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?

Why do people take vitamins and minerals?

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 the hospital after taking dangerously high levels of vitamin D. Consuming 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.