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

Vitamin B₆ (Pyridoxine)

Vitamin B₆ is needed for the proper functioning of over 60 enzymes and is involved in the synthesis and metabolism of nucleic acids, amino acids and proteins.

It is also involved in the burning of glycogen as fuel.

• EC/UK RDA: 2 mg/day

• US RDA: 2 mg/day

• UK average dietary intake: 2.5 mg/day. Observed intakes vary from 1­4.5 mg.

Some sports nutritionists recommend that athletes ensure an intake of 10 mg to 50 mg per day. More than this is not recommended. Supplements providing 100 mg to 500 mg vitamin B₆ per tablet are potentially dangerous if used without medical supervision.

• Foods rich in vitamin B₆ include:

meat

whole-grain cereals

nuts

yeast extract

vegetables.

Excessive vitamin B₆ (several hundreds of mg/day) taken over several weeks or months can produce symptoms of nerve damage (tingling, burning, shooting pains, pins and needles, clumsiness, numbness, even partial paralysis), depression, headache, tiredness, bloatedness and irritability. These symptoms are only partially helped by eliminating B₆ supplements from the diet.

More modest doses (100 mg/day for several months) cause less serious nerve damage, resulting in tingling sensations in the fingers and toes that goes away once supplements are discontinued.

Vitamin B₁₂ (Cobalamin)

Vitamin B₁₂ is an essential component of several coenzymes. It cooperates with another vitamin, folate, during the synthesis of genetic material (DNA) ­ a process that occurs continuously during muscular development and red blood cell formation. Deficiency of either vitamin leads to the formation of abnormal cells that are larger than they should be (megablastosis). Vitamin B₁₂ also plays a role in the formation of healthy nerve sheaths (myelin).

• EC/UK RDA: 1 mcg/day. Some countries recommend an adult intake of 3 mcg/day.

• UK average dietary intake: 7 mcg/day. Observed variations range from 2­23 mcg/day.

There is little evidence that athletes need much more than this observed average intake ­ although some nutritionists recommend intakes of up to 50 mcg for everyone, athlete or not. Most adults who eat meat products obtain at least 5 micrograms vitamin B₁₂ per day.

• Some athletes receive megashots of vitamin B₁₂ injections before competitions. There is no evidence that this practice is efficacious, although it does seem to be safe.

• Foods rich in vitamin B₁₂ include:

liver

fish (especially sardines)

meat

eggs

milk

cheese.

• No vegetables are known consistently to contain vitamin B₁₂ ­ an important point for vegetarian, especially vegan (lacto-vegetarian) men. Preparations of vitamin B₁₂ made by bacterial fermentation ­ and therefore acceptable to vegetarians ­ are readily available.

Vitamin B₁₂ deficiency is fairly common, but this is usually due to malabsorption from the intestine rather than dietary lack. It can result in pernicious anaemia. This is triggered when the body stops making intrinsic factor ­ a substance secreted in the stomach which is needed for the absorption of vitamin B₁₂ lower down the intestinal tract.

Folate (Folic Acid)

Folate is involved in the formation of coenzymes that control amino acid and sugar metabolism. It is needed for the synthesis of nucleic acids during cell division, and is vital for red blood cell formation.

Body folate stores are small and deficiency develops quickly ­ it is probably the most widespread vitamin deficiency in industrialized countries.

• EC/UK RDA: 200 mcg/day.

• US RDA: 200 mcg/day (300 mcg/day until recently)

• UK average daily intake for men: 308 mcg/day. Observed intakes vary from 145­555 mcg.

• There is no evidence that moderate supplementation with folic acid is harmful. There are two potential problems, however:

1. taking folate supplements alone may mask a vitamin B₁₂ deficiency, and the imbalance can lead to spinal cord damage.

2. anticonvulsant drugs to control epilepsy work by increasing folate metabolism (which can trigger deficiency). Taking folate supplements (greater than 1 g/day) may antagonize the beneficial effects of anticonvulsant drugs and increase the frequency of epileptic fits. Epileptic men on medication should discuss supplementation with their neurologist.

• Some sports nutritionists suggest that active athletes need 800­4,800 mcg folate to maintain adequate body supplies and optimum performance. This is only safe as long as pernicious anaemia due to vitamin B₁₂ deficiency or malabsorption has been ruled out.

• Foods rich in vitamin B include:

fish (especially sardines and oysters)

meats (especially liver, kidney and rabbit)

dairy products

wholegrain cereals

oranges

nuts

yeast.

• On average, men get most dietary folate from dark green vegetables (35 per cent), bread and flour products (26 per cent), meat products (10 per cent), milk products (9 per cent) and fruit (6 per cent).

NB Prolonged boiling destroys much of the folate present in green leafy vegetables.

Biotin

Biotin is a water-soluble vitamin. It acts as a co-factor for several enzymes involved in the synthesis of fatty acids, purine nucleotides (building blocks for DNA) and in the metabolism of some amino acids (valine, isoleucine and leucine). It is also essential for the formation of new glucose within the body and, as such, is especially important for athletes.

Biotin is widely distributed in food and is also synthesized by bacteria in our own intestines. The amount excreted in faeces is up to six times higher than that ingested in the diet. Deficiency is therefore rare except in people who eat large amounts of raw egg white ­ an important point for body-builders to note. Egg white contains a protein called avidin which binds to biotin synthesized in the digestive tract and prevents its absorption. Avidin is denatured by cooking, however, and loses its ability to bind biotin.

Men eating a poor diet who are also on long-term antibiotic treatment may be at risk of biotin deficiency, as may those following very low-calorie weight loss diets. Biotin deficiency leads to flaking skin, wasted muscles and hair loss.

• EC/UK RDA: 150 mcg/day (intakes between 10 and 200 mcg are thought to be both safe and adequate).

• US RDA: 100 mcg/day (until recently it was 300 mcg).

• UK average daily intake: 38.5 mcg/day. Intakes range from 15­70 mcg/day.

Although apparently low, these intakes do not seem to cause deficiency, presumably because of the dietary top up of biotin manufactured by intestinal tract bacteria.

• Some sports nutritionist suggest athletes in intensive training require 300­5,000 mcg/day to optimize protein and glucose synthesis. There is no evidence that excess biotin either improves athletic performance, or that it is toxic.

• Foods rich in biotin include:

liver

sardines

egg yolk

whole grains (especially soy)

nuts

milk

vegetables.

Vitamin C

Vitamin C is a water-soluble vitamin essential for the synthesis of collagen ­ a major structural protein important for combating sports injury ­ and for the synthesis of adrenaline and noradrenaline. These are important neurotransmitters with several roles in the body, including the fight-or-flight reaction.

Vitamin C also acts as an antioxidant to mop up dangerous free radicals produced by metabolic reactions. As such, an active sportsperson with a raised metabolic rate is likely to need more vitamin C than a sedentary male. Vitamin C is an important component of semen.

Vitamin C has an additional important role ­ that of regenerating the lipid-soluble antioxidant vitamin E from its oxidized form back into its protective, reduced form (see Chapter 21).

• Current recommendations for vitamin C intake vary widely:

• The Netherlands: 80 mg/day

• US RDA: 60 mg/day.

• EC/UK RDA: 60 mg/day.

• Smokers need at least 100 mg vitamin C per day to mop up the excess free radicals generated by their habit.

• Some sports nutritionists suggest athletes need as much as 2­12 g per day. There is little evidence of toxicity as, being water soluble, any excess vitamin C is voided in the urine. This seems to protect against bladder cancer. Certainly people who take megadoses of vitamin C seem to live longer and have a significantly reduced risk of coronary heart disease and cancer. A few people notice symptoms of diarrhoea if they take too much vitamin C.

• UK average dietary UK intake: 64.8 mg/day. Observed average intakes vary widely: 19­171 mg/day. It can be estimated that 60 per cent of adults do not obtain the EC recommended amount of 60 mg/day.

• Foods rich in vitamin C include:

blackcurrants

guavas

citrus fruits

mangoes

kiwi fruit

green peppers

strawberries

green sprouting vegetables (e.g. broccoli, sprouts, watercress) and potatoes.

• On average, we obtain 50 per cent of our daily intake from vegetables (19 per cent from potatoes), 17 per cent from fruit juice drinks and 14 per cent from fruits and nuts.

Large doses of vitamin C assist the absorption of dietary iron but may have adverse effects on the copper status of men. Whether or not this is significant is unknown. It is also poss-ible that taking vitamin C with inorganic selenium (see below) might make it less easily absorbed. Use selenium derived from yeast instead.

Vitamin D

Vitamin D stimulates synthesis of a calcium transport protein in the lining of the small intestines and is essential for the absorption of dietary calcium. Adequate amounts of vitamin D are needed for calcium balance and to maintain healthy bones and teeth.

Most of our vitamin D is synthesized from a cholesterol-like molecule in the skin due to the action of short wavelength ultraviolet light. Blood levels of vitamin D are naturally highest at the end of summer and lowest at the end of winter. People living in high altitudes, who cover up their skin in sunlight or who stay indoors all the time may have insufficient exposure to UV light to synthesize required amounts. Dietary sources are then critical.

• EC/UK RDA: 5 mcg/day.

• UK average dietary intake: 3.4 mcg/day. Intakes vary from 0.5­10 mcg.

• There is no evidence that athletes need more than 10 mcg per day. Amounts only five times this can be toxic. Those taking more than 250 mcg of vitamin D supplements develop high blood calcium levels leading to symptoms of thirst, anorexia, excess urine production and kidney stones. Toxicity only occurs through too much oral intake, not through exposure to sun, where synthesis is self-limiting.

• Foods rich in vitamin D include:

oily fish (sardines, herring, mackerel, salmon)

tuna

fortified margarine

eggs

whole milk

butter.

• On average, men obtain 32 per cent of dietary vitamin D from fortified fat spreads, 22 per cent from oily fish and 22 per cent from cereal products.

NB 1 mcg vitamin D (cholecalciferol) = 40 iu

Vitamin E

Vitamin E functions mainly as an antioxidant, mopping up dangerous free radicals formed during metabolism (see Chapter 21) that damage cells. Vitamin E is important in protecting body fat stores, blood cholesterol, lipid cell membranes and dietary fats from damaging oxidation. The more fats in your diet ­ especially healthy ones derived from olive oil and oily fish, the more vitamin E you need.

Vitamin E also has a strengthening effect on muscle fibres and is an important component of semen (see vitamin E and semen).

• EC/UK RDA: 10 mg/day

• US RDA: 10 mg/day

• It is estimated that 98 per cent of adults obtain less than this.

• UK average dietary intake: 9.7 mg/day. Observed intakes vary from 3.5­19.5 mg.

• Many experts now believe a daily intake of at least 40 mg to 50 mg vitamin E is needed to provide adequate protection against free radical damage causing coronary heart disease and cancer. This means taking supplements ­ though they must be of natural source vitamin E (d-alpha-tocopherol), not synthetic dl-alphatocopherol which is less biologically potent.

• Some sports nutritionists recommend that athletes obtain as much as 400­2,000 mg vitamin E per day. Vitamin C is required to regenerate vitamin E once it has performed its antioxidant role, therefore adequate supplies of both vitamins are essential. Studies suggest that athletes who supplement with vitamin C and vitamin E show a 25 per cent reduction in soft tissue damage, with muscle and red blood cell membranes sustaining less oxidative damage from free radicals generated during exercise. Muscles also seem to recover and regenerate more quickly following exercise.

• Foods rich in vitamin E include:

vegetable oils ­ of which wheatgerm oil is the richest

avocados

margarine

eggs

butter

wholemeal cereals

seeds

nuts

seafood

broccoli.