Whenever I see an article entitled “The science of … ” I become suspicious. So when the Guardian's G2 section published a piece last week called "The science behind dietary supplements" by Spencer Nadolsky of nutrition website examine.com, it rang alarm bells.



As it did for many others. Commenter flash131 discovered that Nadolsky appeared to be registered as a co-director of Leaner Living, which sells diet supplements. Subsequently, examine.com told the Guardian that he no longer has any connection to the company he co-founded, which is now run by his brother. However, during his time at Leaner Living Nadolsky received a warning from the Federal Drug Administration for making therapeutic claims for a product that hadn't received FDA approval.



It is also worth noting that every page of examine.com promotes a $49 guide to dietary supplements.

The Guardian's article links to the relevant sections on examine.com, where there are over 700 PubMed references citing evidence. It's true that PubMed is a great search hub, but it is hardly an endorsement for dietary advice. It is an index of every paper published in life science journals and eBooks, and with 22 million citations listed, the scientific quality varies.

So how do you know whether a scientific paper can be trusted? The first thing to look into is whether it has been peer-reviewed. Most content indexed on PubMed, though not all, will have been. Better still, look out for systematic reviews, which try to summarise everything that has been published on a particular topic. Best of all are meta-analyses, which take all the information from studies found in a systematic review and crunch the data in an attempt to give a definitive result.

A document on supplements from NHS Choices notes that most articles about science in the media fail to mention that some forms of evidence are more reliable than others. We are not aways told that a systematic review is better than an individual study, for example, or that a meta-analysis is the gold standard.



So as Nadolsky says in his article, let's “tune out the hype and see what the evidence has to say”.

Under the heading “do you need it?” in the section on glucosamine, Nadolsky recommends a daily dose of glucosamine sulfate of at least 1,500mg a day for osteoarthritis. Yet despite being the third biggest-selling supplement in 2009 with sales of £68m in the UK, glucosamine has no proven effect on osteoarthritis and is not recommended by the National Institute for Health and Care Excellence, which produces guidelines on treatment for the NHS after reviewing the best research. Nice says there is insufficient evidence to support the use of glucosamine in osteoarthritis and recommends that it should not be funded by the NHS. A systematic review published in the BMJ found that the supplement did not reduce pain or have any effect on the narrowing of the "joint space", which is a characteristic of the disease.

So why does Nadolsky assume it's all good and recommend a dose? Even his own website advises that the effect appears small.

In the section on protein, Nadolsky – a keen body builder – tells us that "slowly but surely, protein powders have become a common part of a regular diet" and that they “are the most easily ingested and convenient form of protein”.

It's true that in 2010 protein powder sales hit £200m in the UK, but is there any need for them? The recommended daily amount of protein for 19-50 year olds is 55.5g for men and 45g for women. But according to the British Nutrition Foundation, average protein intake is 88g for men and 64g for women.

Taking a protein supplement may not only be unnecessary, it could be harmful. In 2010, a Consumer Reports survey of 15 brands in the USfound that some protein drinks were contaminated with heavy metals that could reach harmful levels in the recommended three daily servings. Because protein supplements are not categorised as medicines, quality control during their manufacture is perhaps not as rigorous as it might be. Furthermore, the NHS warns that excessive protein intake can lead to bone demineralisation and osteoporosis. And a recent article in the journal Cell linked high intakes of animal protein to cancer and higher overall mortality in the under 65s.

Given that most of us already eat more than the recommended daily amount of protein, why consume protein powders at all?



Nadolsky recommends taking multivitamins "if you pay no attention to your diet or are always dieting", implying that the pills would help compensate for a poor diet. In fact, multivitamins might make things worse. A recent meta-analysis found no evidence that the antioxidants beta-carotene, vitamins A, C, E and selenium prevent disease. Beta-carotene and vitamin E actually increased mortality, as did high doses of vitamin A.

Worryingly, Nadolsky also advises 50 micrograms (2,000 IU) of vitamin D per day, which is twice the NHS recommended maximum intake of 25 micrograms. The recommended daily allowance is only 5 micrograms, though advice varies between countries. Taking too much vitamin D for a long time can cause calcium buildup, damaging the kidneys and even softening bones, and while we need extra at particular stages of life – particularly during pregnancy and breastfeeding and for those aged over 65 – most of us get enough from our food and what we synthesise for ourselves with the help of sunlight.



In summary, you probably shouldn't consider taking supplements unless advised to by your GP. NHS Choices also offers great advice, and the Cochrane Collaboration is an independent body that provides open learning tools to help you put the media hype surrounding diet and nutrition into perspective.

The real science of dietary supplements shows that very few of us need them and most of us will do just fine by eating a healthy, balanced diet.