"Glucosamine supplements 'may cut heart risk'," reports BBC News.
Researchers analysed the diet and lifestyle of almost half a million adults aged 40 to 69 in the UK, and followed them up for an average of 7 years.
They found people who regularly took glucosamine, a food supplement taken to reduce symptoms of joint pain and stiffness, were about 15% less likely to develop heart disease or have a stroke.
Some people take glucosamine for joint pain, but it's no longer prescribed for this on the NHS because there's a lack of evidence that it works.
The researchers said it may reduce inflammation, which is one factor in the development of heart disease.
This was an observational study, which means we do not know for sure that glucosamine was the reason why fewer people taking it had heart disease or stroke.
It could be, for example, that people who take food supplements live healthier lifestyles in general.
Where did the story come from?
The researchers who did this study were from Tulane University in the US.
It was funded by the US National Institutes of Health and published in the British Medical Journal. The study is free to read online.
The study was covered with enthusiasm by the UK media. Several reports said glucosamine cut the risk of a fatal heart attack or stroke by a fifth.
While the figure is correct (relative risk of a fatal heart attack or stroke is 22% lower), it represents an absolute risk difference of less than 1%, from 0.7% of people to 0.5% of people dying. And we do not know whether glucosamine is the reason for the lower risk.
Most of the news stories included comments from experts advising that people focus on a healthy lifestyle rather than taking dietary supplements.
What kind of research was this?
This cohort study used data from the ongoing UK Biobank study.
Cohort studies are good ways to spot patterns between different factors, in this case glucosamine use and cardiovascular disease.
But they cannot tell us if one factor (glucosamine) causes another (lower risk of cardiovascular disease). Other factors may be involved.
What did the research involve?
The UK Biobank study enrolled 500,000 adult volunteers across the UK and took a mass of data about them, including lifestyle and dietary questionnaires, fitness tests and DNA tests.
People in the study are followed up through mortality and medical records, and questionnaires.
The researchers used data on 466,039 people who did not have cardiovascular disease at the start of the study and had answered questions about their use of glucosamine.
They were followed up for 7 years.
Researchers used the data to find out whether people who took glucosamine were more or less likely to have a heart attack or stroke, or die from a heart attack or stroke.
They took account of a wide range of potential confounding factors, including:
- age, gender and race
- household income
- smoking and alcohol intake
- body mass index
- physical activity levels
- healthy diet
- whether they had diabetes, high cholesterol or high blood pressure and were on treatment
- whether they took other vitamin, mineral or food supplements
What were the basic results?
Almost 20% of the people in the study (aged 40 to 69) took glucosamine.
People who took the supplement were more likely to be women, older, non-smokers, more physically active, eat healthier diets and take other supplements.
During the 7 years of follow-up, 10,204 people had a heart attack or stroke (2.2%).
- 2.2% of people who did not use glucosamine had a heart attack or stroke
- 2.0% of people who did use glucosamine had a heart attack or stroke
- after taking account of possible confounding factors, people who took glucosamine were 15% less likely to have had a heart attack or stroke (hazard ratio [HR] 0.85, 95% confidence interval [CI] 0.80 to 0.90)
- 0.7% of people who did not use glucosamine died from a heart attack or stroke
- 0.5% of people who did use glucosamine died from a heart attack or stroke
- after taking account of possible confounding factors, this represented a 22% reduced risk of dying from a heart attack or stroke (HR 0.78, 95% CI 0.7 to 0.87) for people who took glucosamine
How did the researchers interpret the results?
The researchers said: "Habitual use of glucosamine supplement to relieve osteoarthritis pain might also be related to lower risks of CVD [cardiovascular disease] events. Further clinical trials are needed to test this hypothesis."
Headlines suggesting that a supplement can "slash" your risk of heart disease or stroke are attractive, but the study does not back up the headlines.
This type of study cannot prove that one factor (glucosamine) is the cause of the results they found.
While the researchers tried to take account of other possible causes of the results, they could not account for everything.
The study did not collect information about how long people had taken glucosamine, what dose they were taking or how often they took it, and did not check whether people carried on taking it after the start of the study.
It's also worth bearing in mind that the actual change in risk – even if it was caused by glucosamine – is quite small.
A 15% drop in risk is smaller than the drop you'd see if you gave up smoking, for example. Smoking increases the risk of getting heart disease by 24%.
As one of the experts quoted in the press today says, if you want to reduce your risk of having a heart attack or stroke, it would be much better to concentrate on living a healthy lifestyle, rather than paying for glucosamine supplements.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The Daily Telegraph, 14 May 2019
The Daily Mail, 14 May 2019
The Sun, 15 May 2019
BBC News, 15 May 2019
Links to the science
The BMJ. Published May 14 2019