By Liam Mannix
Vitamin supplements seem like they should work. But the evidence strongly suggests they don’t. Why? Let’s dive into the data.
What is a vitamin?
A vitamin is an essential nutrient. Deficiency can lead to nasty diseases.
Scurvy is a great example. In past centuries, many sailors would contract the disease, despite having enough to eat. Scientists at the time were baffled. The discovery of vitamin C, an essential nutrient found in fresh fruit and vegetables, saved the lives of thousands of seafarers.
Nicotinamide! Manganese! Zinc! Surely I was deficient in something. Credit: Quentin Jones
Will taking a multivitamin make me healthier?
Sadly, no. Although Australians spend an estimated $3.1 billion a year on dietary and vitamin supplements, there is now a lot of high-quality evidence that multivitamins do not work for people who do not have a vitamin deficiency (and if you think you have a deficiency, you should see a GP and get tested).
Let’s consider an important graph. It’s called the Evidence Pyramid, and it allows you to work out the quality of a piece of scientific evidence.
The evidence pyramidCredit: The Logic Of Science
Some parts of it may surprise you. For example, we in the media often make much of expert opinions – yet in science, expert opinion is considered the lowest form of evidence. This is not to denigrate expertise, but when you read an opinion, you should think: “What evidence is this opinion actually based on?”
The second-highest step on the pyramid is a randomised controlled trial (RCT), the highest-quality direct experiment scientists can do. Sitting on top of the pyramid is systematic reviews, which synthesise several randomised controlled trials.
Let’s go to the RCTs relating to multivitamins.
In a study of 5947 male doctors over 12 years, a multivitamin did not improve brain health or function. In a four-year study of 1708 patients who had suffered a recent heart attack, multivitamins did not cut the risk of further cardiovascular events.
What about the systematic reviews?
Cochrane is an international, independent network of leading scientists who review evidence, looking at the quality of the study and for sources of error or bias, then synthesise it into large reviews that are generally considered the gold standard of scientific evidence. Cochrane pulled together 28 studies of more than 83,000 people. There was no evidence that multivitamin or mineral supplements prevented the normal brain decline that comes with ageing.
A second Cochrane review of antioxidant supplements – beta-carotene, vitamin A, vitamin C, vitamin E, and selenium – looked at 296,707 participants over 78 randomised controlled trials. The conclusion: vitamin E and high doses of vitamin A may actually increase mortality. Yikes!
“The trials that have been done of vitamins have not shown benefit in people who are not deficient. We’re just seeing it time and time again,” said Professor Rachel Neale of the QIMR Berghofer Medical Research Institute.
She would know. Her team just published in esteemed medical journal The Lancet a large (21,315 people over five years) randomised controlled trial of vitamin D supplementation for older Australians.
Vitamin D is a good one to look at because for a long time a lot of groups have argued vitamin D deficiency is quite widespread in Australia. The Australian Bureau of Statistics puts deficiency rates at 23 per cent.
If vitamin D deficiency is as widespread as that number suggests, would a benefit from supplementation show up in Professor Neale’s study? “Almost certainly,” she told me.
The study’s conclusion: no reduction in overall mortality.
“When you look across the body of evidence, the findings are quite disappointing,” said Dr Helen Macpherson, senior research fellow at the Institute for Physical Activity and Nutrition Research at Deakin University (she led a randomised control trial that found no benefit to blood pressure from multivitamins).
“As much as we know these nutrients are important, taking them hasn’t really translated to benefits to health outcomes.”
An important idea about science
Caring about evidence in science is important because there are many, many things that look like they really should work and just don’t. Multivitamins are one example. Similarly, many people with back pain believe it emanates from a dodgy disc, and replacing that disc with an artificial one will cure their complaint – but there is no strong evidence that works either.
Why? Perhaps because, while science has gone a long way to unpicking nature, nature is also infinitely complex. We should stay humble; rather than doing things we think should work, we should look for evidence that they do work.
Why don’t vitamin supplements work?
Supplementing above and beyond your daily vitamin needs does not seem to provide any benefit, says Louis Roller, honorary associate professor in pharmacy practice at Monash University.
“Because vitamins are found to be actually central for life … the thinking goes: a minute amount saves your life, a bigger amount should make you feel good, and a huge amount is going to make you into superman. And that sort of thinking is totally flawed.”
A better magic pill
Studies of vitamin supplements have largely disappointed. But there is an area of research that is a lot more promising: diet.
Being told to eat healthily is all a bit ho-hum, which is a shame because the evidence – proper scientific evidence – suggests eating certain foods really can promote good health.
For this, we have the excellent Australian Dietary Guidelines. More than a boring “eat this, not that” document, this hefty tome is a review of evidence led by the National Health and Medical Research Council.
Consider just eating vegetables. For each extra serve of vegetables you eat per day, there is reasonable evidence that you cut your risk of heart disease and stroke, and suggestive evidence that you cut your risk of oral and prostate cancer. Eating more than one serve of spinach a week is linked to a lower risk of colorectal cancer; eating broccoli or cauliflower likely cuts your risk of lung cancer. One to two serves of tomatoes a day likely cuts your risk of prostate cancer.
One-and-a-half serves a day of fruit is associated with a reduced chance of heart disease and stroke.
Why is this stuff so good for us? The reasons are likely complex because what is in fruit and vegetables is much more complex than the simple chemistry of a multivitamin tablet. Tomatoes contain lycopene, thought to be protective against prostate cancer (particularly when cooked in olive oil). Orange and red fruits contain carotenoids, thought to be important for immune function. Dithiolthiones and isothiocyanates found in broccoli stimulate the detoxification processes.
“Provided you’re eating a range of fruit and vegetables, you’re very unlikely to be vitamin-deficient and a supplement is unlikely to be helpful,” says Professor Neale. “You can work out if you’re going to be vitamin deficient: if you eat white bread and red meat and that’s it, sure, take a multivitamin. My advice to people: just eat properly.”
If you liked this article, consider signing up to receive Examine, a free newsletter, each week in your inbox.