Cancer – Can Your Diet Make the Difference?

Firstly, can it really be said with confidence that if you eat much less, or much more, of a particular foodstuff - or combination of foodstuffs - you will become immune or less at risk to this or that cancer? To begin with, it has been proved beyond doubt that cancer can be prevented in experimental animals through dietary changes. In particular, reduced energy (kilojoule) and fat intakes and increased consumption of fibre- rich foods and certain vitamins have been found to inhibit the development of cancer. The question is, can these findings be appliedto human beings?

Here there are two very important questions: Firstly, to what extent is there a link between human diet and cancer, and secondly, how drastic are the changes we have to make to our eating patterns in order to bring about a significant drop in cancer development?

The first question is possibly easier to answer than the second. Researchers are now convinced that, in dietary terms, humans share the same cancer risks as animals. Simply put, these are:

• eating too much food in general and too much fat in particular
• not eating enough of the fibre contained in grains, legumes (beans, peas, lentils), fruit and vegetables
• low intakes of certain vitamins

The fat, vitamin and fibre factors

A high fat intake leads to a high concentration of faecal bile acids which can, under certain circumstances, act as carcinogens (cancer- producing substances). A low fibre intake results in a high faecal pH value, which favours the development of carcinogens; it also causes waste to take longer to move through the bowel, allowing time for cancer-causing substances to develop and take effect. On the other hand, a low intake of certain vitamins has a negative effect on the mechanisms which combat damaging reactions in the body's cells.

High fat diets - especially those high in saturated fats - have been linked to cancers of the breast, prostate and colon-rectum and low fibre diets to the latter in particular. A diet low in vitamin C is associated with gastric cancer, while one that is deficient in vitamin A seems to create favourable conditions for prostate cancer; a lack of vitamin D is linked to cancer of the colon. The mechanisms involved in all these processes are far from clear and much research still has to be done. (See also The Cabbage Patch Diet on page 187.)

The challenge to change

Authorities on cancer such as the US National Cancer Institute, the 1988 US Surgeon-General's Report and the 1989 Report of the UK COMA (Committee on Medical Aspects of Food Policy) have laid down guidelines for dietary changes which they regard as vital in the fight against cancer. Firstly, they maintain that fat should supply only 25-30% - instead of the present 40⁰/a - of our total food intake. In effect, this reduction by a third or so would bring our fat consumption to the level of the poorest people in the big cities in the 1920s! No fall in fat intake has occurred recently in Western populations.

For a marked fall, there would have to be a big increase in the intake of carbohydrate, or starchy, foods. But as mentioned above, our bread consumption is low - 120-150g or 3 to 4 slices daily - and possibly decreasing. Why has it fallen? Firstly, there has been a marked increase in the consumption of more 'palatable' foods such as dairy produce, meat, fish and eggs and secondly, the modern era's obsession with slimness has led to the (erroneous) belief that bread is specially fattening. It is invariably one of the first foods to be restricted or cut out totally in any attempts at weight loss.

In practical terms, to reduce our fat intake to the recommended levels, the average person would have to eat a good 50% less of all visible fat - butter, margarine, spreads and obvious fat on meat - than at present. The realization that changes in this area must be large, not trivial, has been underlined by recent studies which show that in the case of breast cancer, only a very low fat intake which supplies as little as 25% of energy (50-60g fat daily), is likely to give protection.

What about fibre? The experts recommend that it be increased from the present 10-15g to 25-30g or more daily, through a higher consumption of fibre-containing foods, cereal products (wholewheat bread, brown rice and unrefined breakfast cereals), legumes, vegetables and fruit. This means adopting a diet similar to that of strict vegetarians. In the USA, surveys show that only half of the population eat one serving of fruit and one serving of 'garden' vegetables on any one day - yet four or five helpings arerecommended. The fact of the matter is that in most countries, there have been no significant increases in the amounts of plant foods eaten daily.

The picture is much the same when it comes to intakes of vitamins and mineral salts. Admittedly, pill manufacturers are doing a roaring trade, but as any doctor will tell you, that is not the way to get your vitamins. Nature has provided us with an abundance of fruit and vegetables which, apart from being excellent sources of vitamins and fibre, are a good deal lighter on the pocket than the packaged variety. In addition, some vegetables have been found to be particularly effective in fighting diet-related cancers because of their high concentrations of certain vitamins.

Indifference - the biggest enemy? continue...

Colon cancer update

Some recent findings to do with the prevention of colon cancer (one of the most common cancers) are heartening. Studies on human beings have shown that including less fat and more fibre in one's dietprobably lessens the presence of `mutagens' (substances which can promote the development of cancer) in the bowel contents.

A recent four-year study in the USA also produced interesting results. The subjects of the research were a series of patients with 'familial adenomatous polyposis'. This refers to a segment of the population with bowel polyps which are particularly prone to become cancerous. (Polyps are growths with a pedicle or stem which usually develop on mucous membranes.) These patients were put on a high fibre diet (about 22g of fibre daily compared with the usual daily intake of about 12g), the extra fibre being provided by commercial bran cereal. In all the patients, a regression or shrinking of the polyps resulted - an outcome which was regarded as very promising by the US National Cancer Institute.

Also interesting is the fact that elderly blacks examined in the Department of Gastroenterology at Baragwanath Hospital, Soweto, showed no evidence of polyps; indeed their bowels had the appearance and elasticity of that of white teenagers! Among old rural blacks, colon cancer is extremely rare and even among urban dwellers, its occurrence is only a tenth of that found in elderly whites. The significance seems to be that the diets of these people are generallymuch higher in fibre and lower in fat than those of their white counterparts.

Eating to combat cancer - a day's sample menu**

* Breakfast: Cereals (such as All-Bran flakes or Weet-Bix), or oatmeal porridge, with milk and sugar

* Orange juice, a poached egg on brown (preferably wholewheat) toast and a couple of slices of tomato

Tea or coffee

* Lunch: 2 or 3 slices of brown or wholewheat bread with margarine,cottage cheese, salad (eg lettuce, celery, raw carrot), an apple or a banana

Tea or coffee

Dinner: Fish or chicken (not fried), brown rice, baked or newpotatoes, a green vegetable, baked beans, gem squash and a brown roll

Stewed or canned fruit (eg pineapple) and yoghurt

**This suggested menu provides about 30% of energy from fat and about 20-25g dietary fibre.

The alcohol/cancer link

Too much alcohol is a risk factor for the development of several cancers, especially of the liver, oesophagus, lung, pancreas and rectum. But here again, little notice has been taken of calls to cut down and levels of consumption are still rising, not only in many Western populations but in all Third World urban populations as well.

What is a reasonable or safe alcohol intake? For the majority of consumers there is no health problem, since it is considered that the majority of people who drink do so moderately and never experience any harmful effects. The crucial question is: What is a sensible limit? The liver burns up one standard drink (a half pint of beer, a glass ofwine, a measure of whisky) in an hour. With this in mind, the following safe allowances have been put forward:

For men, four to six standard drinks, two or three times a week. Or, at most, from 18 to 20 standard drinks weekly. For women, two or three standard drinks, two or three times a week or, at most, 9 to 13 standard drinks weekly.

These recommendations (endorsed by World Health 1985) were set out by the London Health Education Council in a booklet titled 'That's the Limit: a Guide to Sensible Drinking'. The reason why the limits for women are lower than for men is twofold: firstly, in men, water makes up 55-65°/o of body weight and in women, 45-55%, therefore alcohol is more diluted in men than in women; secondly, alcohol is potentially more noxious in women than in men.

Smoking and cancer

Smoking is believed to be responsible, directly or indirectly, for about a third of total cancers. It increases the risk of certain diet-related cancers such as breast cancer, but appears to have little influence with others, such as cancer of the prostate. In many Western populations there has been a major decrease in cigarette smoking among men, although far less so among women. In the USA, current frequencies are 32% for men, but 26% for women. Nowadays more young women than young men smoke, and today's female smoker is a heavier onethan yesterday's!

In Third World countries, tobacco use is rapidly increasing - in African populations, consumption has doubled in the last 10 years. So the dismal view is that all tobacco-related cancers, especially lung cancer, will almost certainly increase in the years to come.

Indifference - the biggest enemy?

Against the background of all this evidence and the educational efforts of authorities worldwide, what are the chances that in the decades to come, people will change their eating patterns to protect themselves against cancer? Unfortunately, the experts agree that these chances are slim indeed. For one thing, they say, there is no record of any population ever changing from a palatable diet high in fat to a less palatable one which is lower in fat, for health's sake.

To justify this pessimism, it has to be admitted that despite all the evidence and the urging of respected authorities such as those mentioned above, statistics show that people in Western nations are not cutting down on their food and fat intakes. In fact in many countries - such as the US and Australia - obesity is rising. South Africa is no exception in this regard, since several reports havetestified to the high frequency of obesity in our inter-ethnicpopulations, especially among women. Obviously, food consumption in prosperous Western nations - and in 'higher-class' Third World urban populations - is governed mainly by pleasurable taste and hedonisticattraction.

The Cabbage Patch Diet

There has been a lot of discussion in the media about the valuable anti-cancer properties of fruit and particularly of 'cruciferous vegetables'. These are vegetables which have four leaves at the base of the stalk in the shape of a cross - hence the name. Cabbage, brussels sprouts, broccoli and cauliflower all fall into the group. These vegetables also provide us with a large amount of fibre. Along with many other fibrous foods, cruciferous vegetables are rich in vitamins A, beta-carotene, C and E. It has recently been discovered that these vitamins act as important defence mechanisms against damage to tissues and the impairment of their function due to 'free radicals' - compounds which are produced in the everyday working of our bodies.

The vitamins, which act as 'anti-oxidants' or scavengers, tend to lessen the damaging effects of bacteria and other parasites and also have an inhibiting effect on the development of cancer and other degenerative diseases. While these findings may tempt you to rush out and stock up on multivitamins, all authoritative dietary bodies are emphatic that it is infinitely preferable to increase your vitamin intake by eating more plant foods rather than by popping pills. (This applies particularly to vitamin A, which can be toxic in large doses.)

This is borne out by the well-known experience of some populations during World War II. During that time there was a significant drop in the consumption of fat and sugar - simply because they were not freely available - and a marked increase in the intake of less refined bread and of vegetables and fruit. In the populations most affected, there were varying decreases in dental caries, obesity, diabetes, coronary heart disease, constipation and appendicitis. Admittedly there was no clear-cut evidence of a fall in diet-related cancers, perhaps because the length of time these changes were in operation was too short. But the point of this story is that once wartimerestrictions were removed, dietary patterns reverted and frequencies of all the disorders and diseases mentioned returned to their former levels - and then increased.

A recent survey by the American Cancer Society showed that 'only 15% of those polled (white persons) reported that they had made significant changes in the foods they eat because of theirunderstanding of a possible diet-cancer link'. In the Tecumeseh Diet Study (also in the United States) in which peoples' perceptions of change were assessed after a 15-year interval, there was no fall in the intakes of fats and oils. And a survey in the Netherlands indicated that only 4% of the population were consuming a 'prudent' diet.

With increasing urbanization and prosperity, energy and fat intakes are rising in Third World populations to the levels consumed by their white brothers and sisters. Simultaneously, fibre intakes are falling to levels even below those of white populations. Education among urban Third World populations has certainly created an understanding that nutritional deficiency diseases, mainly in children, such as proteinenergy-malnutrition (marasmus, kwashiorkor), can be fought by making appropriate changes, and that adult nutrition is very important in the control of tuberculosis. However, to suggest that their increasingly palatable diet, with higher intakes of animal products, should now be modified to lessen their chances of developing 'killer' diseases in later life seems like a contradiction, and is largely ignored.

In the American Cancer Society study referred to, it came to light that blacks and Hispanics were less inclined than whites to alter their diets so as to reduce their risk of getting cancer - even though these minority groups appeared to be just as aware of the link between nutrition and the reduction of cancer risk. One reason stated was that blacks and Hispanics are more likely than whites to feel that they cannot afford the required nutritious diet. (In America, brown bread costs more than white bread and breakfast cereals, vegetables and fruit are comparatively expensive.)

What are the choices?

First let's look at the choices open to you, which also happen to reflect three different 'schools of thought' on the subject of diet and cancer:

The first choice is to carry on as before, on the grounds that there is still controversy over the extent to which diet is involved in cancer development, that the changes you would have to make are huge and unacceptable, that success is not guaranteed and that in any case there is a large element of individual susceptibility.

Next, there is the stance of the 'activists' who believe that the evidence available is very convincing, that major changes are needed and that they can be put into practice. If you take this approach, you will find a good deal of support in the marketplace, since food products with a low energy or fat content and/or which are high in fibre are becoming more readily available.

Many in this activist group take the holistic approach to avoiding disease, in other words, they believe that we should improve our diets so as to protect ourselves against all diet-related 'killers', not only cancer. Sir Richard Doll, a well-known British medical statistician, expressed this attitude in his 1982 Harveian Oration in London on 'Prospects for Prevention', when he urged:

'...whether the object is to avoid cancer, coronary heart disease, hypertension, diabetes, diverticulitis, duodenal ulcer or constipation ... the type of diet least likely to cause disease is one that provides a high proportion of calories in whole grain cereals, vegetables and fruit; provides most of its animal protein in fish and poultry; limits the intake of fats and if oils are to be used, gives preference to liquid vegetable oils; includes very little dairy produce, eggs and refined sugar; and is sufficiently restricted in amounts not to cause obesity'.

The third group recognizes the truth of the evidence put forward and accepts that dietary changes are required. But their view is that what is needed is simply to eat less and to practice moderation, even to the extent of cutting out alcohol and rich foods. This was the attitude taken by Hippocrates, Galen, Moses Maimonides and numerous other great physician-philosophers of the past.

The bottom line

Firstly, in spite of what might be regarded as a pessimistic tone to this chapter, it must be emphasised that what has been given here is an overview. The results of research may certainly give the experts good cause to be pessimistic - but remember that they deal in statistics. As in so many areas of life, if you as an individual are motivated enough to make the necessary changes, you can make the difference - to yourself and possibly to your family. In fact, considering the wealth of information now available, the prospect of taking individual avoiding action has never been better!

A diet which supplies 25% of energy from fat, and which contains 30g of fibre on a daily basis can certainly be formulated and could, with determined effort, become your personal norm. To do this you will probably have to eat far more of cereal products (which include whole grain breads, unrefined rice and breakfast cereals) and increase your vegetable and fruit intake considerably. You may also have to combat conservatism, inertia and lack of conviction and get used to a 'less palatable' diet - at least until you begin to enjoy foods that are closer to the way nature intended them to be!

It is important to realise that our eating habits are just that - habits - which we have learned and are capable of 'unlearning' if necessary. We don't come into the world craving over-refined breads, fried foods or creamy desserts; our tastes are developed from an early age in our own homes (which is why parents have a particularly important responsibility to guide the development of those tastes). A child who is regularly given white bread sandwiches and sweets for school lunches will probably always regard wholewheat bread and fresh fruit as hard work - yet getting into the habit of eating these and other unrefined foods will undoubtedly put him or her on a healthier nutritional path for life.

In conclusion, the take-home anti-cancer message could be reduced to simply this:

'Stop smoking; eat moderately; eat plenty of plant foods; and seek medical help early'.

Points to ponder

• Recently, there have been major reductions in the occurrence of a number of common diseases, including strokes and coronary heart disease. The full reasons are not known. Hence, it is conceivable that decreases could occur in some cancers, again for reasons not altogether understood. For example, there has already been a major fall in stomach cancer and in some childhood cancers.
• Individuals differ tremendously in their susceptibility to diseases. Obviously, if a parent had colon cancer, or a mother or sister had breast cancer, then the chances of getting such cancers are increased. However, because of differences in the ways people respond to cancer-producing substances, protection against the disease may not require too much avoiding action by a section of the community. This means that even partial reduction in the risk factors mentioned could put some people in a less vulnerable position.
• The dietary and non-dietary measures for the avoidance of cancer are exactly the same as those urged for the avoidance of coronary heart disease and other important diseases. So by following a low fat, high fibre diet you will in any case be protecting yourself against other 'killer' diseases.
• The field of alternative medicine may well produce some useful guidelines for fighting cancer in the future. Already the question is being asked: Are there 'non-orthodox' methods to prevent cancer, or to treat it, or even to cure it? Some interesting recommendations have been made, for example in the diets put forward by Kelley, by Gerson and by Forbes. These diets are largely or wholly vegetarian, with much of the plant food being eaten raw. There are encouraging case- histories which record the arrest and even regression of tumours, but none of the programmes described have been subjected to any form of controlled trial. At present enormous amounts of money are spent on trials in the treatment of various diseases, especially coronary heart disease. Perhaps some money should be devoted to investigating cases of possible 'alternative' cures for cancer. Even the validation of a small number of individual cases would be of great value, bearing in mind the formidable nature of the disease.

Drugs that cause increased excretion of nutrients

Diuretics are frequently taken to correct oedema (water retention) which results from a medical disorder. While they are successful in reducing the excess water level in the body, they also result in the excretion of larger amounts of potassium and magnesium. Patients being treated on a regular basis with thiazide diuretics should therefore increase their intake of foods which are high in potassium such as bananas, orange juice and potatoes.

Alcohol as a drug

Alcohol is regarded as both a drug and a food, since it supplies 29 kilojoules per gram. Because it has mood-altering effects and interferes with the absorption, metabolism and excretion of certain drugs and nutrients, it should possibly be treated with more respect than is usually the case. The reason why the effects of alcohol are felt so swiftly is that it takes a direct route into the system, traveling via the stomach to the small intestine, from where it is quickly absorbed into the blood. A small amount evaporates through the breath and perspiration, but most of it has to be processed by the liver before it isexcreted from the body via the urine.

A regular, excessive alcohol intake decreases the absorption of folic acid, thiamin, vitamin B6, vitamin B12, magnesium, zinc and other trace minerals. High alcohol consumption also tends to go hand in hand with a general decrease in food intake. Alcohol is used as a base in many over-the-counter medications and, ironically, some addicts find all-night chemists a useful secondbest after closing time at the pub!

When combined with the use of other drugs, alcohol can cause serious complications. This is because alcohol itself is a powerful drug and generally speaking, when two or more drugs are taken at the same time they often have a different (and more pronounced) effect than either produces on its own. In addition, if they both act on the same system in the body, their combined effect is often more powerful than might be expected. For example:

• In combination with barbiturates: Both alcohol and phenobarbital (a barbiturate) are depressants. When taken together, even at very low doses, these drugs may increase central nervous system depression and can be fatal.
• In combination with aspirin: Alcohol tends to irritate the stomach lining; when taken in combination with aspirin, which is also an irritant, it can cause internal bleeding.

Other medication: When alcohol is consumed with some antidepressants (ie monoamine-oxidase inhibitors) it may increase blood pressure to a dangerous level. Alcohol combined with antialcohol (Antabuse), antidiabetic and many other medications can lead to abdominal cramps, flushing and vomiting.

Drugs in disguise

Many of us know people who imbibe tea made with loquat leaves for their diabetes, or swear by certain home-brewed herbal mixtures for a multitude of ills. It would certainly be unrealistic to assume that drugs come only in the form of pills or potions created in a laboratory - the early use of the poppy for its narcotic effects is well known - but there are considerable advantages to obtaining one's medication from a pharmacist and not from the garden. These include the fact that the quantity of a compound can be controlled in a pill but not in a leaf, the question of year-round availability and, not least, the convenience.

Some foods are well-known for their adverse drug effects. Liquorice, for example, contains a compound which can cause raised blood pressure if eaten in quantity by people sensitive to this particular substance. Another interesting example (although not of local relevance) is a type of broad bean known as a lava bean' which has a drug-like effect in certain people. Some members of the population in Mediterranean countries have a metabolic defect which causes jaundice, blood in the urine and other symptoms if they eat this variety of bean.

Diet and Drug Interaction

The use of drugs or medication to maintain or restore health has increased tremendously during the past 20 years.

A 'drug' may be defined broadly as any chemical substance that is not one of the basic nutrients (proteins, carbohydrates, fats, minerals and vitamins) and which, when taken in, changes the body's structure or function. Incidentally, according to this definition, even ordinary table salt could be labelled a drug! For the purpose of this article, however, the term 'drug' will mean a non-food substance that is deliberately introduced into the body in order to produce some physiological or psychological effect. Of course drugs act in a variety of different ways, depending on their particular applications, which may be any of the following:

• relief of symptoms (such as headaches)
• prevention of illness (as in the case of vaccines used against diseases such as polio)
• control of chronic conditions such as high blood pressure
• treatment of certain diseases (for example, antibiotics which are used to treat tuberculosis).

How do drugs work?

What determines how a certain drug acts on a specific problem? Why does one have an effect on the blood vessels and another on the lungs? The answer to these questions has to do with the concept of 'receptor sites' - the idea that a drug has its effect only at specific spots within cells where the drug molecule 'fits'. (A molecule is the smallest unit of a chemical substance such as a drug.) These drug molecules do not act on the whole cell, but only at the receptor sites - and only on those cells with receptor sites that are compatible with the drug molecule. The diagram on the following is a representation of the way in which this compatibility works.

Prescription drugs - handle with care!

Whenever your doctor prescribes a medication, make sure that either he/she or your pharmacist gives you the following information:

• The name of the drug (many drugs go by different names)
• The reason you are taking it
• How the drug should be taken (before or after meals, with water, fruit juice or milk, etc)
• The dosage safety level of the drug (to prevent overdosing if you have to use the drug in an emergency)
• How often you should take the drug
• The length of time you should continue to take it
• Whether taking the drug requires any change in your diet or activities (For example, certain drugs may not be taken with alcohol and others may cause drowsiness or interfere with your coordination.)
• What side effects can you expect? (All drugs cause side effects,ranging from the trivial to the serious.)

The drug/diet link

After many years of research, health professionals have established that foods and nutrients do interact with drugs to a significant extent. In other words, medication can have an effect on a person's health and conversely, food can influence a drug's effectiveness. The risk that a drug might have an adverse nutritional effect or that drugs and food might be incompatible becomes particularly relevant when:

• the drug is an 'anti-nutrient' (in other words, it acts like a nutrient even though it is not one)
• a drug which has adverse nutritional effects is taken for a long time
• the patient is taking more than one drug at a time
• a patient's diet is either nutritionally inadequate or the patient is already malnourished
• drugs are used excessively (or there is abuse of prescription or over- the-counter drugs)
• food and/or drugs are not being properly absorbed due to disease
• the patient is not given special diet instructions when necessary
• physicians, pharmacists and dietitians are unaware of the risks involved.

The use of medication may influence nutrient intake, absorption, metabolism or excretion; in the same way, foods or their components may affect the absorption, metabolism and excretion of drugs. To paraphrase this, drugs and foods can interact by one of the following mechanisms:

• Drugs plus foods (nutrients) = changed drug effect
• Drugs plus foods (nutrients) = changed nutritional balance

How drugs affect nutrients

The ways in which drugs alter nutritional balance tend to be subtler and take longer to develop than the effects of food on medication. Drugs may have an influence on food intake due to changes in taste and appetite, they may decrease the absorption of nutrients, change their metabolism or cause them to be excreted in increased amounts (accompanied by diarrhoea and vomiting).

Drugs that affect food intake

Sensitivity to taste is one of the more delicate senses which can be affected fairly easily. Some drugs dull the tastebuds and make eating a less pleasurable experience - which, of course, may have the effect of making you eat less. Three drugs which decrease the sense of taste are clofibrate (a cholesterol-lowering agent), levodopa (an anti-Parkinson agent) and penicillamine (a chelating agent).

One or more of the four basic tastes (sweet, sour, salty and bitter) may be affected. For example, amphetamines decrease sensitivity to sweetness, while fluorouracil (a cytostatic agent) increases it. Diabetics who have to use insulin over prolonged periods find that they experience decreased sensitivity to both salty and sweet tastes. Other drugs - such as allopurinol (an anti-gout agent) - simply leave an unpleasant taste in the mouth.

Drugs that alter appetite

As the table below shows, some drugs directly stimulate the appetite, while others depress it. (Oral contraceptives, for example, tend to have the former effect.)

Drugs that decrease the absorption of nutrients

Drugs can affect the absorption of nutrients in several ways (including changes in the time the food spends in the digestive tract, in the acidity of the stomach, bile acid activity, enzyme systems, mucosal cells, or through binding to nutrients).

Firstly, the absorption of certain nutrients may be affected when the digestion of food is accelerated - a side effect of certain pills given for high blood pressure (ganglion blockers) - or when micro-organisms necessary for digestion are destroyed. In particular, drugs used to prevent indirectly the absorption of cholesterol from food into the body are often accompanied by reduced absorption of other nutrients (especially fat soluble vitamins). As another example, antacids are given to 'mop up' the excess acid in the stomach, but thiamin (vitamin B1) needs an acid medium lower down in the digestive tract to be absorbed, so antacids may impair its absorption.

Drugs that affect nutrient metabolism

Interference with nutrient metabolism can occur when a drug is similar in structure to a vitamin and therefore displaces a vitamin in a metabolic pathway. One example of this is the interaction between methotrexate (amethopterin), a cancer chemotherapeutic agent, and folic acid. Methotrexate kills cancer cells by displacing folic acid

and is therefore called a 'folic acid antagonist'. The problem is that the healthy cells are also prevented from using folic acid, which results in a type of anaemia.

The Pill and vitamin deficiency

The effect of oral contraceptives on nutritional deficiences has received wide attention in recent years. It has been shown that usage of 'the Pill' can decrease the absorption of vitamin B12, vitamin C, folic acid, vitamin B6, riboflavin, magnesium and zinc. On the plus side,however, it increases iron and calcium absorption. Although the Pill does seem to affect absorption and metabolism of many nutrients, there is little scientific evidence that women using it require increased amounts of nutrients to prevent nutritional deficiencies, provided of course that they are healthy and are following a balanced diet. In these circumstances, nutrient levels do not fall to alarming levels.

Some researchers have however established that the depression suffered by certain women who use the contraceptive pill can be due to a deficiency in vitamin B6, which can be treated by supplementation with this vitamin. A number of theories have been proposed regarding the cause of the pre-menstrual syndrome (PMS) and its link to the Pillone of these being that women who suffer from PMS also have low levels of vitamin B6. However, there is as yet not enough scientific evidence to justify fortification of the Pill with vitamin B6, or to suggest that doctors should treat the problem routinely with vitamin B6 supplementation.

Vitamin supplements - the facts

Most doctors and dietitians agree that an adequate diet selected from a range of foods in the Five Food Groups and taken in the recommended portion sizes, will ensure a satisfactory intake of all nutrients, including vitamins. However, it is also recognised that vitamins which are constantly needed in the metabolism can be compared to an integral part of a work force on a factory assembly line. Each worker has a specific and vitally important role to play and his absence can jeopardise the smooth running of the whole system.

In the case of an unsatisfactory vitamin intake, one should first and foremost try to rectify the situation by improving one's diet, as food sources of vitamin also include other essential nutrients - some of which may still be unknown. Incidentally, the reason for choosing a food source rather than a vitamin in pill form is not that one's system absorbs it better - the body is in fact unable to distinguish between natural and synthetic compounds in this way. Each vitamin - whether manmade or naturally available - is a very specific compound with a unique molecular structure which is handled by the body in a particular way.

Supplements should however be considered only if, for some reason, your vitamin needs exceed your dietary intake. For example, people on strict long-term weight-reducing diets, heavy smokers and drinkers, pregnant women taking a less-than-optimal diet to cover the needs of two, or people living in isolated areas (or away on expeditions) who are unable to obtain the necessary variety of foods, may all benefit from vitamin supplements. (Incidentally, a pregnant woman should always take a supplement under a doctor's supervision only.)

A recent study (by Macfarlane et al) on 774 Indian women in Durban showed that 25% had iron deficiency anaemia and an additional 17% showed sub-clinical signs of this deficiency disease. The authors concluded that South African Indian women should receive iron supplementaton during pregnancy, as their cultural dietary habits promote an inadequate intake of this important trace element.

It has also been found that heavy smokers need more vitamin C than do non-smokers, as smoking seems to reduce the availability of vitamin C in food to the body.

The dangers of the overdose

Megadoses of vitamins are a different story. Some people assume that if a small amount of a vitamin supplement is useful under certain circumstances, more would be even better, but this is not so - in fact, abnormally large quantities of the fat-soluble vitamins (A,D,E and K) can be toxic as they accumulate in the body and excesses are not immediately lost in the urine, as is usually the case with water-soluble vitamins. However, care should be taken even with the latter: cases of `rebound scurvy' have occurred in babies whose mothers have taken excessive amounts of vitamin C during pregnancy - with the result that the baby's body reacts as if deprived when it has to depend on its own food intake after birth.

A recent study (by Read et al) in which people in seven states in the USA were questioned about their health beliefs showed that regular supplement users (who were predominantly married Caucasian women between the ages of 20 and 79) believed that supplements decreased their susceptibility to health problems ranging from colds to heart attacks and cancer, and/or reduced the severity of those problems. They also found that the higher the user's level of education, the larger the number of supplements taken, but the bottom line of the study was that more non-users rated their health as 'excellent' than regular users. The authors concluded that it remains a paradox that the well-educated, settled members of the community who are in a position to obtain all their nutrient requirements from a balanced diet, continue to be the most regular users of vitamin and mineral supplements.