At first glance it would appear that most men not taking supplements are obtaining RDAs of most vitamins except betacarotene and possibly the important antioxidant vitamin E.
But RDAs are not recommended amounts for each individual we all vary greatly in our needs, according to our metabolic rate, our diet and the amount of exercise we take. Athletes usually need higher vitamin intakes than these.
RDAs are designed solely to compare populations and ensure that, in general, people are getting enough of the nutrients we all need. Athletes will need more of many of these vitamins, merely because they are making more demands on their metabolism the reactions for which vitamins are essential.
The other important point is that an average is only an average: half of the population will be getting more than the average intakes found in the government survey quoted above, and half will be getting less. For example, although the average vitamin C intake is 64.8 mg per day, the observed intake range is wide, with some men only obtaining 20 mg/day while others get as much as 170 mg/day from their diet.
It is estimated that 60 per cent of the British adult population are not getting the recommended amounts of vitamin C (60 mg/day) from their diet.
Vitamin A
Preformed vitamin A is only found in animal products. It is fat soluble, stored in the liver and most of us have enough stores to last at least one year.
Vitamin A is essential for vision, healthy moist eyes, sexual reproduction, the integrity of cell membranes and for normal growth and development.
• EC/UK RDA for adult males: 800 mcg (micrograms) of Vitamin A per day.
• US Recommended Daily Allowance (RDA): 1,000 mcg per day.
• There is no evidence that athletes need more than this amount.
• Most men in the Western world already have a vitamin A intake greater than this.
• Average dietary intake for British males: 1,186 mcg/day. Observed intakes range from 1906,560 mcg from food sources.
• Foods rich in vitamin A include:
• kidneys
• eggs
• milk
• cheese
• yoghurt
• butter
• oily fish.
• Margarine sold in the UK is also fortified with vitamin A by law.
• On average, men obtain 14 per cent of dietary preformed vitamin A from milk and milk products, 14 per cent from fat spreads, 6 per cent from cereal products, 4 per cent from eggs and egg products and a massive 55 per cent from liver products.
• Too much vitamin A is poisonous, causing symptoms of nausea, headache, visual disturbances, skin sloughing, coma and even death. It is important not to take supplements containing high doses of vitamin A. It is much safer to obtain your requirements in the form of the pro-vitamin, betacarotene.
Betacarotene
Various vitamin A-like compounds (carotenoids) are found in vegetables. Unlike vitamin A, these are water soluble and cannot build up in the body to cause harm, as whatever the body does not need is flushed out through the kidneys.
The most important carotenoid, betacarotene, consists of two molecules of vitamin A joined together. When body stores of vitamin A are low, some molecules of betacarotene are split to yield vitamin A. Zinc is essential for this reaction, so if zinc levels are low, there may be an associated deficiency of vitamin A.
When vitamin A stores are high, betacarotene stays as it is and has its own important functions in protecting against disease. It is a powerful antioxidant, helping to overcome the damage to cells caused by free radicals (see Chapter 21) and protects the male sperm.
• EC/UK RDA: none.
• US recommended intake (as suggested by the US National Cancer Institute): a minimum of 6 mg per day to reduce the risk of cancer.
• Research in the US on 22,000 male doctors has also shown that men with the highest intake of betacarotene reduced their risk of coronary heart disease by as much as 25 per cent.
• UK average dietary intake: 2.4 mg/day. This is way below NCI recommendations, although observed intakes range from 0.27.5 mg from food sources.
• Foods rich in betacarotene include:
• dark green leafy vegetables (e.g. spinach, broccoli)
• yellow-orange fruit (e.g. carrots, apricots, mangoes, red and yellow peppers and sweet potatoes).
• On average, men obtain 69 per cent of dietary betacarotene from vegetables and 13 per cent from meat and meat products, with the remaining amounts coming from cereal products, fruits, nuts and fat spreads.
Vitamin B1 (Thiamin)
Thiamin is needed for the production of energy from carbo-hydrate and for the synthesis of some amino acids. It also
plays a role in healthy nerve conduction. Athletes in training therefore need more of this vitamin than the average sedentary male to convert blood sugar into biological energy, and for the maintenance of healthy muscles.
Thiamin is water soluble and is not stored to any great extent in the body. An adequate daily supply is essential to burn the increased amounts of carbohydrate that athletes eat. Drinking large amounts of coffee or tea destroys this vitamin.
• EC/UK RDA: 1.4 mg/day
• US RDA: 1.5 mg/day
• UK average dietary intake: 1.7 mg/day. Observed intakes range from 0.82.9 mg from food sources.
Some sports experts advise athletes in training (on a high carbohydrate diet) to get as much as 50200 mg thiamin per day to maintain acceptable levels of this vitamin. There is no evidence that excess thiamin is toxic.
• Foods rich in vitamin B1 include:
wheat germ
wholegrain products
oatmeal
yeast extract
brown rice
meats
seafood
pulses
nuts.
• Highly milled grains (e.g. polished white rice) and those that have been in storage for any length of time will lose their thiamin content.
• On average, men get 38 per cent of dietary thiamin from cereal products, 26 per cent from vegetables (mainly potatoes), 19 per cent from meats and 8 per cent from milk products.
Vitamin B2 (Riboflavin)
Riboflavin is another water-soluble vitamin essential for smooth metabolic functioning. It is known as 'the exerciser's friend' as it is involved in the production of the energy within mitochondria.
It is also involved in the metabolism of carbohydrate, fatty acids and protein. As such, an adequate supply is essential for athletes, who require more than sedentary men. If riboflavin is in short supply, oxygen consumption goes down, thereby impairing performance.
• EC/UK RDA: 1.6 mg/day.
• US RDA: 1.7 mg/day.
Those who exercise moderately probably need a total of at least 22.5 mg riboflavin per day. Some sports nutritionists recommend intakes of 25 mg to 200 mg for athletes in full training, in order to maintain personal performance. There is no evidence that excess riboflavin will boost performance, or that it is toxic.
• UK average dietary intake: 2.1 mg/day. Observed intakes vary from 13.6 mg from food sources.
• Foods rich in riboflavin include:
liver
milk
cheese
yoghurt
yeast extract
eggs
wheat bran
green leafy vegetables
mushrooms
fruits
bread
cereals
meats.
• On average, men get 26 per cent of dietary riboflavin from milk and milk products (especially cheese), 22 per cent from meat and meat products and 21 per cent from cereals. 8 per cent of intake comes from beer.
Vitamin B3 (Niacin; niacinamide; nicotinamide; nicotinic acid)
Niacin is another water-soluble vitamin that plays an important role in the formation of metabolic enzymes and energy production. It is essential for producing energy from glycogen, for the oxidation of fatty acids and for tissue respiration. As such, athletes require more niacin than sedentary men.
It comes in several forms and can also be synthesized in the body from the essential amino acid, tryptophan.
• EC/UK RDA: 18 mg/day.
• US National Research Council recommended intake: 19 mg/day.
Some sports nutritionists recommend that athletes in training need as much as 30100 mg per day (mostly in the form of nicotinamide) to maintain adequate levels. Don't take more than this unless under medical supervision, and stick to nicotinamide which does not cause flushing. Intakes of over 30 mg niacin and intakes above 100 mg nicotinic acid dilate blood vessels, leading to skin redness, burning, tingling and itching the so-called 'niacin flush'. This is not dangerous in itself, but a few people also suffer nausea, headache, muscle cramps and diarrhoea. Lowered blood pressure and pulse may also induce feelings of faintness.
Doses above 500 mg niacin equivalents per day are toxic and can lead to liver damage.
• UK average dietary intake: 40 mg/day. Observed intakes vary from 2162 mg from food sources.
• Foods rich in vitamin B3 include:
lean meat
fish
poultry
yeast extract
peanuts
bran
beans
milk
whole grains.
• On average, men get 34 per cent of dietary niacin from meat and meat products, 27 per cent from cereals, 10 per cent from vegetables and 9 per cent from milk and milk products.
Theories that megadoses of niacin will boost athletic perform-ance are untrue. There was an initial flurry of excitement at findings that high intakes of niacin (310 g daily!) helped to mobilize and burn glycogen more quickly as a fuel.
Unfortunately, this effect also blocks the use of fatty acids as a fuel, leading to rapid glycogen depletion. Performance is therefore actually impaired.
Sixty mg of the amino acid tryptophan is equivalent to 1 mg of preformed dietary niacin. Niacin equivalents are estimated by adding preformed niacin intake plus one sixtieth of tryptophan intake.
Interestingly, it is estimated that intakes of tryptophan among sedentary Western adults is more than adequate to meet niacin needs even if no preformed niacin were available in the diet.
Vitamin B5 (Pantothenic acid)
Pantothenic acid is also a water-soluble vitamin essential for many energy-yielding metabolic reactions involving carbohydrates, fats and protein. It is an important component of Co-enzyme Q (an enzyme-helping factor responsible for many metabolic reactions), and is also required for the synthesis of glucose and fatty acids within the body.
• EC/UK RDA: 6 mg/day.
• US RDA: 6 mg/day.
• UK average dietary intake for men: 6.2 mg/day. Observed intakes range from 310 mg from food sources.
Active athletes use up to four times the daily energy of sedentary men and therefore require a higher intake of pantothenic acid. Some sports nutritionists suggest that athletes in training obtain 20200 mg pantothenic acid per day to reduce the build-up of lactic acid and maximize oxygen consumption. There is no evidence that excess is toxic.
Claims that pantothenic acid can boost athletic performance are interesting. In one study, highly conditioned long-distance runners were given 1 g of pantothenic acid daily for 14 days. Another group was given an inactive placebo and their performance (using a treadmill) was compared to that of the first group. No differences were noted.
In another trial, however, long-distance runners were given 2 g pantothenic acid daily for two weeks and another group received a placebo. Differences were found here. Those receiving megadoses of pantothenic acid experienced a 17 per cent reduction in lactic acid build-up and consumed 8 per cent less oxygen to perform an equivalent amount of work.
In view of the conflicting evidence, more research is awaited before definite claims are made.
Pantothenic acid derives its name from the Greek meaning found 'on all quarters'. It is widely distributed in nature and found in almost every food source, especially meat, eggs and whole-grain cereals. Perhaps the richest source is royal jelly.
