The truth about vitamin supplements

If you’re one of the many starting this New Year with plans for a cleaner, healthier lifestyle, maybe dosing up on vitamins is on your resolution roster?

You’d be in good company: UK sales of vitamin or mineral supplements were forecast to reach £559 million by the end of 2025, according to market research firm Mintel. But, despite the popularity of these supplements, the scientific evidence about their health benefits is mixed.

Why do people take vitamin supplements?

Vitamins and minerals are essential for our health but they are nutrients our bodies can’t produce on their own – so we must get them from our food, most commonly in the form of leafy green vegetables, fruit, whole-grains, nuts, dairy and lean proteins.

But our increasing reliance on ultra-processed food means many of us may not be getting these nutrients from what we eat: fewer than 17% of UK adults meet the recommended daily intake of five fruit or vegetable portions a day, according to the Department of Health’s latest National Diet and Nutrition Survey.

Vitamin and mineral supplements, sold either individually or as a multivitamin, are designed to provide us with the essential nutrients we may be missing out on. Multivitamins vary in composition by brand but usually combine vitamin A, several B vitamins, vitamins C, D, E and K with minerals such as calcium, magnesium, zinc, iron, iodine, copper, selenium, copper, manganese, potassium and chromium.

What does the science say?

Can vitamin and mineral supplements really fill that nutrient gap? The answer, “as you might expect, is complicated”, said Jasmin Fox-Skelly on BBC Future. Clinical trials have had “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”.

NHS advice is that, “in most cases”, taking supplements is “not necessary” because most people can get the essential nutrients they need from “eating a healthy, varied and balanced diet”.

Some specific groups may benefit, however. Children aged six months to five years are advised to take a daily supplement containing vitamins A, C and D; pregnant women should take vitamin B12 (folic acid) for the first 12 weeks of pregnancy; pregnant and breastfeeding women should take vitamin D daily, and vegans and vegetarians may benefit from taking a vitamin B12 supplement (B12 is almost exclusively found in animal-based foods).

Those over the age of 65 may need extra vitamins D and B12. And there is some evidence to show that, for older people, a daily dose of multivitamins can boost mental and physical function. A US trial, published in The American Journal of Clinical Nutrition, found that they improved memory and cognition in a group of over 60-year-olds and, in a long-running health study of men over 50, published in JAMA, they “modestly but significantly” reduced the risk of cancer.

Are there any risks?

Yes. “Mega-dosing” – taking large amounts of a particular vitamin – can be very harmful. People who have taken too much vitamin D, for example, have been taken to hospital with seizures, which, in some cases, had led to coma or death. Excess vitamin A can cause severe headaches, blurred vision and problems with co-ordination. And huge doses of vitamin C (once erroneously thought to stave off colds) can stomach upset, diarrhoea and, in extreme cases, kidney stones.

It’s also worth knowing that many single vitamin supplements “lack regulation, contain unlisted ingredients, and are not backed up by randomised controlled trials – the gold standard of medical research”, said Fox-Skelly on BBC Future.

Big-brand multivitamins, however, are generally pretty safe and designed to deliver only the recommended daily allowance of each vitamin and mineral, so taking them daily is not risky, said JoAnn Manson, a professor at the Harvard School of Public Health. For most adults, eating a healthy, balanced diet should provide us with all the nutrients we need but I think if anyone’s worried that their diet isn’t healthy enough, “then taking a multivitamin could be a form of insurance”.