The Truth About Supplements

Supplements are often the first question I get asked about.

The magic bullet that will improve your overall health and wellbeing in one or two (or sometimes 6) tablets a day! There are few, but critically important populations that do need supplements. For example, any woman of reproductive age is recommended to take a multivitamin every day to get sufficient folic acid. Folic acid supplementation reduces the chance of having a baby with neural tube defects. These defects occur very early during gestation, often before a woman knows she is pregnant. 

The main challenge in determining if they work or not is the one size fits all approach. There is A LOT of research done on supplementation. It is a multibillion-dollar industry that benefits from making health claims demonstrating the efficacy and or effectiveness of their products. 

If you think about all of the different supplements out there and all of the different health outcomes they purport to benefit, you are going to find some that have evidence to support their use. For example, if you look at the Cochrane Library Database* that houses the GOLD standard in reviews of the evidence for clinical studies and type in “probiotic” you will see that there are 56 reviews on them spanning topics such as “probiotics for treating eczema” to “probiotics for non‐alcoholic fatty liver disease and/or steatohepatitis”… And you will see there are over 7381 individual trials on them! 

So do they work? Maybe. It depends on what you are trying to measure. 

One of the biggest issues (and sometimes dangers) with recommending supplements is that there is an assumption that a particular naturally occurring vitamin or mineral in food, if taken in isolation and in high doses will lead to better health as we believe we understand the mechanisms by which it works.

Let’s take vitamin A or E as an example. These are antioxidants that combat free radicals. We assume vitamin A or E will reduce the damage to cells caused by free radicals, including damage to our DNA, which may play a role in the development of cancer. Seems logical these vitamins could help reduce cancer. Better load up on antioxidants supplements. 

Well they did just that back in the 1990s and early 2000s with a series of studies that were designed to improve cancer outcomes in high risk groups. 

One study conducted in the 1990’s wanted to test if the health effects of vitamins found in fruits and vegetables, retinol and beta carotene, (think vitamin A), which had been seen to be in higher concentrations in people with lower rates of lung cancer, would be the same when taken as a supplement. 

Over 18,000 men and women at a high risk of developing lung cancer were either assigned a beta-carotene and retinyl  palmitate (vitamin A) supplement taken daily or a placebo. The study was stopped ahead of schedule because participants who were randomly assigned to receive the beta-carotene and Vitamin A were found to have a 28% increase in incidence of lung cancer and a 17% increase in incidence of death compared to the placebo group. 

A second study in 2001 was conducted to determine the long-term effect of vitamin E and selenium on reducing the risk of prostate cancer in approximately 34,000 relatively healthy men >55 years. It was assumed these antioxidants would reduce the risk of cancers in high enough doses. 

Oral selenium and vitamin E was planned to be taken for a follow-up of a minimum of 7 and maximum of 12 years at very high doses. It was found that the risk of prostate cancers in men that were supplemented with vitamin E was 17% greater compared to a placebo (no supplement). In the selenium group there was also an increased risk but it wasn’t statistically significant.

So what does all of this mean?

Both of these studies highlight that caution should be used when recommending or using high doses of vitamins or micronutrients. Naturally occurring dietary constituents (i.e. vitamins and minerals) are part of normal physiology, and either deficiency or excessive doses are harmful. 

It doesn’t mean you shouldn’t adhere to advice given to you by your doctor or dietician if treating a medical condition, but it does show that the assumed benefit of a vitamin or mineral is not always correct when taken in isolation. 

This lack of benefit/potential harm from single antioxidants was later confirmed in 2012 with one of those GOLD standard Cochrane reviews I was talking about before that looked at Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases

This review included 78 clinical trials with 296,707 participants randomised to antioxidant supplements (beta-carotene, vitamin A, vitamin C, vitamin E, and selenium) versus placebo or no intervention. They found, wait for it, an increased risk of mortality was associated with beta-carotene and possibly vitamin E and vitamin A, but was not associated with the use of vitamin C or selenium, with absolutely no benefit of antioxidant supplements in the general population or in patients with various diseases.

Ok, but you are really here for me to tell you whether fish oil is good for you or not. Right? Well. 

A recent large Cochrane Review assessed the effects of increased intake of fish and plant-based omega-3 fats on all-cause mortality, cardiovascular events and blood lipids levels, mainly via capsules, as many people believe that taking omega-3 supplements reduces risk of heart disease, stroke and death. 

The review included 86 clinical trials and over 120,000 participants that compared greater omega-3 intake versus lower omega-3 intake for at least a year. The review found that increasing EPA and DHA (omega-3 fats found in fish) had little or no effect on all cause mortality, cardiovascular death, stroke, or heart irregularities.

So, what’s the take away from all this?

Some supplementation is necessary for some people

There will be new studies that may change what we know on some of the topics I have shared with you here, and if they do, and the reviews are high quality, without industry funding then the thinking around supplementation may change. But if you’re healthy, and not a female trying to fall pregnant or sexually active and of reproductive age, eat a minimally processed, plant-based diet and you are going to be in good health!


* Cochrane Library Database – If you ever want a summary of the evidence on a topic that uses randomized controlled trials to test an intervention, then this is the place to look – and they now give great plain language summaries.


​Dr Nick Chartres is the Director of Science & Policy at the University of California, San Francisco working with the Program of Reproductive Health and the Environment. His work focuses on US federal chemical policy and regulation.

Nick received his PhD from The University of Sydney, where his thesis examined ways to reduce bias in public health guidelines, including the primary studies that are used in our national Dietary Guidelines. Nick also has a Masters in Nutrition.