Sodium

Functions

Sodium is a mineral that is essential for life. Sodium is the primary regulator of fluid volume outside of body cells (extracellular fluid); approximately 95% of our body's sodium is found in our extracellular fluid. Sodium and its fellow electrolyte chloride both play an important role in maintaining the concentration and charge differences across cell membranes that contribute to an electrochemical gradient called a 'membrane potential'. Sodium also plays an important part in the absorption of chloride, amino acids, glucose and water from our small intestine.

Role in Disease Prevention

Hypertension and Cardiovascular Disease

A minimum level of sodium is required in our diets, however unlike most other essential minerals it is not a deficiency but rather an excessive intake of salt (sodium chloride) that is of most concern in regards to increased disease risk. Considerable evidence from epidemiological, intervention and genetic studies suggests that chronically high salt intake can cause high blood pressure or hypertension (hypertension is defined as a diastolic blood pressure of 90mmHg or greater and a systolic blood pressure of 140mmHg or greater). Hypertension is a major risk factor for stroke, heart attack, heart failure and a number of other health conditions such as renal disease.

The exact mechanism by which chronic salt intake increases blood pressure is not yet fully understood. What is known is that with age we tend to become more 'salt sensitive', that is, the same level of salt intake in an older adult causes a greater increase in blood pressure than in a younger adult. However, normal blood pressure cannot be regarded as a 'sign' that our dietary salt intake is at an acceptable level; as excessive salt intake also increases the risk of negative effects on our cardiovascular system independently of blood pressure. High salt intake can increase arterial thickness/stiffness, cardiac left ventricle mass, and increases the risk of strokes as well as the severity of any cardiac failure.

Food Sources

Sodium is primarily found in food in the form of sodium chloride, otherwise known as table salt. Sodium is also present in the diet as sodium bicarbonate and monosodium glutamate, as well as being present in small amounts in other food additives. However, salt is by far the greatest contributor to dietary sodium intake.  Foods high in salt include many processed foods such as tinned soups, pasta sauces, packet gravies and sauces, vegetable/chicken/beef stocks, sausages/salami, cheeses and many asian style sauces such as oyster sauce, soy sauce, black bean sauce, fish sauce. 

Typical Contributions from Food

Food	Sodium (mg)
Soup, canned, tomato (1 cup)	1060mg
Pasta sauce, tomato (1 cup)	1210mg
Cheese, colby (20g)	136mg
Cheese, processed, sliced (1 slice)	355mg
Chicken stock, (1 cup)	920mg
Gravy (1/2 cup)	765mg
Sausage, beef (one)	679mg
Soy sauce, (1 tblsp)	1140mg
Oyster sauce (1 tblsp)	609mg
Fish sauce (1 tbsp)	1890mg

Source: The Concise New Zealand Food Composition Tables 5th Edition.

Adequate Intake (AI) Levels

There is currently insufficient data available to set a 'recommended dietary intake' level for sodium. Hence, only an indication of what would be considered an 'adequate' intake level is provided. Following are the adequate intake (AI) levels for New Zealand and Australia. 

Sodium AIs – New Zealand and Australia

Life Stage	Age	Males (mg/day)	Females (mg/day)
Children	1-3 yr	200-400	200-400
	4-8 yr	300-600	300-600
	9-13 yr	400-800	400-800
	14-18 yr	460-920	460-920
Adults	19 - 50 yr	460-920	460-920
	51 - 70 yr	460-920	460-920
	70+ yr	460-920	460-920
Pregnant	14-18 yr	-	460-920
	19+ yr	-	460-920
Breastfeeding	14-18 yr	-	460-920
	19+ yr	-	460-920

Upper Level of Intake

It is recommended that sodium intake in adults is limited to a maximum of 2300mg/day. This level has been set with reference to sodium's effects on blood pressure. An intake of 2300mg/day in adults will result in hypertension in less than 2% of the population. Ideally, however, a lower intake of sodium is recommended, see the suggested dietary target for reducing chronic disease risk below.

Suggested Dietary Target for Reducing Chronic Disease Risk

The New Zealand and Australian governments have set a suggested dietary target (SDT) for sodium intake of 1500mg/day for men and women. There is some evidence to suggest that this lower level of sodium intake may reduce the risk of hypertension and its sequelae in the general population. This lower SDT target is provided for the information purposes of individuals and is based on current scientific evidence relating diet to chronic disease risk.

Deficiency - Hyponatremia

Sodium deficiency, or hyponatremia, is not typically the result of insufficient dietary intake of sodium, rather it typically results from excessive fluid retention or sodium excretion. Various medical disorders such as prolonged vomiting, diarrhoea and sweating can be a cause, as can kidney disease. The use of medications such as diuretics can also cause problems with sodium balance.

Excessive water intake can also result in dilutional hyponatremia, symptoms of which include headache, nausea, vomiting, muscle cramps and fatigue before progressing to disorientation, fainting and ultimately swelling of the brain, seizures, coma and brain damage. Hyponatremia is a very real problem in long-distance running, suggesting that either fluid excretion is altered in this type of situation or that the individuals fluid intake during the event was far in excess of requirements.

References

Garrow JS, James WPT & Ralph A. (2000). Human Nutrition and Dietetics (10th Ed). London: Churchill Livingstone.

Ministry of Health. (2006). Nutrient reference values for Australia and New Zealand. Canberra: Commonwealth of Australia.

 

Last Updated: 9 October 2008

The material provided by Thinking Nutrition Ltd on this website is for information purposes only. It is not a substitute for appropriate health advice from a qualified medical practitioner.