The Complete Book of Men's Health - Part 3: Nutrition and Lifestyle

IODINE

Iodine is essential for the synthesis of thyroid hormones.

• EC/UK RDA: 150 mcg/day.

• US RDA: 150 mcg/day.

• Athletes may need more as they can lose up to 150 mcg per day in sweat.

• UK average intake: 237 mcg/day. Intakes range 100­420 mcg.

• Sports nutritionists prescribe iodine supplements containing 50­200 mcg per day for some athletes. These levels are not toxic, though supplements containing more than this may make acne worse.

Iodine deficiency is now rare in Western countries since the introduction of iodized salt. In parts of the world, however (e.g. central Brazil and the Himalayas) thyroid gland goitres due to iodine deficiency affect up to 90 per cent of the population.

• Foods rich in iodine include:

marine fish

seafood (e.g. shrimp, lobster)

seaweeds

iodized salt.

• In the UK, cow's milk is also a good source due to the iodization of cattle feed.

IRON

Iron is an essential element for the combustion of carbo-hydrate, fat and protein to produce energy. It also forms part of the haemoglobin molecule which carries oxygen in the blood, and myoglobin, which binds oxygen in muscles.

• EC/UK RDA: 14 mg/day.

• US RDA: 10 mg/day.

• UK average intake: 13.7 mg/day. This varies from 6.5­25.7 mg from food sources.

• Sports nutritionists sometimes prescribe iron supplements of 10­25 mg per day for athletes in training. More than this is liable to have side-effects, and iron is toxic in high doses.

• Foods rich in iron include:

red meat

poultry

fish

nuts

wholemeal bread

cocoa

egg yolk

green vegetables

parsley.

• The form of iron (heme) that is most easily absorbed is in red meat. Non-heme iron from vegetables is up to 10 times less bioavailable. Overboiling vegetables decreases their iron availability even further.

Vitamin C increases the absorption of iron, while calcium and tannin-containing drinks (e.g. tea) decrease it. Iron supplements taken alone can also decrease the absorption of dietary zinc, manganese, chromium and selenium.

MANGANESE

Manganese is another important antioxidant that is a component of several enzymes protecting against free radical attack (see Chapter 21). It is necessary for the synthesis of blood-clotting factors, cholesterol and the brain neurotransmitter dopamine. Research also suggests it is involved in glucose metabolism and the maintenance of normal bone structure.

• The optimal intake of manganese is unknown, but on average we excrete 4 mg manganese per day which needs to be replaced.

• US National Research Council suggested intake: 2­5 mg/day. Up to 10 mg/day is considered safe. There is no EC/UK RDA.

• Because of their higher metabolism of glucose and the increased mineralization of bone, athletes may need more than this. Some sports nutritionists prescribe supplements containing 2­5 mg manganese.

• UK average intake: 4.6 mg.day (half of this derived from tea). One cup of tea contains around 1 mg of manganese. American men, who tend to drink less tea, obtain an estimated 2.7 mg manganese per day.

• There is no evidence of toxicity ­ in fact, manganese is considered one of the least toxic minerals when taken orally. If excess is consumed in the diet, absorption is low while excretion (via bile and kidneys) is high.

• Foods and drinks rich in manganese include:

tea

whole grains

nuts

fruits

seeds

yeast

egg

leafy, green vegetables/herbs ­ depending on the manganese content and acidity of the soil in which they were grown.

• Small amounts of manganese are obtained from meat, shellfish and milk.

SELENIUM

Selenium is another powerful antioxidant that works in conjunction with vitamin E to help protect against free radical attack. It is essential for cell growth and fighting infection.

• EC/UK RDA: 75 mcg/day.

• US National Research Council recommendation: 70 mcg/day.

• UK average intake: 65 mcg/day, with 50 per cent obtained from cereals. Meat and fish provide most of the rest.

• Athletes may need more as exercise generates free radicals. Excess selenium can be toxic. An upper safe limit of 450 mcg per day has been suggested for adult men. If supplements are used, they should contain between 50 and 400 mcg selenium and no more, unless prescribed under medical supervision. Additional vitamin E should also be taken. Interestingly, inorganic selenium (but not organic) is best taken separately from vitamin C as the latter may impair selenium absorption.

• Foods rich in selenium include:

broccoli

mushrooms

cabbage

radishes

onions

garlic

celery

fish

wholegrains

wheat germ

nuts

yeast. A selenium-enriched strain of organic yeast is now commercially available.

In some countries, selenium deficiency is widespread. Lack of selenium in the soil does not affect plant growth but causes a muscle-wasting disease in grazing animals. In China, intakes of selenium are less than 12 mcg per day, this lack of selenium has been associated with an endemic weakness of heart muscle (Keshan Disease) which is responsive to selenium supplementation.

In parts of the US, New Zealand and Finland, selenium is added to fertilizers to increase population intakes. Average selenium intakes among New Zealand men are 15­40 mcg per day, although no selenium-responsive disease has so far been identified.

ZINC

Zinc is another antioxidant mineral that is an important co-factor for over a hundred enzymes. It is needed to switch on certain genes in response to hormone signals. This initiates synthesis of the specific protein that gene is responsible for making; zinc therefore plays an important role in the sensitivity of tissues to hormones.

Zinc deficiency before puberty delays sexual development and can result in smaller male sex organs. Deficiency in later life leads to slowed muscle growth and impaired immunity to disease. More severe deficiencies lead to loss of the sense of taste, and muscle weakness.

• EC/UK RDA: 15 mg/day

• US National Research Council recommendation: 15 mg/day.

• UK average intake: 11.4 mg/day. Intakes range from 5.7­19 mg/day.

• Athletes need more zinc than sedentary men due to their higher fatty acid turnover, to replace zinc lost in sweat, and for the interaction of testosterone which helps initiate muscle growth. Some sports nutritionists prescribe supplements containing 15­50 mg zinc per day for athletes.

• It is worth knowing that taking any more than 10 mg zinc in one go can upset the stomach and cause nausea. Zinc seems safe at doses up to several hundred milligrams per day, but excess impairs copper metabolism.

• Foods rich in zinc include:

oatmeal

whole grain products

yeast

seafoods

meat

nuts

milk

eggs

cheese.

Moderate amounts of zinc are found in chicken and vegetables. In general, animal meat is a better source of bioavailable zinc than vegetables.

You can check your zinc levels by obtaining tests from a pharmacy. If your zinc levels are low, taking supplements of 10 mg zinc three times a day will cause a rapid improvement. If you find this level in zinc intake causes gastrointestinal symptoms, drop down to taking the supplement twice a day.

Soya products and foods rich in iron reduce the absorption of zinc from the digestive tract. They are best avoided within two hours of taking your zinc supplements.

BORON

Boron seems to be essential for the manufacture of some steroid hormones, especially those needed for optimal muscle growth.

• UK average intakes: 0.4­1.9 mg/day.

• Optimal intake: unknown. Suggestions of 2 mg/day have been made.

• Some sports nutritionists prescribe supplements containing 3­6 mg per day.

• Intakes above 50 mg per day may impair the metabolism of other nutrients.

• Foods rich in boron include fruits and vegetables, especially:

soybeans

peanuts

almonds

raisins

prunes

dates

• raw honey.

Claims that boron can increase testosterone levels and build muscle are misleading. They are based on studies in post-menopausal women ­ not in hefty young athletes. Increased testosterone levels would only be expected in men if gross boron deficiency prevented the body making its normal amount.

MOLYBDENUM

Molybdenum is a co-factor for three enzymes, one of which is involved in the metabolism of alcohol.

• UK average intakes: 70­240 mcg/day.

• Optimal intake: unknown. Provisional recommended intakes are between 75 and 250 mcg per day. There is no evidence that

athletes need more than this.

• Intakes above 500 mcg (0.5 mg) cause the loss of excess urinary copper, while doses above 10 mg per day can trigger gout.

Molybdenum deficiency has been linked with a high incidence of oesophageal cancer in China.