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You are here: BBC > Science & Nature > TV & Radio Follow-up > Programmes > Horizon
A handful of pills
The Truth About Vitamins

Read the programme transcript.

Programme summary

Questions and answers

NARRATOR: Britain is in the middle of a health revolution. We're spending three hundred million pounds a year on pills, that some believe to be an amazing natural way to prevent, or even cure, some of our most deadly diseases. And every day, millions of people take vitamin supplements, convinced of their power to keep them healthy.

PATRICK HOLFORD: If you want to lead a long and healthy life, eat right and take supplements.

NARRATOR: But there is a growing anxiety from scientists that our habit of taking large doses of some vitamins could have very different consequences.

CATHERINE COLLINS: For most people there's absolutely no benefit in taking high dose vitamin supplements. At best, they're a waste of money and at worst, they could seriously affect your health.

NARRATOR: Tonight Horizon examines the vitamin revolution, and investigates the facts about the nation's favourite vitamins. Do they work? And are they safe?

NARRATOR: Maddie Walford is thirty-three and leads an active life. She eats well, and exercises regularly. And to make sure she stays healthy she's convinced that she needs to take three special pills every day.

MADDIE WALFORD: I'm definitely a pill-popper. There have been so many jokes going on about, sort of, me in the office, because I line up my vitamin jars every morning and take all the pills. There have been jokes about me rattling when I walk. Some of my family members just think I'm a complete maniac.

NARRATOR: Dina West teaches foreign language students in London.

DINA WEST: How many syllables in this word?

NARRATOR: She has a hectic schedule.

DINA WEST: So it's bungalow.

CLASS: Bungalow.

DINA WEST: Bungalow.

CLASS: Bungalow

DINA WEST: Perfect, ok well done.

NARRATOR: She too is convinced that to feel good and stay healthy she needs extra vitamin pills.

DINA WEST: I take a variety of vitamins, a cocktail of vitamins, probably about eleven a day. I have taken them over a period of twenty-five or more years.

NARRATOR: And then there's Carol, she's fit and healthy and loves hill walking and climbing. And every morning she takes three vitamin tablets.

CAROL REID: On a daily basis, I take vitamin C and vitamin E, and I take a general sort of multi-vitamin.

NARRATOR: She even carries some around with her in her handbag in case of emergencies. And all of them have bought in to the same idea that vitamins are a simple, and above all natural, way to stay fit and healthy. Like millions of people in Britain, they believe vitamin supplements are crucial to a happy and vigorous future.

MADDIE WALFORD: I hope my vitamins will protect me from any form of cancer. Premature ageing. Keep my eyesight, hearing, all my faculties intact as well.

NARRATOR: But do vitamins really have such remarkable powers? Vitamins are nothing more than chemicals that occur naturally in food. Our bodies cannot produce them themselves, and nearly a century ago scientists discovered just how vital they were for our health.

CATHERINE COLLINS: Vitamins are essential for a healthy body, we can't exist without them.

NARRATOR: They found that a whole host of diseases weren't caused by infections from viruses or bacteria, but simply by the lack of these vitamins.

CATHERINE COLLINS: It's very rewarding when a person comes in with a medical condition, or clinical condition, and we can identify that as a vitamin deficiency, treat them with vitamins and see them get better.

NARRATOR: Just by making sure people ate the right vitamins, a whole string of what became known as deficiency diseases could be eradicated. Vitamin A, found in dairy products, liver and fish, prevents blindness and growth deformities. Vitamin C, from oranges and other citrus fruit, has all but ended scurvy. And vitamin D, found in fish, means children need no longer grow up with rickets. Scientists have found our food contained a cheap and simple way to end the suffering of millions of people around the world.

PROF JEFFREY BLUMBERG: The discovery of vitamins was a landmark in modern medicine, it was the first example where we learned that diseases may be caused not just by infectious agents but by the simple absence of a single substance from our diet, a vitamin. That a vitamin deficiency could be the cause of disease and death.

NARRATOR: Today, most of us take for granted a life free from the diseases caused by vitamin deficiency. Doctors now believe that a balanced diet, with a mix of fruits, vegetables, grains and fats, can give you the tiny amounts of vitamins needed to keep you in good health, they have called it the recommended daily allowance. Only in special cases, such as pregnancy, do doctors normally recommend taking higher doses of vitamins.

CATHERINE COLLINS: There are times when extra vitamin supplements are useful, for example, folic acid is important in preventing birth defects in babies, so it's very important for women considering pregnancy to take a folic acid supplement, before they're pregnant, and for the first twelve weeks of pregnancy.

NARRATOR: But forty years ago, someone came along who would transform the world's perception of vitamins. Someone so powerful that he would take them out of the hospital and the doctor's practice and into millions of homes and high streets. Linus Pauling was a scientific superstar.

LINUS PAULING: For example if we consider a helium atom with the nuclear atom.

STEPHEN LAWSON: As Albert Einstein remarked, Linus Pauling was a genius.

NARRATOR: He was so brilliant that he is the only man to win two individual Nobel Prizes, once for chemistry and once for peace.

STEPHEN LAWSON: Two Nobel Prizes gave him astonishing scientific credibility. In addition to being an incredible genius, he was also a very charming and charismatic man.

NARRATOR: Though he died ten years ago, his work on the structure of molecules is still the basis of modern science.

STEPHEN LAWSON: Until Pauling came along to revolutionise chemistry, the nature of the bond that held atoms and molecules together really was not well known. And Pauling provided this foundation for modern chemistry.

NARRATOR: It seemed he could go effortlessly from one area of science to another.

STEPHEN LAWSON: He had an encyclopaedic knowledge of chemistry, physics, biology, medicine.

LINUS PAULING: As a chemist, I have a background of knowledge that permits me to appreciate the new ideas, but I also like very much having new ideas myself.

NARRATOR: And in the late 1960s, the great man had a huge idea. Pauling became convinced that vitamins could not only prevent deficiency diseases, they could do something far, far bigger. He believed they had the power to prevent diseases that had nothing to do with deficiency at all, diseases which threatened every one of us, like cancer. Heart disease. They could even delay ageing. The key, according to Pauling, was to take them in huge doses.

STEPHEN LAWSON: It was a very revolutionary idea because at the time most conventional scientists and nutritionists were interested in vitamins with respect to their associated deficiency diseases, and not achieving optimal health by increasing the intake of vitamins.

NARRATOR: When Pauling took his message to the world, the public loved it. It was after all the 60s, and vitamins seemed to offer a safe, easy remedy to the illnesses we most feel. You didn't always need big pharmaceutical companies and drugs, you just needed nature's remedy in pill form. The message was simple. If the amount of vitamin C required to stave off scurvy was ten milligrams, and could be found in a slice of orange, then thousands of times more, the equivalent of over one hundred oranges, and more than two hundred and fifty times the recommended daily allowance was even better. Because that could prevent you from catching the most irritating of diseases, the common cold.

LINUS PAULING: The proper intake of vitamin C helps keep one from catching colds.

NARRATOR: To this claim, Pauling's claim that huge doses of vitamin C can prevent you catching a cold is popularly believed to be scientific truth.

WOMAN: It helps ward off colds.

WOMAN: Helps you to prevent colds.

MAN: Prevents colds and flu, that's what I take it for.

MAN: A Nobel Prize winner says that it cures the common cold.

NARRATOR: Pauling's belief in taking large doses of vitamins has inspired a whole new breed of health advisors. Patrick Holford is one of the most popular and well known. He is the author of more than twenty books, promoting the use of supplements for good health.

PATRICK HOLFORD: This is vitamin A, it's great for your skin.

NARRATOR: He has founded an institute for optimum nutrition.

PATRICK HOLFORD: This is vitamin B, it's good for energy and it helps to keep your mood even.

NARRATOR: He believes that optimum health comes from physical activity, a good state of mind, and a nutritious diet. All topped up with large daily doses of vitamins.

PATRICK HOLFORD: I believe that taking vitamin supplements, not only adds years to your life, but also adds life to your years.

NARRATOR: Between them, Pauling and the nutritionists, have helped spawn a vast industry. In supermarkets, health food shops and chemists, you can buy vitamin supplements. All marketed as a safe, natural way to help you stay feeling good, looking beautiful, and being healthy. In Britain alone, we spend three hundred million pounds a year on these pills. Carol Reed is a typical customer. She buys some of the twenty million pounds worth of vitamin C tablets that are sold every year. It is far and away the most popular vitamin, and she takes five hundred milligrams a day, nearly nine times the recommended daily allowance. And all because she has complete faith in the theory of Linus Pauling.

CAROL REID: I take vitamin C because I believe it actually builds my immune system to the extent that I can fight off the common cold.

NARRATOR: But does vitamin C really prevent the common cold as Linus Pauling believed? What is the actual scientific evidence? On America's west coast is Oregon State University. It is home to the Linus Pauling Institute, which was founded to continue his research in to vitamins.

PROFESSOR BALZ FREI: I think Linus Pauling was one of the first to really understand the role of vitamins above and beyond preventing deficiency disease. And he called that orthomolecular medicine, so the right molecule at the right concentration, which can provide optimum health, and not just prevent deficiency disease.

NARRATOR: Professor Balz Frei is one of the world's leading experts on vitamin C. He has studied the evidence from clinical trials involving thousands of volunteers from across the world, designed to investigate Pauling's claim that large doses of vitamin C fights the common cold. And at first it seems that Pauling really was on to something. Vitamin C does have an effect on the common cold, once you've already caught it.

PROFESSOR BALZ FREI: I think there is a role for vitamin C in shortening the duration of the symptoms of the common cold, by about twenty per cent. And ameliorating the symptoms, so you're not as sick as without taking vitamin C supplements, and I think he was right with that.

NARRATOR: But then Professor Frei examined Pauling's central claim, the idea that first sparked the vitamin revolution.

LINUS PAULING: The proper intake of vitamin C helps keep one from catching colds.

NARRATOR: And for this claim, that huge doses of vitamin C can prevent you catching colds in the first place, the results are very different.

PROFESSOR BALZ FREI: I've looked at the evidence that vitamin C can prevent the common cold, but for the general population there is really no evidence from scientific studies that vitamin C can lower the incidence of the common cold, or prevent it in the first place. So taking vitamin C supplements is not going to help prevent the common cold.

NARRATOR: In other words, the director of the very institute set up to pursue Linus Pauling's work, now believes that the great man was wrong. Taking large doses of vitamin C does not prevent you from catching the common cold. Of course, that won't stop millions of people like Carol from taking it.

CAROL REID: The results of those trials are not going to influence the fact that I go out and buy vitamin C on a regular basis, and take vitamin C, because for me taking a vitamin C tablet will help my body, prevent my body catching a cold.

NARRATOR: And while Carol is unlikely to be doing herself any harm, the fact remains that the overwhelming body of scientific evidence says that for most people in Britain, taking high doses of vitamin C to prevent getting colds, is a waste of money. Of course, there are other reasons why people decide to take vitamin C supplements. It's one of a special group of vitamins called antioxidants. Vitamins of such power, the believers ascribe to them properties that are truly remarkable.

PATRICK HOLFORD: I believe they can protect your brain, your body, your arteries, and not only slow down the ageing process but keep you free of diseases, from heart disease, cancer, Alzheimer's, all the tragedies of twenty first century living.

NARRATOR: These huge claims are all because of how antioxidants work on something in our body called free radicals. Free radicals are unstable molecules that exist in our cells. They attack other nearby molecules, stealing an electron and with it an atom to become stable again. When the attacked molecule loses that atom, it becomes a free radical itself, beginning a chain reaction. Normally the body can handle these free radicals, but if there are too many, cells can be damaged with devastating consequences.

PROF JEFFREY BLUMBERG: Free radical damage is associated with a number of diseases, like heart disease and cancer, and macular degeneration, but we also think that free radical damage to cells and tissues is a fundamental part of the ageing process itself, why we grow old. It's in part due to the activity of free radicals.

NARRATOR: But antioxidants, in particular vitamins A, C and E, mop up the free radicals and stop them from attacking our cells. A simple demonstration, with nothing more than a piece of steak, can show just how good vitamin E is at preventing free radical damage, or oxidation.

PROF MARET TRABER: When you look at it in the grocery store it's red and beautiful. That's the vitamin E that's protecting the meat from oxidation. What I'm going to show you is what happens if you destroy the vitamin E. So we're going to take this chemical and place it on the surface of the meat. That's going to actually destroy vitamin E.

NARRATOR: Once the vitamin E is destroyed the cells in the meat are swamped by free radicals. Within just a few minutes the meat starts to turn brown and rancid, the cells have been fatally damaged.

PROF MARET TRABER: And the same thing would happen to your body if you didn't have the protective effect of vitamin E.

NARRATOR: Many large studies have shown that people who eat a diet rich in antioxidants, found in foods such as fruits, vegetables, grains and fats, live longer, healthier lives.

PROFESSOR FRANK KELLY: The studies that have been done in respect of food indicate that individuals with a good quality diet, with lots of anti-oxidant vitamins present have a decrease incidence of the major diseases.

NARRATOR: But some people think that the amount of antioxidant vitamins you can get, simple by eating a balanced diet, are not enough. They believe that you need to take much more, and that means popping high dose pills. Dina West is one of them, she takes a high dose vitamin E capsule every day, it contains forty times the recommended daily allowance.

DINA WEST: Vitamin E is an antioxidant, and it helps to fight the nasty free radicals, which are toxins. And I like that, I don't want anything nasty racing around in my body thank you very much. And they help, they help me a lot.

NARRATOR: But recently there's been a piece of research that suggests Dina could be missing any benefit from her vitamin E supplements. And it's all because of how she takes them. She's often in a rush, skips breakfast, and so swallows her pills with a glass of water on an empty stomach. The idea that Dina could be missing any potential benefit from vitamin E came from Maret Traber at the Linus Pauling Institute. Vitamin E is a fat soluble vitamin, that means it has to be eaten with some fat to be absorbed. So popping a pill just with water on an empty stomach like Dina does, might be almost no good at all. In an experiment Professor Traber gave volunteers a vitamin E pill and a glass of virtually fat free skimmed milk. She then analysed their blood to see just how much vitamin E had been absorbed. The results were striking.

MARET TRABER: When the subjects took their vitamin E pill with a glass of milk, hardly any was absorbed. I think the implication of our study is that if you take a vitamin E pill, you'd better take it with some food, you'd better take it with some food that has fat in it, or you're not doing yourself any good.

NARRATOR: In other words, if Professor Traber is right, then anyone who takes vitamin E without a fatty meal could be wasting their time. But there was something unusual about her experiment. Professor Traber used specially manufactured pills, she did not use a commercially available product. Horizon decided to investigate Professor Traber's ideas further. Just how important was it to take a vitamin E pill with a fatty meal? We commissioned King's College London, one of the world's leading research centres on vitamin E, to run the experiment. In charge was Professor Frank Kelly. The pills he would test had been bought in a high street chemist. Dina and four other volunteers agreed to take part in a ground-breaking study. Each volunteer was told to make sure they had an empty stomach, then they were given a vitamin E pill with three different drinks. Day 1, a glass of water and no fat at all. Four days later, a glass of full fat milk. After another four days we upped the fat content again and gave them a milkshake containing over forty per cent fat. After each pill was taken, the volunteers returned every four hours to give a blood sample so we could see how much of the vitamin E they had absorbed. If Professor Traber's theory was right, the volunteers should absorb very little of the vitamin E when the pill was taken with water, and they should absorb it very well when it was taken with the fatty milkshake. With the blood samples complete, Professor Kelly analysed the data. And after several weeks of nervous waiting, Dina returned to get the results.

PROFESSOR FRANK KELLY: So, it's time for the, the truth.

DINA WEST: Good.

PROFESSOR FRANK KELLY: Here are the results. You were actually subject number 5 in the study.

DINA WEST: Ok.

PROFESSOR FRANK KELLY: And you can see here that this is with water.

DINA WEST: Yes.

PROFESSOR FRANK KELLY: This is with full fat milk, and this is with the milkshake. So, contrary to our expectations.

DINA WEST: Yes.

PROFESSOR FRANK KELLY: You actually have absorbed as much with water as with either the other two diets. So, the water was as good for you as the milk and the milkshake, which as I say was a surprising result to us.

NARRATOR: Contrary to every thing Professor Kelly expected, the amount of fat taken with the pill had made very little difference to Dina. And it wasn't just Dina's results that were a surprise. The group overall showed a similar pattern. When Dr Kelly looked for an explanation he found that the capsules used in the Horizon experiment contained a tiny amount of fat. The fat is often added to make the vitamin E more runny and easier to handle. But he hadn't suspected that it was enough to allow absorption, and it might explain the unexpected results.

PROFESSOR FRANK KELLY: The only possible explanation I have at this point is that there was enough fat in the vitamin E supplement to allow that absorption to occur.

NARRATOR: In other words, it means that Dina can carry on taking her vitamin E just as she does today. However, most doctors recommend people to get the vitamin E they need from food. And because the Horizon study was small and tested only one product, for people who decide to take vitamin E supplements, it may still be advisable to take them after a meal to give themselves the best chance of absorbing the vitamin E. But there is another antioxidant vitamin which is popular and about which scientists are much more cautious. Vitamin A. In vegetables there is a chemical called beta-carotene, which your body converts in to vitamin A. It is found in carrots and leafy green vegetables. And it's seen to have an extraordinary health benefit. Studies have shown that people who eat a diet rich in beta-carotene are much less likely to develop lung cancer. And this seemed to offer a genuine breakthrough. Demetrius Albanes is one of the leading cancer experts in America. He hoped that beta-carotene pills could be a simple way to fight one of our biggest killers. So he and his colleagues organised a study to confirm that high dose pills really could save millions of lives.

DEMETRIUS ALBANES: We were thoroughly expecting to see a reduction in lung cancer incidents. We designed the study actually to be able to detect at least a twenty five per cent reduction and I would say many of us at the time would have estimated we might observe a twenty five to fifty per cent reduction in lung cancer.

NARRATOR: Fifteen thousand people were given high dose beta-carotene pills, each one containing the equivalent of six carrots. To have the best chance of seeing whether the pills really could prevent lung cancer, they were given to people most likely to develop it, smokers. For eight years a team of safety experts monitored the volunteer's health. And it seemed that everything was progressing normally. But then, just before the trial was due to end, they called a surprise meeting.

DEMETRIUS ALBANES: The key investigators were called in to the committee, and they informed us that we had some effect happening with respect to the beta-carotene. They informed us that we in fact had a small increase in lung cancer in the beta-carotene group.

NARRATOR: It seemed that beta-carotene pills, which every one had hoped would prevent lung cancer, were having the exact opposite effect.

PROFESSOR FRANK KELLY: I think there was a mass panic to begin with because this is really the way we expected the science to work.

NARRATOR: It was a devastating result. The people taking the pill had shown an eighteen per cent increase in lung cancer.

PROF JEFFREY BLUMBERG: My first response on hearing these results was being stunned and not really believing it. I thought the results were a fluke.

NARRATOR: But it was no fluke, eighteen months later the news about beta-carotene got even worse. Another similar study was stopped two years early.

CONTRIBUTOR: An interim analysis showed that there was a twenty eight per cent increase in the number of lung cancers in those taking the intervention.

NARRATOR: Scientists still do not fully understand why beta-carotene appears so beneficial in food but seemed to have such a devastating effect on smokers when taken in a high dose pill. But because of these studies, in 2003 safety experts in the UK advise smokers not to take beta-carotene supplements. And advised everyone to limit their daily intake from high dose pills. These studies were a salutary lesson that vitamin supplements were not just some harmless natural remedy. In high doses they could have unexpected and dangerous consequences.

PROF JEFFREY BLUMBERG: When the results of the adverse effects of beta-carotene were confirmed in later studies, we began to understand that high doses in certain populations and under certain circumstances really could be harmful. I think we learned a great lesson.

NARRATOR: So great is the fear that large doses of some vitamins can be dangerous, that some scientists are now sounding the alert about another common form of vitamin A. It's called retinol. Maddie Walford is one of the many people who take this type of vitamin A supplement every day. She takes a high strength pill containing nearly three times the recommended daily allowance.

MADDIE WALFORD: The reason I take a high strength vitamin, to be honest I'm not quite sure, but I thought it was probably because it had more potency. And would therefore, therefore be you know worth the money.

NARRATOR: But the idea that the more vitamin A you consume the better can lead to terrible consequences if taken to excess. Doctor Rob Goldin is a pathologist at St Mary's Hospital in London. He specialises in diagnosing the cause of liver disease and recently he was given a biopsy from a sick patient in his thirties.

DR ROB GOLDIN: I was referred some slides on a liver biopsy from a patient of another hospital to try and ascertain the cause of liver disease because there was no obvious cause. The first thing I did when I examined the liver biopsy was to look for evidence of viral hepatitis, or alcoholic liver disease, the commonest cause of liver damage. I couldn't see any of these.

NARRATOR: So Doctor Goldin had to look for another explanation, and he knew that vitamin A might hold the answer.

DR ROB GOLDIN: If you consume more vitamin A each day than your body actually require then the vitamin A will accumulate in your body because there's no easy way of excreting it and the place where it accumulates is the liver.

NARRATOR: Doctor Goldin then examined the sample to look for the telltale signs of vitamin A damage.

DR ROB GOLDIN: On this half of the screen you can see some normal liver with normal healthy liver cells. On this half of the screen you can see the liver biopsy from the patient, and in this slide the scar tissue stains blue, and you can see there's blue scar tissue surrounding the liver cells. Now the pattern of this scar tissue deposition in this patient made me think that the liver disease could be caused by vitamin A, and that this could be the explanation of his liver problems.

NARRATOR: But surprisingly the patient's medical records made no mention of him taking vitamin A supplements.

DR ROB GOLDIN: I contacted the clinician at the referring hospital, to check whether his patient had been taking excessive amounts of vitamin A. He went back to the patient. On close examining the patient said they had been taking excessive amounts but hadn't mentioned this earlier because he didn't consider vitamin A to be a drug.

NARRATOR: Cases like this are extremely rare, they normally involve taking the equivalent of many high strength vitamin A pills, every day, for years. But they serve to remind us all that vitamin A, in the form of retinol, although not a drug, is a powerful chemical. And today, the safe level of vitamin A consumption is the subject of fierce debate. Patrick Halford recommends people take 2500 micrograms, that's over three times the recommended daily allowance, because he is convinced that it will lead to better health.

PATRICK HOLFORD: Vitamin A is absolutely essential for every single cell in the body. It helps to protect your DNA, it helps to keep your skin healthy, it helps to protect your body cells from infection. So it's an essential vitamin, you need it every day.

NARRATOR: But in recent years evidence has emerged that suggests even this amount could be harmful. And everyone needs to think carefully about the amount of vitamin A they consume. Sweden is a prosperous country, where people live long and healthy lives. But surprisingly it has one of the world's highest rates of a debilitating disease, osteoporosis. It most often affects women over fifty. And its crippling condition gradually thins and weakens your bones, increasing the risk of fracture. But for years it has been a mystery why the disease is so common.

PROFESSOR MELHUS: When we look at known risk factors for osteoporosis, such as age, smoking, physical activity, they can partly explain why it's so common with osteoporosis and bone fractures in Sweden, but that can not explain everything. And then, even more surprising, is that we have a diet rich in calcium, which should protect our bones.

NARRATOR: So Professor Melhus began to look for another explanation. And there was something in particular about the Swedish diet that made him suspicious. It was exceptionally high in vitamin A.

PROFESSOR MELHUS: We eat dairy products, oily fish, such as herring and salmon, we consume cod liver oil, vitamin supplements, all which contain high levels of vitamin A, and on top of that we are the only European country which fortifies low fat dairy products with vitamin A.

NARRATOR: This triggered an alarm for Professor Melhus. Because there was evidence that huge doses of vitamin A damaged animal bones.

PROFESSOR MELHUS: Since we knew about these harmful effects of vitamin A on animal bones, we wanted to see if this also could be occurring in humans.

NARRATOR: So Professor Melhus launched his own investigation. From a database of sixty six thousand women aged over forty, he looked for cases of bone fracture. He then checked the diet of these women to see if their vitamin A intake was particularly high. And the results seemed to confirm his suspicions.

PROFESSOR MELHUS: When I saw the results from our study I was really surprised, although I knew the experiments done in animals, it was hard to accept the fact that vitamin A, a vitamin, had negative effects on bone in humans.

NARRATOR: Professor Melhus then went further. He did a series of bone scans to work out what level of vitamin A was linked to weaker bones. His results suggested that long term consumption of even relatively small quantities of vitamin A were having a dramatic effect.

PROFESSOR MELHUS: What we saw was that a vitamin intake above 1.5 milligrams per day, which is approximately twice the recommended daily intake, there was a reduction in bone density about ten per cent, and the risk of hip fracture had doubled.

NARRATOR: If Professor Melhus was right then the implications were staggering. An intake of 1.5 milligrams per day is a level that can be reached from food alone. And it will be exceeded by taking just a single capsule of some high strength vitamin A supplements. So, tablets that people take every day to improve their health might actually be slowly, silently, weakening their bones. For Professor Melhus, the implication is clear.

PROFESSOR MELHUS: Based on our research I think people should continue to eat a healthy, normal balanced diet. But since supplements containing high levels of vitamin A may have adverse effects, I cannot recommend people to take them routinely.

NARRATOR: Professor Melhus has now done another study that suggests the same risk also applies to men. And since his original work, studies from America have supported his findings, but there has been some other research which has not found the same link.

PATRICK HOLFORD: The evidence linking osteoporosis with, with relatively small amounts of vitamin A consumption, I'm not convinced by it. There are, there are studies that show no such link, and it simply doesn't make sense, because we're talking about levels that we could easily eat and have eaten for millions of years. So at the moment I'm simply not convinced.

NARRATOR: But some scientists see the research very differently. Professor Andrew Renwick is a clinical pharmacologist at Southampton University, and one of Britain's leading experts on vitamin safety. For four years he was part of an independent committee advising the government on the safety of vitamins. He takes the emerging evidence about vitamin A very seriously.

PROFESSOR ANDREW RENWICK: I am concerned, although the, the evidence is not totally consistent, there have now been a number of studies showing a link, and I'm convinced that a high intake of vitamin A will give an increase risk of bone fracture.

NARRATOR: In 2003, the safety committee Professor Renwick was part of reported that they could not yet define a safe maximum intake of vitamin A. But they did sound a warning.

PROFESSOR ANDREW RENWICK: We evaluated all the data, and concluded that an intake of more than fifteen hundred micrograms per day, of vitamin A, could be inappropriate. Primarily because of an increased risk of bone fracture.

NARRATOR: Fifteen hundred micrograms is less than the amount found in some high dose vitamin A supplements, available over the counter. Maddie Walford has been taking a pill containing over two thousand micrograms of vitamin A for more than a year. We asked Catherine Collins, chief dietician of St George's Hospital in London, to analyse her diet and advise her what to do.

CATHERINE COLLINS: What you can see from our dietary analysis is that you've actually got a very healthy diet. When we look at your vitamin A level, we can see that you're getting the full amount of vitamin A you need in your diet, from your small amount of animal source and the rest of the fruits and vegetables that you eat.

MADDIE WALFORD: Right.

CATHERINE COLLINS: What is of concern is the fact that you're taking a very high dose supplement of vitamin A.

MADDIE WALFORD: Oh right.

CATHERINE COLLINS: And at this level there is a potential risk of you developing osteoporosis and fracture risk with long term usage.

MADDIE WALFORD: Right. Do you think that with the amount of vitamin I've been taking for the length of time I've been taking it I will have done myself any, any physical damage?

CATHERINE COLLINS: If you've only been taking this for a year or so it's probably fine. But it's not a supplement we'd recommend you take long term. It certainly is associated with an increase fracture risk.

MADDIE WALFORD: I was very surprised about the link between osteoporosis and vitamin A and risk of fracture, because I'd never associated vitamin A with osteoporosis. It's definitely changed my mind about taking that, I'm actually going to be stopping it as of today, because it clearly doesn't do any good for me personally, and it might do more harm than good.

NARRATOR: Vitamins without doubt are vital to our health. And it remains possible that high dose vitamin supplements will one day be proven to protect against illnesses like heart disease and cancer. But so far, definitive evidence for these claims remains largely elusive. And as we discover more about some vitamins, it is increasingly clear that in large doses they can have unexpected, and sometimes dangerous consequences. Until we understand more about these powerful chemicals, most doctors would advise everybody to seek advice before joining the high dose vitamin revolution.

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Eat something green, something red and something citrus every day.

Health: Vitamins and minerals
If you're sports-mad do you need to take vitamin supplements?

Health: Vitamin dangers
Take too much vitamin B6 and you could cause nerve damage...

 Elsewhere on the web

The UK Food Standards Agency
Advice on food and safe levels of Vitamin consumption.

British Dietetic Association
Find out more about state registered dieticians.

Institute For Optimum Nutrition
More information about Patrick Holford and his institution.

The Cochrane Foundation
Free, readable summaries of the evidence for health claims including vitamin C and the common Cold.

The Linus Pauling Institute
More on Linus Pauling and his research into vitamins.

National Institutes of Health
A good American summary of recent research about the safety of vitamin A and beta-carotene.

The BBC is not responsible for the content of external websites

All content within BBC Science & Nature is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. The BBC is not responsible or liable for any diagnosis, decision or self-assessment made by a user based on the content of the BBC Science & Nature website. The BBC is not liable for the content of any external internet sites listed, nor does it endorse any commercial product or service mentioned or advised on any of the sites. Always consult your own GP if you're in any way concerned about your health.


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