Nutrition for Cyclists E-Book

Jane Griffin

• Herausgeber: Crowood
• Kategorie: Lebensstil
• Sprache: Englisch

Seitenzahl: 233

Veröffentlichungsjahr: 2014

Beschreibung

Nutrition for Cyclists is essential reading for all keen riders who want to learn about what, when and how much to eat and drink to improve their performance. This practical book shows cyclists how to design the right diet that will allow them to incorporate a rigorous training regime into a busy lifestyle. With over 30 years' experience of working with sportsmen and women at the highest levels, Jane Griffin explains the background science behind her dietary advice and addresses the day-to-day concerns of cycling enthusiasts. Topics include: the energy requirements of the cyclist; effective meal planning for training and competition; how to stay hydrated and how to rehydrate efficiently; eating to aid recovery from illness or injury; supplements and Ergogenic Aids; how to lose weight and maintain performance and finally, special advice for younger, older, female and vegetarian cyclists."Diet and nutrition are as key a part of cycling as the pedals or chain." Nigel Mitchell, Head of Nutrition British Cycling/Team Sky. Illustrated with 40 colour images and diagrams.

Leseprobe

NUTRITION

FOR

CYCLISTS

JANE GRIFFIN

First published in 2014 by

The Crowood Press Ltd

Ramsbury, Marlborough

Wiltshire SN8 2HR

This e-book first published in 2014

www.crowood.com

© Jane Griffin 2014

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

ISBN 978 1 84797 843 1

Acknowledgements

To my husband Chris for his love, support, encouragement and wise words – not to mention the endless mugs of tea and coffee and the evening meals he produced while I shut myself away in my study.

A very big thank-you must go to Nigel Mitchell, the Head of Nutrition at British Cycling/Team Sky. On a trip to the Velodrome in Manchester, we sat watching the top cyclists in the country train as Nigel told me about the Tour de France and the nutritional requirements generally of elite cyclists, both in training and in races.

Another thank-you goes to the Dairy Council for giving me permission to reproduce the diet plan which appeared in their publication Nutrition for Cyclists – the Milk Race.

CONTENTS

Introduction

1   Nutrition Basics

2   The Cycling Body

3   Training Diet

4   Training Fluids

5   Competition

6   Supplements and Ergogenic Aids

7   The Travelling Cyclist

8   Special Considerations

9   Injuries and Illnesses

Appendices

References

Index

INTRODUCTION

In the 2014 Annual Report of the Chief Medical Officer, Professor Dame Sally Davies said that while many people think cycling is dangerous because we hear about deaths on the road, cycling is usually a safe and healthy thing to do but the benefits don’t make the headlines. The British Medical Journal published an article in February 2014 entitled ‘London bike hire has positive impact on health’. The researchers from the medical school in Cambridge investigated to see if the physical activity of cycling outweighed the risks of road traffic accidents, collisions and inhalation of polluted air. The results showed the greatest benefit was to older users (over 29) and particularly to men but also women.

Cycling, rather like running, is a simple sport! A runner needs a pair of decent running shoes and a water bottle; a cyclist needs a bike and a water bottle. Those are the basics; of course there can be many more ‘add-ons’, such as special clothing, shoes and gadgets, but it is not a complicated sport. A cyclist can go out alone, or with the family, or cycle with a friend, a neighbour or a cycling club. A cyclist can go out for a long ride or just a short ride.

As a sport, cycling has blossomed in recent years, no doubt in part because of the success of British Cycling at events such as the Olympics and the Tour de France. Long may this enthusiasm for cycling continue!

CHAPTER 1

NUTRITION BASICS

Cyclists rely on what they eat and drink every day to supply all their energy and nutrient requirements. The one exception to this is vitamin D, which the body can make by the action of sunlight on bare skin. The need for a special diet is therefore very small for most people and cyclists who go out on their bikes regularly should certainly be making sufficient vitamin D – as long as enough skin is exposed! So what does the diet have to provide to keep the cycling body fit, healthy and stored with enough energy to meet each day’s requirements?

The body needs a regular supply of water, energy (calories), carbohydrate, fat and protein, vitamins and minerals. Requirements for health and well-being can easily be met by a varied diet – in other words, one that contains lots of different foods and drinks. For most people, problems arise not so much because of a scarcity of food (as happens in times of famine through crop failure or over-population) but rather through intakes that are habitually greater than requirements. An advantage of taking part in regular exercise such as cycling means that cyclists need to eat and enjoy more food than sedentary individuals, while still being able to maintain a healthy weight for their sport. However, this does not mean they have an open invitation to eat anything (fast foods, for example) or to eat as much as possible at every meal. Achieving the right quality, quantity and variety of food and fluids consumed on a daily basis is the nutritional key to remaining healthy and maximizing cycling performance. Too little and the body could be likened to a car with an empty petrol tank: in other words, it’s not going anywhere very fast! Regularly consuming more than the body needs leads to an increase in body-weight (as body fat) and a much greater effort will be required to maintain cycling intensity and/or duration. If daily food choices do not meet daily requirements for energy and nutrients, performance will suffer, the risk of infections and injuries will increase, and there may even be long-term health implications. Not only do nutrients have different functions in the body, but the type and quantity of nutrients in what we eat varies from food to food. Understanding what energy and nutrients do in the body, and which foods are good sources of particular nutrients, provides the foundations to build the best possible diet to maximize performance both in training and races. Not only that, it will help in keeping the body fit and healthy. On the practical side, the diet must fit into a cyclist’s lifestyle and daily schedule – and just as importantly it must be enjoyable. It can be very hard for a cyclist to meet the increased energy and nutrient requirements of cycling when training hard and regularly, especially on top of holding down a job or studying and having some social and family life too. This can be particularly difficult if food consumed on a daily basis is boring and repetitive, and may not be what the body needs nutritionally in terms of quality and quantity.

Nutrients and their main functions

Food is made up of carbohydrate, fat, protein, vitamins, minerals and water. In some foods, particularly fruit and vegetables, a very large proportion is water, whereas in others, such as oils and fats, the water content is minimal. The amounts and indeed the presence of the different vitamins and minerals can vary considerably between foods, too. Health professionals spend a lot of time encouraging people to eat a diet that contains a wide variety of different foods to help ensure that the requirements for all the essential nutrients are being met on a regular basis. Carbohydrate and fat are the major sources of energy or fuel for the human body. Protein, however, has a unique function. It provides the material for growth and repair of the body. Vitamins and minerals are essential nutrients and the body depends on the diet to supply them, with the exception of vitamin D, which can be made by the action of sunlight on the skin (as already mentioned). However, in some parts of the world the amount of daily sunlight can be very limited, with a risk that some people living in these places might become vitamin D deficient. The vast majority of vitamins and minerals are needed in very small amounts, yet they have vital and very varied roles to play in maintaining health and well-being. Vitamins make up quite a diverse group of substances that are important in the regulation of different chemical processes constantly going on in the body. They are not a source of energy, though many vitamins are involved in the release of energy from food. Minerals, rather like vitamins, also have many different functions. They help in controlling the composition of bodily fluids and are important constituents of teeth and bones. They are also essential components of enzymes, which act like biological catalysts regulating biochemical reactions, and also of proteins, such as the oxygen-carrying haemoglobin.

Energy

The energy needed by the body comes solely from the diet – in other words, the food and fluids we consume on a regular, daily basis. Our bodies digest, absorb and metabolize what we eat and drink, releasing energy for the body to use. As the body’s energy requirements increase, more food and fluids will need to be consumed to meet these requirements. Active individuals will therefore have greater requirements than sedentary individuals (in some cases considerably greater). Taking part in a sport such as cycling not only helps the body keep healthy, but also means that cyclists are able to enjoy their food without constantly worrying about eating more than their body needs with the inevitable gain in weight. However, it is not an invitation to eat to excess or ‘fit to bursting’!

The energy value of food

1g protein → 4kcals

1g fat → 9kcals

1g carbohydrate → 3.75kcals (on food labels a factor of 4kcal is used)

1g alcohol → 7kcals

1g water → 0kcals

These nutrients make up most of the weight of a food. Vitamins and minerals, though vitally important in the diet, account for very little of the actual weight of the food. Fruit and vegetables contain a large percentage of water and as a result have relatively fewer calories than fatty foods such as butter, margarine, lard and oils, which all have a low water content and therefore a much higher calorie count on a weight basis. It is worth mentioning here that water does not have a calorie value – it really does contain no calories, whether it is out of a tap or out of a bottle! The vast majority of foods are a mixture of nutrients and the energy value of any particular food will be the sum of the energy value of each nutrient (carbohydrate, fat, protein and alcohol).

Carbohydrate

Carbohydrates are found in the diet either as simple carbohydrates (sugars) or as starches. Most dietary carbohydrate is plant in origin. The only exception is lactose, the sugar that occurs in milk whether it is from a human, cow, goat or other mammal. Fruits and fruit juices, milk and milk products, honey and sugar are the main sources of simple carbohydrates in our diet. They can be identified easily by their sweet taste. Simple carbohydrates have often been vilified. The famous nutritionist Professor John Yudkin wrote a book, first published in 1972, entitled Pure, White and Deadly. He was one of the first scientists to claim that sugar was a major cause of obesity and heart disease. (He was also this author’s professor of nutrition at London University.) Apart from sugar, there are many other factors that need to be considered when determining the causes of these health problems, including intakes of fat, saturated fat, salt and alcohol, inactivity and smoking. It is not the purpose of this book to debate this topic but it is perhaps pertinent to remember that sugar grows naturally as sugar cane and sugar beet and that it also occurs naturally in fruits and certain root vegetables, including carrots. Sugar (or sucrose, to give the correct terminology) is made up of two simple sugars, glucose and fructose. There is no nutritional difference between white and brown sugar. It is all a matter of taste and appearance. Simple carbohydrates are all characterized by their sweet taste. Starchy or complex carbohydrates are found in bread, pasta, rice, potatoes, breakfast cereals, pulses and sweetcorn.

Carbohydrates are the most important source of energy in the diet as they are the optimum energy source for exercising muscles, the brain and the central nervous system. Anyone who has tried to follow the one-time popular low-carbohydrate/high-protein diet will surely remember how tired, lethargic and irritable they were as their body became more and more carbohydrate depleted. The amount of carbohydrate that our bodies can store in the liver and muscles (known as liver or muscle glycogen) is limited. This helps to explain why sports dietitians and sports nutritionists put so much emphasis on foods that provide carbohydrate. (SeeChapter 3 for sources of carbohydrate.)

Dietary Fibre

Fibre was originally called roughage, which, according to the author’s dictionary, is ‘the coarse indigestible constituents of food which provide bulk to the diet and aid digestion’. It is now called non-starch polysaccharide (NSP) but most people still refer to it as dietary fibre, which is also the terminology or wording used on food labels. Fibre is a major component of plant cell walls. The key dietary contributors of fibre are therefore fruits, vegetables and cereals. Dietary fibre can be soluble or insoluble, and it is the solubility or lack of it that determines its function. People are encouraged to eat more insoluble fibre because of its ability to help keep the lower part of the digestive system (the bowels) functioning in a healthy and regular manner. It does this by absorbing water, which makes the gut contents heavier, which in turn speeds up the movement down the gut. This can help in relieving constipation and other bowel disorders. The main contributors of insoluble fibre in the diet are cereals such as wheat, maize and rice.

Soluble fibre occurs particularly in oats, legumes (peas and beans), leafy vegetables and some fruits, most notably apples. It has quite different effects in the body from insoluble fibre, probably playing a part in helping to lower blood cholesterol levels and slow down the rate of post-prandial absorption of glucose (particularly important in some types of diabetes). Healthy eating messages encourage the inclusion of dietary fibre in the diet of the general population. As carbohydrate figures strongly in the dietary recommendations for cyclists, it is likely that the vast majority of cyclists consume sufficient dietary fibre without the need to choose high-fibre sources. Cyclists who actually prefer high-fibre foods from an organoleptic point of view (i.e. they like the taste/texture better), will need to be careful about how much high-fibre food they consume on a regular basis and should certainly take particular care not to overload with high-fibre foods on race days! (SeeChapter 9 for the reasons why.)

Fat

Fat is an essential nutrient and an important source of energy. Many people eat excessive amounts of high-fat foods and would benefit from reducing their intake. However, fat should never be avoided totally. Apart from supplying the body with energy, fat also supplies the essential fatty acids of the omega-3 and omega-6 families. These are termed ‘essential’ because the human body is unable to make them and must rely on supplies provided by the diet. Other functions performed by fat include insulating and protecting the internal organs in the body, acting as carriers for fat soluble vitamins and antioxidants, and playing a part in the formation of certain hormones. Hormones are chemicals that are made in one part of the body and have an effect in another part of the body. They act as chemical messengers to regulate specific body functions. For example, insulin is a hormone made in the pancreas, specifically in the beta cells of the Islets of Langerhans (remember that for a quiz supper question!), but it has the job of controlling the concentration of glucose in the blood.

Fat plays another important part, particularly in the enjoyment of what we eat. Many flavours, smells and textures are linked to the fats in food and without them our food would taste remarkably bland. It may make our food more enjoyable, but an excessive amount of fat in the diet is not to be recommended as it is considered to be one of the risk factors linked to the development of chronic diseases, particularly obesity and heart disease. Reducing fat intake is not necessarily a simple thing to achieve as the amount of fat in food is not always obvious to the consumer; some is very visible, such as butter and margarine, while some is hidden, as in eggs and homogenized milk.

Sources of fat

Visible fat:Invisible fat:Butter, margarine, gheeVery lean cuts of meatOils, lard, suet, drippingCheeseHydrogenated fats and vegetable shorteningWhole milk (full fat)Cream– Semi-skimmed milkFat on meat, poultry skin– Skimmed milkOily fishEggsMeat products: pies, pasties, sausages, burgers,pâté, salami, tinned meatsChips, crisps and roast potatoesNuts, olives, avocado pearsFried food and pastrySome cakes and biscuitsCreamy puddings and cheesecakeMayonnaise, salad cream, creamy saucesPeanut butterChocolate, toffee and fudge

Protein

Protein performs vital structural functions in the body and can be found in muscle, bone, cartilage, tendons, ligaments, skin and hair. It is needed for growth and development, and has an on-going role in rebuilding, repairing and maintaining vital body tissues. Enzymes are proteins that can act as catalysts, increasing the velocity or speed of biochemical reactions taking place in the body. Some hormones are proteinous in nature. Insulin, which is responsible for preventing excessive rises in blood glucose levels, is an example of a proteinous hormone. Other proteins have important roles to play in the immune system, where they help to fight off infections, while others act as transporters of fats, minerals and oxygen. In some situations protein can be used as a source of energy, but with so many unique functions this is usually a last resort. Protein, unlike fat (and to a certain extent carbohydrate), cannot be stored in the body. If more protein is eaten than is needed, part of the protein molecule is broken down and excreted from the body in urine and the rest is used as an immediate source of energy or it can be converted into fat and stored.

Poultry is a good source of protein, but the skin is also a source of fat

Eggs have a high protein content and high biological value.

Amino Acids

Amino acids are the building blocks of protein, and all the various proteins needed by the human body can be made from just twenty different amino acids. Essential amino acids cannot be made by the body and must therefore be supplied by the diet. Non-essential amino acids can be made from other amino acids.

Classification of amino acids

Essential amino acids:

Histidine (only in infants)

Isoleucine

Leucine

Lysine

Methionine

Phenylalanine

Threonine

Tryptophan

Valine

Non-essential amino acids:

Alanine

Arginine

Asparagine

Aspartic acid

Cysteine/cystine

Glutamic acid

Glutamine

Glycine

Proline

Serine

Tyrosine

Animal protein versus vegetable protein

The amount of protein in a particular food is obviously important, particularly when a cyclist is aiming for a specific protein intake. However, the quality of the protein must also be taken into account, so it is important to have some knowledge about which amino acids are present in a protein and in what amounts, as well as the overall quantity of protein. Animal sources of protein such as meat, fish, eggs, milk and cheese have high protein contents with a high biological value. Pulses (soya bean, kidney beans, chickpeas, lentils and peanuts) have very high protein contents and a high (in the case of soya) or medium biological value. Beans and peas belong to a food group called legumes; contrary to popular belief, peanuts fall into this category too. Peanuts grow underground and hence are also called ground nuts. Cereals (wheat, rice, barley, maize and oats) have medium protein contents and, with one exception, a low biological value; the exception is rice, which has a medium value. Nuts (walnuts, brazil nuts, hazelnuts, cashews, almonds, pine nuts and pistachios) have high protein contents but their biological value is on the low side. Starchy roots (potato, cassava, yam and sweet potato) are low in protein and also have a low or negligible biological value. Vegetables and fruits are low in protein; in fact they are not really thought of as a source of protein – they have far more important roles to play in the daily diet.

Sources of protein

Animal sources:

Meat

Offal (kidney, liver, heart, tongue, tripe)

Poultry

Fish (white, oily and shellfish)

Eggs

Milk, cheese, yoghurt

Vegetable sources:

Beans, peas and lentils

Nuts and seeds

Quorn and tofu

Soya beans, soya milk

Textured vegetable protein

Bread, potatoes, rice, pasta, cereals

Opt for wholemeal bread where possible as it is a good source of the B complex vitamins.

Excessive protein intakes

A diet that regularly contains unnecessarily high amounts of protein will place an increased workload on the kidneys as they have to excrete what the body does not need. In healthy people this may not present any problems, but it may do for some cyclists, particularly those who are not very good at replacing fluid lost through sweating (seeChapter 4).

Vitamins

Vitamins are complex organic substances that are needed in very small amounts but nevertheless have vital and quite varied functions in the body. With the exception of vitamin D, which can be made by the action of sunlight (UV light) on exposed skin, the diet must provide all these vitamins. Vitamin deficiencies are rare in the UK although they still occur in some parts of the world where diets are very limited, either because of severe shortages of food or through a lack of variety in the diet. Vitamins A, D, E and K are fat-soluble vitamins that can be stored in the body. Vitamin C and the B complex vitamins are water soluble and are not stored in the body. Water soluble vitamins consumed in excess of the body’s requirements are usually excreted by the kidneys in the urine.

Vitamin A

Major food sources:

Vitamin A is found in animal foods as retinol. Plant foods contain beta-carotene, the precursor of vitamin A. The richest sources of vitamin A are fish liver oils (cod liver oil) and animal liver (lamb, calf and pig). Good sources of vitamin A include oily fish (mackerel, herring, tuna, sardines and salmon), egg yolks, full fat milk, butter, cheese and fortified margarine. Good sources of beta-carotene are fruit and vegetables, especially orange ones (carrots, apricots), dark green ones (spinach, watercress and broccoli) and red ones (tomatoes and red peppers).

Main functions:

Essential for healthy skin.

Maintains healthy mucous membranes in the throat and nose.

Protects against poor vision in dim light.

Antioxidant properties.

Deficiency:

Very rare in the UK but in Third World Countries vitamin A deficiency is a major cause of blindness.

Requirements:

Reference Nutrient Intake (RNI) for adult women is 600µg per day and for adult men is 700µg per day.

Excessive intake:

Regular intake of retinol should not exceed 7,500µg for adult women, 9,000µg for adult men and 3,300µg for pregnant women. Women who are or might become pregnant are advised by the Department of Health not to take vitamin A supplements or eat liver, as excessive amounts can be toxic and dangerous to the unborn child.

Vitamin B1 (thiamin)

Major food sources:

Cereal products such as breakfast cereals, bread, pasta and rice, lean pork and peas, beans and lentils.

Main functions:

Release of energy from carbohydrate.

For normal functioning of nerves, brain and muscles.

Deficiency:

Very rare in the UK but causes beri-beri, which affects the heart and nervous system.

Requirements:

RNI is 1.0mg per day for adult men and 0.8mg per day for adult women. (Dependent on the energy content of the diet, an RNI is set at 0.4mg per 1,000kcals for most groups of people.)

Excessive intake:

Chronic intake in excess of 3g per day is toxic in adults.

Vitamin B2 (riboflavin)

Major food sources:

Milk, egg yolks, liver, kidneys, cheese, wholemeal bread and cereals, green vegetables. Sensitive to light.

Main functions:

Release of energy from carbohydrate, fat and protein.

Deficiency:

Severe deficiency is unlikely in UK but causes sores in the corners of the mouth.

Requirements:

RNI for adult men is 1.3mg per day and for adult women 1.1mg per day.

Excessive intake:

Absorption of riboflavin in the intestine is limited so toxic effects are unlikely.

Niacin (nicotinic acid, nicotinamide, vitamin B3)

Major food sources:

Meat, poultry, fortified breakfast cereals, white flour and bread, yeast extracts.

Main functions:

Release of energy from protein, fat and carbohydrate.

Deficiency:

Rare.

Requirements:

RNI for adult men is 17mg per day and for adult women 13mg per day.

Excessive intake:

Very high intake in the region of 3–6g per day may cause liver damage.

Vitamin B6 (pyridoxine)

Major food sources:

Meat, particularly beef and poultry, fish, wholemeal bread and fortified breakfast cereals.

Main functions:

Needed for protein metabolism, central nervous system functioning, haemoglobin production and antibody formation.

Deficiency:

Deficiency signs are rare.

Requirements:

RNI for adult men is 1.4mg per day and for adult women 1.2mg per day.

Excessive intake:

High intake has been associated with impaired function of sensory nerves. The amounts involved have varied from 50mg per day to 2–7g per day.

Vitamin B12 (cyanocobalamin)

Major food sources:

Found only in food of animal origin (liver, kidney, meat, oily fish, milk, cheese and eggs). Some breakfast cereals are fortified with vitamin B12. Some vegetarian foods are also fortified, for example soya protein, soya milks, yeast extract.

Main functions:

Red blood cell formation, maintenance of nervous system and protein metabolism.

Deficiency:

Pernicious anaemia (blood disorder).

Requirements:

RNI for adult men and women is 1.5µg per day.

Excessive intake:

Excess is excreted in the urine and therefore is not dangerous.

Folic acid (folates)

Major food sources:

Liver, kidney, green leafy vegetables, wholegrain cereals, fortified breakfast cereals and breads, eggs, pulses, bananas and orange juice.

Main functions:

Red and white blood cell formation in bone marrow.

Essential for growth.

Protection against neural tube defects (spina bifida) pre-conceptually and in early pregnancy.

Deficiency:

Megaloblastic anaemia (blood disorder).

Requirements:

RNI for adults is 200µg per day. Women who might become pregnant and women during the first twelve weeks of pregnancy are recommended to take an extra 400µg per day.

Excessive intake:

Dangers of toxicity are very low.

Biotin and Pantothenic acid

Major food sources:

Widespread in food.

Main functions:

Release of energy from fats, carbohydrates and protein.

Deficiency:

Unlikely.

Requirements:

None set.

Excessive intake:

No danger.

Vitamin C

Major food sources:

Fruit and vegetables, especially blackcurrants, strawberries and citrus fruit, raw peppers, tomatoes and green leafy vegetables, and potatoes because of the amount eaten.

Main functions:

For healthy skin, blood vessels, gums and teeth, wound healing, iron absorption and formation of antibodies. It is an important antioxidant.

Deficiency:

Serious deficiency causes scurvy. Mild deficiency leads to tiredness, bleeding gums, delayed wound healing and lowered resistance to infection.

Requirements:

RNI for adults is 40mg per day.

Excessive intake:

Intakes at levels of twenty times the RNI or more have been associated with diarrhoea and increased risk of oxalate stones in the kidney.

Vitamin D (cholecalciferol)

Major food sources:

Fortified margarines and spreads, fortified breakfast cereals, oily fish, egg yolks, full fat milk and dairy products. The main source of vitamin D is the action of sunlight (UV light) on the skin.

Main function:

Absorption of calcium and its utilization in the body, particularly the mineralization of bones and teeth.

Deficiency:

Loss of calcium from the bones causes rickets in young children and osteomalacia, particularly in women of child-bearing age.

Requirements:

No dietary source is needed for adults provided that their skin is exposed to sunlight (RNI for adults aged 65 and over is 10µg per day).

Excessive intake:

Toxicity is rare in adults.

Vitamin E

Major food sources:

Vegetable oils, seeds, nuts (especially peanuts), wheat germ, wholemeal bread and cereals, green plants, milk and milk products, and egg yolks.

Main functions:

Powerful antioxidant, protecting body tissues against free radical damage.

Deficiency:

None except in very exceptional circumstances.

Requirements:

No RNI set; 4mg per day for adult men and 3mg per day for adult women considered adequate.

Excessive intake:

Toxicity extremely rare.

Vitamin K

Major food sources:

Dark green leafy vegetables, margarines and vegetable oils, milk and liver. Vitamin K can also be synthesized by bacteria in the gut.

Main functions:

Blood clotting.

Deficiency:

Rare in adults.

Requirements:

No RNI set, but 1µg per kg per day is considered both safe and adequate.

Excessive intake:

Natural K vitamins seem free from toxic side-effects, even at up to a hundred times the safe intake. Synthetic forms may not have such a wide margin of safety.

Minerals