Taking extra vitamins “does more harm than good” and increases the risk of cancer and heart disease, a major study has revealed.
Dr Tim Byers – one of the world’s top cancer experts – examined research papers spanning 30 years.
He looked at three widely taken over-the-counter pills and supplements, vitamin E tablets, beta-carotene and folic acid, and warned against exceeding the recommended daily amount.
Dr Byers said: “We are not sure why this is happening but evidence shows that people who take more dietary supplements than needed tend to have a higher risk of developing cancer.
“When we first tested dietary supplements in animal models we found that the results were promising.
“Eventually we were able to move on to humans. We studied thousands of patients for 10 years who were taking dietary supplements and placebos.
“We found that the supplements were actually not beneficial for their health. In fact, some people actually got more cancer while on the vitamins.”
Folic acid supplements are thought to be taken by thousands of pregnant women each year as it can help prevent spina bifida and other birth defects affecting the brain and spine.
But one study examined by Dr Byers’ team found too much increased the chances of getting cancer by 56%.
The acid – also known as vitamin – is also taken to cut the risk of heart disease and polyps in a colon, which lead to cancer.
But the research found too much in supplement form in fact increased the number of dangerous polyps.
Two trials of beta-carotene supplements found taking more than the recommended dose increased the risk of developing lung cancer and heart disease by 20%.
Meanwhile another trial of 35,000 people between 2001 and 2014 in the States found taking too many vitamin E tablets increased the risk of developing prostate cancer by 17%.
Dr Byers, associate director for prevention and control at the University of Colorado Cancer Center, US, began his study after it emerged two decades ago that people eating more fruit and vegetables were less likely to get cancer.
But long term studies since the 1980s have found taking too many has the opposite effect.
One trial found the chances of lung cancer increased by 18% while another showed a rise of 28%.
Dr Byers said: “We have discovered that taking extra vitamins and minerals do more harm than good.”
He added that most people got their daily recommended doses of vitamins and minerals by eating healthy meals.
He said: “This is not to say that people need to be afraid of taking vitamins and minerals. If taken at the correct dosage multivitamins can be good for you.
"But there is no substitute for good food.”
Folic acid is naturally found in green veg such as broccoli.
Vitamin E is found in foods such as kale and almonds and is taken to boost the immune system.
And Beta-carotene – an antioxidant taken to cut the risk of heart disease and cancer – is found in carrot and mango.
The findings will be presented a US cancer summit this year.
Top nutritionist Dr Carina Norris insisted the problem lies with people exceeding the recommended dose.
She said: “Doctors recommend folic acid to reduce the risk of birth defects and this is not some weird, wacky supplement.
“But I think there is an assumption that if a nutrient is good for you, then more is better.
"But in some cases increasing the dose can increase the risk of cancer and other diseases.”
In 2012 market research firm Mintel found 35% of the adult population took health supplements, although that had fallen from 41% in 2008.