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FOR some people, they are an insurance policy against a less-than-perfect diet. Others take them because they can鈥檛 鈥� or won鈥檛 鈥� eat certain foods. Whatever the reasons, popping vitamin and mineral supplements can feel like a virtuous shortcut to a healthy life.

But in recent months, serious doubts have been raised over whether they are actually any good for us. Take omega-3. For many people, these golden capsules are a way to get the essential fatty acids we are told our bodies need without having to consume oily fish. Yet recent studies indicate that 鈥� unlike eating fish 鈥� taking omega-3 or fish oil supplements does nothing to reduce your risk of heart disease, stroke or early death.

It is a similar story for other nutritional supplements, including multivitamins: the results from a slew of studies on their impact on our health has been underwhelming. In some cases, taking high doses of certain nutrients may even be harmful.

We are also waking up to the importance of the interactions between the different foods we eat and how these influence the uptake of the nutrients they contain. It turns out it鈥檚 not what we eat, it鈥檚 how we eat it.

So are supplements just a waste of money? And if not, which are the ones we should be taking 鈥� and how?

It is only in the past century that we have begun to identify and recognise the importance of the various health-sustaining nutrients found in our food.

The word vitamin, derived from 鈥渧ital amine鈥�, was coined by the Polish chemist Casimir Funk in 1913, following observations that compounds called amines in rice husks could protect chickens from beriberi. This serious condition, which also affects humans, can result in nerve damage or heart failure. We now know that beriberi is caused by a deficiency in vitamin B1, also known as thiamine. Nutritional deficiencies like this were common at the time, but their causes were poorly understood. It wasn鈥檛 until 1926 that vitamin B1, for example, was identified.

The following two decades saw many more vitamins discovered and a growing understanding of how their deficiencies caused common illnesses. This led to the formulation of dietary strategies that cured ailments such as scurvy, rickets and pernicious anaemia, caused by deficiencies in vitamin C, D and B12, respectively. The onset of the second world war prompted the publication of recommended daily allowances for various food groups, vitamins and minerals in many countries. Some nations also began fortifying certain foods with nutrients, such as adding iron to flour and vitamin D to margarine.

However, as well as making populations healthier, this reductionist approach to nutrients has fuelled the growth of what is now a multibillion-dollar supplements industry. This not only focuses on correcting nutritional deficiencies, but also seeks to sell vitamins and minerals to the worried well. In the UK alone, consumers spend 拢420 million on supplements each year, with multivitamin tablets the most popular, followed by fish oil.

On a superficial level, the evidence seems to suggest all this is a good idea. Epidemiological studies, which look at the incidence of disease in specific groups or populations, show that people who eat a lot of fish, or plenty of vegetables, whole grains and olive oil, have lower rates of illnesses such as heart disease and dementia. Many of us have swallowed the notion that a handful of the super-nutrients found in these foods, packaged up into neat once-a-day capsules, can provide the same benefits without the perceived hassle and expense of preparing healthy meals.

The problem is that these benefits aren鈥檛 necessarily found when the supplements themselves are tested. Randomised controlled trials (RCTs) are used to examine whether and how a type of food or a supplement works. In these studies, people are randomly assigned to take either a component of that diet, such as omega-3 fatty acids, or a placebo. And here the results have been mixed. Some RCTs uncover a benefit; others find none at all. 鈥淚ndustry has been attracted to the silver bullets of micronutrients because they are very cheap and easy to formulate into tablets,鈥� says , head of the MRC international nutrition group at the London School of Hygiene and Tropical Medicine. 鈥淚f it had all worked that would have been fine, but the trouble is that it hasn鈥檛. We need to understand why 鈥� and what to do about it.鈥�

Perhaps the biggest recent blow was a published in June by the highly regarded Cochrane Collaboration. The meta-analysis 鈥� a statistical approach that combines the data from multiple RCTs to try to get a more precise estimate of an effect 鈥� looked at 79 studies to assess the long-term impact of omega-3 fatty acids or fish oil supplements on cardiovascular health. It concluded that they have little or no effect on our risk of heart disease, stroke or early death. Other recent meta-analyses support this finding, and have reached similarly disappointing conclusions for the effects of vitamins A, B, C, D and E on various aspects of our health.

Yet some researchers question the relevance of meta-analyses to nutrition research. Unlike drug or surgery trials, where you have a standard intervention and a fairly homogeneous group in which it is being tested, nutrition research is much messier. With a supplement like omega-3 fatty acids, you are pooling together widely disparate studies. They may involve different doses, formulations or even types of the nutrient. Finding an appropriate placebo is also fraught with difficulty. 鈥淚f I do a study with a vitamin E supplement, I have been exposed to vitamin E in utero, throughout my entire life and for the duration of the study 鈥� so there is no such thing as a placebo control,鈥� says , who studies antioxidants at Tufts University in Boston.

Nor do RCTs of supplements often record what else participants are eating, or measure background levels of the nutrient in their bodies. This is important, because supplementing someone who already has adequate levels of a vitamin or mineral is very different to giving it to someone who is deficient in it.

And whereas drug companies will invest large sums of money in high-quality studies because of the regulatory hurdles they must jump to get their drugs approved, there is less incentive for supplement companies to do so. Supplements are generally , rather than medicines. They must be safe for consumption and correctly labelled, but they don鈥檛 have to prove that they improve health. 鈥淭he studies tend to be smaller. They tend to be of a shorter duration,鈥� says at the University of Roehampton in London. 鈥淏ut nutritional supplements are not drugs, so you鈥檙e unlikely to see an effect on people鈥檚 health after taking them for 10 weeks, or even four or five months. You鈥檙e looking at a minimum of a year, and supplement companies are less likely to fund those kinds of studies.鈥�

Meta-analyses often try to account for some of this variability, but the basic problem remains, says Dyall. Still, randomised controlled trials are the best approach we have tried so far. Where does that leave us?

Most nutrition researchers agree that for people who find it harder to eat a balanced diet, either because of allergies or lifestyle choices such as being vegetarian or vegan, taking supplements may be a good insurance policy. There are also other groups in the population who should consider them (see 鈥�Who should be taking what?鈥�).

However, on the issue of whether healthy and well-nourished individuals should take food supplements, expert opinion is divided. 鈥淚 think we have to be aware that, especially at high doses, dietary supplements may not be entirely free of risk,鈥� says , an epidemiologist at the Harvard T.H. Chan School of Public Health in Boston. Too much beta-carotene, for instance, seems to increase the risk of lung cancer in smokers, while excessive vitamin E has been linked to a (greater risk of haemorrhagic stroke), and possibly prostate cancer.

Manson recently on what to tell their patients about nutritional supplements. Her conclusion: 鈥淩outine micronutrient supplementation of the general population is not recommended.鈥�

Prentice agrees. 鈥淢y view is very strongly that people shouldn鈥檛 take supplements unless there is a specific indication 鈥� and in a country like Britain, most people don鈥檛 need supplements.鈥�

Hidden hunger

Yet Blumberg at Tufts University argues that a country鈥檚 wealth is a poor indicator of people鈥檚 nutritional status: you can have plenty to eat, but still be malnourished. 鈥淪ixty-six per cent of Americans are overweight or obese 鈥� and the reason is because they are eating energy-dense, nutrient-poor foods,鈥� says Blumberg.

This 鈥渉idden hunger鈥� doesn鈥檛 only affect people who are overweight or obese. In a joint publication, the US departments of agriculture, and health and human services identified vitamins A, C, D and E, together with choline, calcium, iron, magnesium, potassium and fibre, as 鈥渦nder-consumed鈥� by many people in the US. Those taking a daily multivitamin have intakes that are much , according to work by Blumberg.

鈥淲e know that people in the UK, the US and around the globe are not eating the way they should,鈥� says Blumberg, who led the study. 鈥淲e should try to change that, but I think it is also a prudent and reasonable thing to tell you to take a multivitamin.鈥�

Blumberg, who acts as a consultant for several supplement companies, points to the Physicians鈥� Health Study II 鈥� one of the largest randomised trials of supplements conducted so far, led by researchers at Brigham and Women鈥檚 Hospital in Boston. It in the US aged over 50 for more than a decade and concluded that those taking a daily multivitamin had a modest but significant in the incidence of all cancers.

Further studies are ongoing to see if its results can be replicated, and if the findings also apply to women. 鈥淎s an ageing, older man, I am happy to take modest benefits in any of my physiological systems,鈥� says Blumberg.

For those with a poor diet, then, topping up with supplements can bring them closer to the recommended daily dose. But that doesn鈥檛 always translate into the health benefits you might expect. For one thing, foods contain much more than the nutrients you would find in a typical supplement. This may be another reason why the results from trials of supplements don鈥檛 match observational studies of populations who eat large quantities of foods containing those nutrients.

Not in a pill

鈥淥ne of the main things that is deficient in the UK diet is fibre, and you don鈥檛 get fibre from a pill,鈥� says at the University of Hertfordshire, UK.

Then there are phytochemicals, compounds found in plants, such as carotenoids and flavonoids, that are thought to work in the body to minimise damage to cells caused by free radicals, unstable and highly reactive molecules released by normal body processes. 鈥淭hese would certainly be missing if you are eating a diet of processed foods supplemented with a multivitamin pill,鈥� says Hoffman.

The balance of these nutrients also seems to matter. For instance, the body uses omega-3 oils from oily fish to make substances that dampen inflammation. But closely related omega-6 fatty acids, found in meat, make molecules that promote inflammation. This may be one reason why eating too much red meat is bad for us, and why populations that consume a lot of fish seem to be healthier.

But it isn鈥檛 only important to eat an overall balanced diet 鈥� eating a mixture of foods at each meal also matters. 鈥淗ow much food you eat, when you eat it and the combination of foods you eat it with can have a huge impact,鈥� says at the University of Massachusetts.

In an as-yet-unpublished study, McClements and his colleagues gave people fresh fruit and vegetables to eat either on their own or in combination with emulsions containing various fats or spices, or both. Far more of the nutrients entered the bloodstream when the fruit and vegetables were consumed with an emulsion. When emulsions were combined, the impact was higher still. 鈥淚t suggests that we can design foods to increase the amount of beneficial nutrients absorbed by the body,鈥� says McClements. But it also has implications for the design of clinical trials to test nutritional supplements. 鈥淚f you don鈥檛 control for this 鈥榝ood-matrix鈥� effect, then people could eat the same amount of, say, carotenoids, and one person might absorb a lot, while another would absorb very little,鈥� he says.

Outside of the lab, a good example of this effect is olive oil. It increases the amount of a carotenoid called lycopene that we absorb when we eat tomatoes, because must be dissolved in fat to be transported into the blood. A similar principle applies to the fat-soluble vitamins A, D, E and K.

鈥淭he combination of food you eat and when you eat it can have a huge impact鈥�

Such findings are important for supplement-takers, says Blumberg. 鈥淚f you don鈥檛 take a supplement with food then many of those nutrients are going to be less than optimally absorbed,鈥� he says.

In some situations, these effects could even undermine your health. For instance, calcium supplements have been linked to an increased risk of kidney stones, whereas .

Clearly, we still have a lot to learn about how different foods interact. As we discover more, it may be possible to boost the nutritional value of the foods we eat, as well as design better supplements.

Food, then, is the best source for the nutrients we need. But for those who aren鈥檛 able to get all their nutrition from what they eat, there are some simple things you can do to ensure you get the most out of a supplement: always take it with food, including a little fat, and follow the instructions on the container to avoid overdosing on certain nutrients. And ask your doctor about any supplements you are taking, as some vitamins have been shown to interfere with drugs, such as the blood-thinning medication warfarin, and lab tests.

Most of all, don鈥檛 assume that taking nutritional supplements can compensate for eating an otherwise unhealthy diet. There are thousands of active ingredients in foods 鈥� some of which we are only starting to become aware of. They taste a lot better, too.

This article appeared in print under the headline 鈥淭he truth about supplements鈥�