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Quest Vitamins LTD,
8 Venture Way,
Aston Science Park,
B7 4AP.

Tel: 0121 359 0056
Fax: 0121 359 0313
Registered in England No. 2530437

Issue # 66.10 - A-Z of Nutrition

A to Z of Nutrition: Magnesium Quantitatively

Magnesium ranks next to phosphorus and calcium in the body. Magnesium is intimately involved with calcium in metabolism.

What does it do?

More than 65% of the magnesium content of the body is found in the bone, where along with calcium and phosphorus it provides structure and strength. The mineral plays a vital role in energy release, as it is a cofactor in energy-producing reactions. It is also needed in RNA synthesis and in DNA replication - i.e. in cell production. Additionally, magnesium is important in the functioning of nerves and muscles

What are the deficiency signs?

Possible manifestations of magnesium deficiency include muscle cramps and twitches, insomnia, irritability, rapid heartbeat, low blood sugar and anxiety.

Is it toxic?

There is no evidence to suggest that large intakes of magnesium are harmful to humans with normal kidney function. Excessive circulating levels of magnesium are almost impossible to achieve by ingestion from foods, but high levels induced by intravenous administration can interfere with nerve transmission and are therefore very dangerous. Carcinogenicity may occur at doses of 3000mg/kg body weight which amounts to 195g per day based on a 65kg human. 3-5g of magnesium salts have a purgative action and is harmful if taken frequently for this purpose.

Who should supplement?

Magnesium is often taken by women to ease PMT, especially stomach cramps and sugar cravings. The use of magnesium in this situation makes a lot of sense because tests have borne out that blood magnesium levels do drop before a period. Other conditions in which magnesium has been found to be helpful are involuntary muscle twitches (of the eyelid for example) and combined with calcium for muscle cramps. Again in relation to muscle function, it is also thought that magnesium has some protective effect on the heart, perhaps more particularly in the prevention of arrhythmias (irregular heart beats)

Intake levels

Milligrams (mg) RDA 300 Upper safe level

(long term)300

(short term) 400

Which foods?


Peanuts, roasted 180

Bread, wholemeal 76

Cheese, cheddar 25

Fish, white 23

Chicken 21

Potatoes 17

Oranges 13

Eggs 12

A to Z of Nutrition: Selenium

Now regarded as an essential trace element in humans and animals, selenium is found in uneven quantities in parts of the earth's surface. Selenium toxicity has been noted in areas where selenium content of the ground is high, but selenium deficiency is a far more widespread problem - contributing to infertility, heart problems, eye disease and premature ageing.

What does it do?

Selenium carries out its main functions as part of the enzyme glutathione peroxidase. Glutathione peroxidase is an antioxidant that protects intracellular structures against oxidative damage by free radicals.

Selenium is known to have a role in the following:

Preservation of normal liver function.

Antioxidant protection of all body cells.

Maintenance of a healthy heart.

Inhibition of harmful effects from heavy metals such as arsenic, cadmium, mercury and lead.

Production of beneficial anti-inflammatory prostaglandins.

Production of thyroxine hormone.

What are the deficiency signs?

Selenium deficiency has traditionally occurred in areas where the soil is particularly low in this mineral. However, as modern lifestyles have allowed us to eat foods from very many different countries of origin, true selenium deficiency has become less of a problem.

One selenium deficiency disease is known as Keshan's disease - after the province in China that has the lowest soil selenium levels in the world. Symptoms are mainly to do with the heart - specifically involving wastage of the heart muscle.

Another selenium deficiency disease is known as Kaschin-Beck disease, and affects the cartilage in the joints.

Is it toxic?

Evidence of disturbed selenium regulation occurs at intakes above 750?g and deterioration and loss of nails have been noted in adults ingesting 900?g per day

Who should supplement?

The groups of people particularly found to be at risk of selenium deficiency are as follows:


The elderly

Pregnant and nursing mothers


Rheumatoid arthritis sufferers

Intake levels

There is no EC Recommended Daily Allowance for selenium. Upper safe level 200 ?g

Which foods?


Organ meats 40

ish and shellfish 32

Meat 18

Wholegrains & cereals 12

Dairy products 5

Fruit and vegetables 2

A to Z of Nutrition: Zinc

The zinc content of the adult body is approximately 2-3g, and the mineral is found most highly concentrated in muscles, liver, kidneys and eyes. In males, zinc is also present in large amounts in the prostate gland and sperm. A component of over eighty enzymes, zinc functions in many reactions in the human body.

What does it do?

Zinc is necessary for normal cell division and function. It is found in alpha-macroglobulin, an important protein in the body's immune system and is needed for the functioning of the thymus gland. It is necessary for the growth in children and maturation of the sex organs at puberty. The mineral is also needed for the production of male sperm and female ova. Zinc helps clear certain toxic metals from the body (e.g. cadmium and lead). Zinc is also essential for the maintenance of vision, taste and smell; for the release of insulin and for the absorption and metabolism of vitamin A

What are the deficiency signs?

The deficiency signs of zinc are frequent infections, delayed wound healing, reduced appetite, decreased sense of taste or smell, skin disorders, and white marks on nails.

Is it toxic?

After acute ingestion of 2g or more of zinc, symptoms such as nausea, vomiting and fever develop. Long term intakes of around 75-300mg of zinc are associated with features of copper deficiency such as neutropenia (low levels of neutrophil type of white blood cell) and anaemia.

Who should supplement?

A supplement of zinc may be helpful in the following situations:

Those with skin conditions i.e. acne and eczema

Those with inflammation of the prostate

Those with slow wound healing

Those with high alcohol intake

For increased fertility

Intake levels:

milligrams (mg) RDA 15

Upper safe level (long term) 15

(short term) 50

Which foods?


Cheese Cheddar 4.0

Beef, stewing steak 3.8

Lentils 3.1

Bread, wholemeal 1.8

Eggs 1.5

Chicken 1.1

Bread, white 0.6

Fish, white 0.4

Milk 0.4

Potatoes, old 0.3

References 1. Vitamin and Mineral Safety, Council for Responsible Nutrition: 1997 2. Health Essentials, Vitamin Guide: 1994 3. Manual of Nutrition (MAFF):1989

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