NUTRITION: MINERALS

MINERALS

Minerals are essential for healthy and active lifestyles and are classed as major or trace minerals according to their contribution to our health. Minerals serve as constituents of enzymes, hormones and vitamins. They help in body structure (bones & teeth), function (maintaining heart rhythm, muscle contractility..), and help regulate cellular metabolism as parts of enzymes and hormones. They also combine with other chemicals such as calcium and phosphate in bones or exist singularly, e.g. calcium in body fluids. A summary of their various sources, deficiencies, excesses etc are shown below. The precise nature of minerals (not mentioned in this list) such as boron, nickel, molybdenum, lithium is still relatively unknown.

Major Minerals
Mineral	RDA(mg) M	RDA(mg) W	Dietary Sources	Body Functions	Deficiency	Excess
Calcium	1200 (800mg for adults 25+)	1200	Milk, cheese, yoghurt, canned fish are rich sources, dark green leafy vegetables	Bone & teeth formation, blood clotting, nerve transmission	Stunted growth, rickets, osteoporosis, convulsion	Not reported in humans
Phosphorous	1200 (800 mg for adults 25+)	1200	Milk, cheese, eggs, meat, fish, grains	Bone & teeth formation, acid-base balance	Bone weakness Loss of calcium & demineralisation of bone	Erosion of jaw
Potassium	2000	2000	Most foods, leafy vegetables, potatoes, bananas, milk, meat, coffee, tea	Fluid balance, nerve transmission, acid-base balance	Cramps, irregular cardiac rhythm, confusion, loss of appetite, can be life-threatening	None if kidneys function correctly, if poor kidney function, potassium build up and cardiac rhythm problems
Sulphur	Unknown	Unknown	Obtained as part of dietary protein	Acid-base balance, liver function	Unlikely with adequate diet	Unknown
Sodium	1100-3300	1100-3300	Common salt & occurs naturally in many food types	Acid-base balance, body function, nerve function	Muscle cramps, mental apathy, reduced appetite	High-blood pressure
Chloride	700	700	Part of salt containing food, some vegetables and fruit	Important part of extracellular fluids	Unlikely with adequate diet	With sodium leads to high blood pressure
Magnesium	350	280	In most foods, whole grain cereals, nuts, spinach	Involved in enzyme activation in protein synthesis	Growth failure, disturbances in, behaviour, spasms, weakness, hinders training adaptation	Diarrhoea
Trace Minerals
Mineral	RDA (mg) W	RDA (mg) M	Dietary Sources	Body Functions	Deficiency	Excess
Iron	10	15	Red meat, offal, eggs, bread, cereals, flour, vegetables	Constituent of haemoglobin & enzymes involved in energy metabolism	Iron deficiency, anaemia, weakness, decreased resistance to infection	Siderosis, Cirrhosis of liver
Fluoride	1.5-4.0	1.5-4.0	Tea, fish, fluoridated water, toothpaste	Maintaining bone structure	Tooth decay	Teeth Mottling, increased bone density, neurological disorders
Zinc	15	12	Milk, cheese, eggs, meat, fish, whole-grain cereals, pulses	Constituent of digestive enzymes	Growth failure, small sex glands	Fever, nausea, vomiting, diarrhoea
Copper	1.5-3.0*	1.5-3.0	Fish, green vegetables, liver, meats, drinking water	Constituent of enzymes within the iron metabolism	Anaemia, bone changes	Rare metabolic condition (Wilson's disease)
Selenium	0.070	0.0055	Cereals, meat, fish, offal, cheese, eggs, grains	Functions with Vitamin E	Anaemia (rare)	Gastrointestinal disorders, lung irritation
Iodine	150	150	Fish, dairy products, vegetables, iodised salt, seaweed	Constituent of thyroid hormones	Goitre (enlarged thyroid)	High intakes depress thyroid activity
Chromium	0.075-025*	0.05-0.25*	Nuts, prunes, dark green vegetables, corn, vegetable oils, orange juice, meat	Constituent of some enzymes, involved in glucose & energy metabolism	Impaired glucose metabolism, not reported in humans	Inhibition of enzymes, skin & kidney damage

These are recommended values (revised 1989) from the Food & Nutrition Board, National Academy of Sciences-National Research Council, Washington D.C for Men (M) and Women (W).

* Because there is less information on which to base allowances, these figures are given in the form of ranges.

In general, no vitamin-and-mineral supplements should be required if an athlete is consuming a a variety of foods to cover their energy expenditure. Even though minerals are lost through sweating, sweat loss during exercise usually does not increase mineral requirements above normal values and these can be replaced through correct post-exercise eating and drinking. Furthermore, there is no real evidence that mineral supplements improve exercise capacity. For more information on nutritional supplements click here. However, there are some athletes who may be at risk. For example, sports women who train intensely, often do not match energy intake to energy output or have a lack of dietary iron or calcium due to them trying to reduce their daily energy intake. No single nutrient supplements should be used without a specific medical or nutritional reason (e.g., iron supplements to reverse iron deficiency anaemia).

Many foods such as fortified breakfast cereals and breads have various vitamins and minerals added to them. Therefore, if the diet is low on fresh fruit and vegetables for short periods of time, these fortified foods can help briefly cover the deficit in these essential ingredients. If energy intake is too low (e.g. through a busy lifestyle where meals are regularly missed), then even a balanced diet will not cover the daily health requirements for the recovery, growth and repair of tissues. Studies carried out on German International soccer players demonstrated that their food intake was lacking in the necessary vitamins and minerals needed to maintain physical and mental performance, especially during intense competition and training. This indicates the need for good nutritional habits even at the highest levels of soccer.

Click here to go to the nutrition advice section of Soccer Performance.

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