Lots of people take glucosamine to help them with pains in their joints, but is there hard evidence that it improves things, asks Dr Chris van Tulleken.
Of all the supplements on the shelves purporting to aid one part of our body or another, the most popular by a long way are those that are supposed to help our joints - and most of those contain glucosamine.
In 2014 the world bought over 29,000 tons of the stuff. Pretty impressive considering its benefits in clinical trials remain controversial. So what's going on? Why do so many people swear by it?
Glucosamine is certainly important in our bodies - it's one of the building blocks of cartilage, ligaments and tendons - all possible causes of pain in a creaky joint. The theory is, then, that supplying our bodies with more of this building block might give it what it needs to make repairs. Since glucosamine is also one of the building blocks of chitin - the material that makes up the shells of crustaceans and shellfish - they are (unfortunately for them) a convenient source for the supplement industry (vegetarian options come from mushrooms or processed grains).
When it comes to the evidence that popping prawn pills can help our joints, though, things get fishy. Usually the problem with supplement pills is lack of studies - there simply isn't enough funding available for large-scale independent trials. Not so with glucosamine.
With such a massive global market, there's plenty of money being made by big companies - and that's problem number one. Commercially funded trials of products are a well-known issue in medicine, and in the case of glucosamine studies it seems that those that are commercially funded turn out to be more likely to show a positive result than those done independently.
Even putting aside industry-funded studies, though, there have been a lot of decent trials done on various forms of glucosamine compared with pretty much anything you might consider an alternative - painkillers, exercise, other drugs... and placebo.
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- Chris van Tulleken is one of the presenters of Trust Me, I'm A Doctor, broadcast on Thursdays at 20:00 BST on BBC Two - catch up on BBC iPlayer
And yet, although one study might give a positive result for glucosamine one year, another gives a negative the next. Every few years someone does a review of all the research published so far and these reviews also seem to alternate between "slight advantage glucosamine" and "no advantage glucosamine" in the tests against placebo.
It's like a tennis match between two very closely-matched players. And that, to my mind, is an analogy that explains what might be going on here. Could it be that "placebo" is actually a decent player in the fight against joint pain?
We often think of "placebo" in these sorts of trials as meaning "nothing". We test sugar pills against things like turmeric in a study and show that the sugar pill has no effect. But in the case of pain, placebo is something quite different.
Hence we set out on Trust Me, I'm a Doctor to do a joint pain study with a difference. There was no point us setting out to add just one more small study to the plethora already looking at glucosamine. We wanted to do something that would be of most use to all of us who are faced with a painful joint and want to know the most effective, and cost-effective, way to make it better.
In collaboration with Prof Phil Conaghan of the University of Leeds, a world expert on joint pain, we recruited 80 people with painful knees. Phil and his team assessed their joints and asked them to rate their pain levels, and then 40 of them were given a "supplement pill" to take daily and the other 40 were given daily exercises. After two months, we asked them to rate their pain again. And the results were very telling.
In the group that took the supplement pill, 55% reported a significant reduction in pain - an improvement of around 30% or more. In fact, many in the group were extremely enthusiastic about the effect this supplement had, one saying she felt "like a new person".
In the group that were given exercises to do, 80% reported the same reduction in pain. So, the exercises were much more effective than the supplement - but the supplement was still very good at reducing our volunteers' pain.
So what was this marvellous pill? As you've probably already guessed by now, it was just a placebo. Placebo works very well for joint pain. Glucosamine "works" - but the evidence is that it doesn't work much better than placebo.
If you've got sore joints, then, you might as well save yourself some money - about half the time a sugar pill will make you feel better, but if you actually want the best chance of making a difference, then Phil's exercises are the way to go. Nothing beats them in studies - and they're free.
As Phil explains: "A lot of the pain is coming from the tendons and structures around the joint. If you have trouble getting out of a chair, or trouble undoing a jar, you're at risk of joint pain because your muscles are weak."
The exercises strengthen those muscles and take the strain off your joints. No need to crush up more crustaceans in our attempts to get supple again.