Should we all be taking vitamin supplements?

Vitamin supplements can be an efficient way to add vitamins lacking in our diet. But they're not a silver bullet.

The market for vitamin and mineral supplements is estimated to be worth $32.7bn (£24.2bn), and over 74% of Americans and two-thirds of Britons admit to using them in an effort to improve their health.

However, the pills are mired in controversy, with some studies suggesting they have no discernible health benefits, and others finding they could even harm you. So what does the evidence really say? Should we all be taking vitamin supplements, or just some of us? Does anyone even need to take them?

Vitamins and minerals are compounds that our bodies do not make, but which are nevertheless essential for our health. As we cannot make them, we must get them from our food. Examples include vitamin A; which is vital for good eyesight and maintaining healthy skin; vitamin C, which is essential for a healthy immune system, and vitamin K; which is necessary for blood clotting. Essential minerals, meanwhile, include calcium, magnesium, selenium, potassium, and others. Vitamins and minerals are classed as micronutrients because we only need them in small amounts compared to macronutrients such as carbohydrates, proteins, and fats.

It's fair to say that no supplement will ever replace a healthy and balanced diet. The best way, therefore, of meeting the body's requirement for vitamins is through eating plenty of leafy green vegetables, fruits, grains, nuts, dairy, and fish. However, research also shows that many of us are not managing to adhere to this practice. The rise of fast food, along with ultra-processed products, means convenience often triumphs over a fresh home-cooked meal.

"The average American is eating half of the fruits and vegetables that are recommended," says Bess Dawson-Hughes, a senior scientist at the US Department of Agriculture's Human Nutrition Research Center on Aging, and professor of medicine at Tufts University. "So if you're leaning in that direction, then you are probably missing out on some essential nutrients."

Could multivitamins help fill this nutritional gap? The answer, as you might expect, is complicated. The theory that dosing up on vitamin C could help stave off the common cold spread across the Western world in the 1970s, thanks to people like Linus Pauling, a Nobel prize-winning chemist who claimed that taking up to 50 times the recommended dose of vitamin C could treat anything from influenza, to cardiovascular diseases, cataracts, and even cancer. Although the notion that overdosing on vitamin C could cure the cold has been thoroughly debunked, many still cling to this belief.

Fast forward to today, and influencers are pushing supplements that contain up to 500% or even 1,000% the recommended daily allowance of micronutrients, despite the fact that vitamin supplements in general lack regulation, contain unlisted ingredients, and are not backed up by randomised controlled trials – the gold standard of medical research.

"Mega-dosing" on vitamins and minerals can be dangerous. For instance, there have been instances of people being taken to hospital from taking dangerously high levels of vitamin D. Connsuming too much vitamin D can cause mild symptoms, such as thirst and needing to urinate more frequently, but in severe cases it can cause seizures, coma, and death.

Meanwhile, according to the National Institutes of Health (NIH) in the US, excess vitamin A can cause "severe headache, blurred vision, nausea, dizziness, muscle aches, and problems with coordination. In severe cases, getting too much preformed vitamin A can even lead to coma and death." 

The clinical trials that have been done on vitamins and minerals sometimes have contradictory results, and suggest that whether you will benefit from taking vitamin supplements depends on who you are, as well as the exact micronutrient the supplement contains.

Some of the earliest trials focused on antioxidants, molecules that neutralise harmful chemicals known as free radicals. Free radicals are unstable molecules that react with and rip apart cells and DNA. It might seem to make sense that boosting your intake of antioxidants would help stave off illness, yet studies have consistently showed this is not the case. For example double-blind, placebo-controlled trials led by JoAnn Manson, a professor of epidemiology at the Harvard School of Public Health, found that the antioxidants beta-carotene, vitamin C, and vitamin E had no effect on preventing cancer or cardiovascular disease.

In fact, some studies suggest that mega-dosing on antioxidants can actually harm health. For example, the evidence is mounting from randomised clinical trials that taking large quantities of beta-carotene supplements can increase your risk of lung cancer, especially if you are a smoker. Meanwhile a trial by Manson showed that mega-dosing on vitamin E is linked to an increased risk of haemorrhagic stroke.

"Vitamin E has a blood thinning effect, so high doses of vitamin E make the blood less able to clot, which raises the risk of bleeding in the brain," says Manson.

"There is also a risk that in extremely high doses [of] antioxidants can actually become pro-oxidant, so they actually enhance oxidation."

Taking very high doses of an isolated micronutrient can also interfere with the absorption of other similar micronutrients. For example, one of the reasons that taking too much beta-carotene is thought to be harmful is that it interferes with the absorption of other carotenoids such as lutein, found in leafy green vegetables like spinach and kale.

Vitamin D

Taking more than the recommended daily allowance of antioxidants is not recommended. But what about other vitamins? One nutrient many people don't get enough of is vitamin D, a molecule that is essential for building and maintaining healthy bones. Vitamin D isn't technically a vitamin, as our body can make enough of it as long as our skin receives plenty of sunlight. We can also get it from certain foods. 

Because we don't get a lot of sunlight in the winter months, the public health recommendation in the UK is that everyone supplements with vitamin D from October through March. In fact there is an argument that anyone living north of 37 degrees latitude, equivalent to the US city of Santa Cruz, should take a vitamin D supplement in the winter. This would also apply to anyone living more than 37 degrees south of the equator.

One of the main studies to look at vitamin D was Manson's Vital trial, which involved than 25,000 US adults. It investigated whether taking daily dietary supplements of vitamin D or omega-3 fatty acids reduced the risk of developing cancer, heart disease, and stroke in people with no prior history of these illnesses.

While vitamin D supplements did not affect overall prevalence of cardiovascular disease, strokes, or cancer, there was a 17% reduction in deaths from cancer in the group that took vitamin D. When Manson focused solely on individuals who had been taking vitamin D for two years or more, there was a statistically significant 25% reduction in cancer deaths, and a 17% reduction in advanced metastatic cancer.

"It may be that vitamin D affects the biology of tumour cells to make them less invasive and less likely to lead to metastasis, but it doesn't affect the first diagnosis of cancer," says Manson.

The Vital trial has also shown that vitamin D supplements significantly reduce the rate of autoimmune diseases such as rheumatoid arthritis and psoriasis.

As vitamin D is vital for maintaining healthy bones, it has frequently been claimed that daily vitamin D pills could prevent bone fractures, particularly in elderly people. An early 2000s clinical trial in France found that older people, especially women in a care home setting, may benefit from vitamin D supplementation.

However, subsequent evidence has been mixed. The Vital trial found that vitamin D did not prevent bone fractures, while two other studies, the Vida study, and the D-Health study, also found no significant benefit of taking vitamin D supplements for fractures or falls. However, it could be that the participants of the trials did not benefit because they already had sufficient vitamin D levels, according to Dawson-Hughes.

"None of these trials selected elders with low vitamin D status as a criterion for entry, and it turned out that they were taking place in the time frame when vitamin D was being hyped as the cure for everything, and at least in the United States, vitamin D sales were escalating," says Dawson-Hughes. 

"As a result, the starting vitamin D status of most of the trial participants was already in the desired or optimal range."

Multivitamins

Intriguingly, evidence is starting to grow that popping a daily multivitamin could be beneficial for health, particularly for older adults.

Manson's physician's health study II, which began over 20 years ago, found that the risk of being diagnosed with cancer was 8% lower in people who took a daily multivitamin for 11 years. The greatest benefit was in older participants who were above the age of 70, who had an 18% reduction in cancer with the multivitamin assignment compared to the placebo group.

"It may be because the diet of older people is a little poorer," says Manson. "Or there may be poor absorption of vitamins and minerals, and so this is a group that seems to benefit more." 

Meanwhile, in Manson's 2023 Cosmos trial, people who took daily multivitamins had a 60% reduction in cognitive decline over three years compared to the placebo group. They have also been shown to be linked to a reduction in cataracts.

"These are all age-related diseases – cancer, cataracts and cognition-related memory loss – and multivitamins have been linked in randomised trials to reducing all of them," says Manson.  

So where does this leave us in answering the question – who should take vitamins? Both Manson and Dawson Hughes argue that taking a vitamin pill is unnecessary for the majority of people, and that it is best to get the nutrients you need from eating a healthy, well-balanced diet. Vitamins from food sources are absorbed more easily by the body, plus you get the benefits of other nutrients in foods such as fibre, which is important for gut health. 

Although vitamins and minerals are essential for health, we only need tiny amounts of them to function properly, and studies clearly show that receiving over and above this amount has no benefit. However, clearly there are some of us who could benefit from a multivitamin pill, as long as the concentration of vitamins within it do not exceed the recommended daily allowance.

The NHS in the UK advises if you are pregnant you should take multivitamins and folic acid – which has been clinically proven to reduce neural tube defects in developing foetuses.

There is also good evidence that vegetarians or people who don't eat a lot of fish could benefit from taking tablets containing omega-3 fish oils. The Vital study showed that people given omega-3 fish oils who had a low dietary intake of fish had a 19% reduction in major cardiovascular events compared to placebo. However, those who ate more than one-and-a-half servings of fish per week did not benefit. There are also certain conditions that interfere with the body's ability to absorb vitamins, including Crohn's disease and ulcerative colitis, where individuals may benefit from taking vitamin supplements. Some medications such as metformin, which is used to treat type 2 diabetes, also affect vitamin absorption.

It is possible that adults aged 60 or older may benefit from taking a daily multivitamin tablet to decrease their risk of cancer and slow their rate of cognitive decline, although the jury is still out on this.

Finally, elderly people, especially nursing home residents – who tend to have a restricted diet and spend little time outdoors – may benefit from taking a mixture of vitamin D and calcium supplements to prevent osteoporosis and bone fractures. 

"But multivitamins are very safe, so I think if anyone has concerns about whether they're getting an adequately healthy balanced diet, taking a multivitamin could be a form of insurance to make sure they're getting these essential vitamins and minerals."