing salt

Salt is contained in almost all foods. The additional use of table salt means that there is an abundant supply. Salted herrings, for example, contain almost 6 g of salt per 100 g, while olives contain around 2 g of salt per 100 g.

Deficiency symptoms

An extreme loss of electrolytes - especially sodium, potassium and calcium - during vomiting and diarrhea can lead to a life-threatening imbalance of the water balance in infants and small children as well as in the elderly. Symptoms of a sodium deficiency include a lack of energy, listlessness, confusion and, in extreme cases, unconsciousness. Other signs may include low blood pressure, nausea, vomiting, dizziness, loss of appetite and headaches. Heart palpitations, dehydration, i.e. dehydration of the tissues, as well as muscle weakness, muscle cramps or muscle pain may also occur.

Overdose

The intake of too much salt and therefore sodium is considered relatively harmless as it is excreted via the kidneys. For a long time, a long-term excessive intake of sodium was associated with a predisposition to cardiovascular disease, but this connection has recently been partly disputed. Nevertheless, patients with high blood pressure are recommended to eat as little salt as possible. Low-sodium salt substitutes are available in pharmacies for this purpose. People with kidney disease, especially dialysis patients, must always pay strict attention to a controlled sodium balance. However, there now seems to be strong evidence that consuming too much salt can increase the risk of stomach cancer. At the beginning of 2004, the British Center for Cancer Research pointed out on the basis of a Japanese study that the risk of stomach cancer roughly doubles with a daily intake of 12-15 grams of salt.

Requirements

The German Nutrition Society specifies a daily requirement of 550 mg for adolescents and adults. More is usually consumed as sodium, as sodium chloride, is found in almost all foods and is also used for salting. The daily intake of sodium varies greatly from person to person and depends on seasoning and eating habits. It is estimated that the daily intake of salt in Germany is around 8 g. There is an increased need for sodium in cases of diarrhea (diarrhea), vomiting (especially in children) and very heavy sweating. In this context, it should also be mentioned that competitive athletes have an increased sodium requirement. However, there are also diseases, such as some liver and kidney diseases or cystic fibrosis, which can lead to an increased need for sodium.

Requirements in sport

Athletes have a higher sodium requirement (3-4g per day), mainly because there is a greater loss of sweat during training. One liter of sweat contains 1-1.5g of sodium, depending on the level of training (trained people excrete fewer minerals with their sweat). It is also assumed that creatine is also absorbed by the muscles in a sodium-dependent manner, so that a sufficient supply of sodium can also be recommended to the athlete from this point of view.