Sodium

Concentration differences between extracellular sodium and intracellular potassium help to create an electrochemical gradient across cell membranes known as the "membrane potential". The maintenance of cell membrane potential facilitates uptake of nutrients and expulsion of waste products by all cells, and the processes of muscle contraction and nerve impulse generation. As sodium determines extracellular fluid volume, including blood volume, it also serves to regulate blood pressure via hormone signalling. Sodium also contributes to the absorption of glucose and amino acids in the small intestine. 

Minimum requirements for sodium are currently unknown but have been estimated to be as low as 200 mg / day. Whilst public health recommendations stipulate that average salt intake be maintained at < 6 g per day, actual consumption in Western diets may be as high as 10 – 12 g (4 -5 g sodium) per day, far in excess of estimated requirements.

Note that approximately 3 g of daily salt intake is naturally contained in foods consumed, 3 g is added during processing, and 4 g is added by the individual. Increased reliance on restaurant eating, fast food and commercially prepared convenience food is also thought to contribute to high salt intake. The healthpro dietitians recommend restaurants and food providers affiliated to our healthy dining finder, where salt and sodium content have been quantified for your convenience. 

The major food source of sodium is sodium chloride (Na⁺Cl^-), more commonly known as table salt. Protein foods such as meats generally contain more naturally existing sodium than vegetables and grains, whereas fruits contain little or none.

The addition of table salt, flavoured salt, flavour enhancers such as soya sauce or fish sauce, and preservatives during food processing accounts for the high sodium content of convenience and fast food products.

As maintenance of sodium balance has been demonstrated at intakes less than 460 mg / day in some studies, deficiency as a result of inadequate dietary intake is unlikely. Hyponatraemia (defined as a serum sodium concentration < 136 mmol/L) may occur however, due to a range of factors;

• inappropriate anti-diuretic hormone (ADH) secretion, due to central nervous system disorders or use of medications such as diuretics or NSAIDs
• some forms of kidney disease
• prolonged or severe vomitting or diarrhea
• incorrect hydration during extended endurance exercise

The symptoms of hyponatraemia include headache, nausea, vomitting, muscle cramps, disorientation, and fainting. Severe hyponatraemia may result in cerebral oedema, seizures, coma, and brain damage, and may be fatal without appropriate medical intervention.  

High sodium / salt intakes disrupt the electrolyte balance of the body and may increase blood pressure and risk of stroke.  

It is thought that potassium and chloride counteract the uptake of sodium.

Vitamin D is thought to help the uptake of sodium.