Tomato extract's heart effects exaggerated
“Ketchup with everything: tomato sauce helps fight heart disease,” is the misleading headline in The Daily Telegraph.
The headline follows a small study conducted into lycopene tablets, which involved 36 people with cardiovascular disease and 36 healthy volunteers. Lycopene is the pigment that gives tomatoes (and some other fruit and veg) their distinctive colour. It has been the subject of numerous research projects in recent years, as it is thought to have antioxidant properties that may help protect against diseases that affect the heart and blood vessels (cardiovascular diseases).
This latest study found that people with cardiovascular disease who took statins saw their blood vessels dilate (widen) to a greater extent after they were treated with a chemical called acetylcholine if they had been taking lycopene every day for two months, rather than a placebo.
The lycopene tablet had no significant effect on any of the other outcomes the researchers looked at, and no effect on healthy volunteers (apart from increasing lycopene levels in the blood).
While improving the dilation of blood vessels may hypothetically reduce the risk of cardiovascular disease, this remains unproven in a real life setting.
Larger, longer-term studies are required to determine whether taking lycopene actually cuts the risk of heart attack and stroke.
Where did the story come from?
The study was carried out by researchers from the University of Cambridge and Cambridge University Hospitals NHS Foundation trust in the UK, and the University of Tartu, in Estonia. Funding was provided by Cambridge University Hospitals NHS Foundation Trust. The individual researchers were funded by the Wellcome Trust, the British Heart Foundation, the Estonian Science Foundation, the European Union Social Fund and the National Institute of Health Research Cambridge Comprehensive Biomedical Research Centre.
The study was published in the peer-reviewed, open-access journal PLOS One and can be read for free online.
Misleading headlines aside, the media have reported the story accurately and highlighted that larger studies are required to determine whether the effects shown here will have real health benefits.
What kind of research was this?
This was a randomised controlled trial (RCT) that aimed to investigate the effects of lycopene, the red pigment found in tomatoes (and certain other fruits and vegetables), on the blood vessels of patients with cardiovascular disease who were taking statins, as well as on healthy volunteers.
Previous research has found a link between reduced cardiovascular disease and the “Mediterranean diet”; the researchers wanted to see if this could be, at least partially, due to lycopene.
RCTs are the best way of demonstrating a cause-and-effect relationship. However, this was a small-scale trial, and the findings need to be replicated in a larger group of people.
What did the research involve?
The researchers randomised 36 patients with cardiovascular disease who were taking statins to either 7mg lycopene or a placebo daily for a two-month period.
The researchers then looked at the responses of blood vessels in the arm to acetylcholine – a chemical that causes them to dilate.
They also looked at the responses of blood vessels to other chemicals that cause them to dilate or contract, arterial stiffness, blood pressure, levels of different markers in the blood, as well as safety and tolerability.
The researchers then repeated these tests with 36 healthy volunteers.
What were the basic results?
Among the patients with cardiovascular disease who were randomised to take lycopene, dilation after acetylcholine improved by 53% and was significantly different to dilation in patients with cardiovascular disease who were randomised to take placebo.
There were no differences in the response of blood vessels to other chemicals, in arterial stiffness, blood pressure or the levels of different markers in the blood, apart from lypocene levels.
Lycopene had no effect in healthy volunteers on any of the outcomes investigated, apart from levels of lycopene in the blood.
How did the researchers interpret the results?
The researchers concluded that “despite optimal secondary prevention medication, endothelial function [the function of the cells that line blood vessels] is impaired in patients with cardiovascular disease, and this is improved by oral supplementation with 7 mg lycopene, without any concomitant changes in traditional risk factors such as [blood pressure] or lipid profiles, or measures of inflammation. In contrast, we were unable to demonstrate any changes in endothelial function or other parameters after lycopene treatment in [healthy volunteers].”
Conclusion
This study found that the blood vessels in people with cardiovascular disease who were taking statins dilated more after they were treated with a chemical called acetylcholine if they had been taking lycopene every day for two months, compared to those taking placebo pills.
The lycopene tablet had no significant effect on any of the other outcomes the researchers looked at, and no effect in healthy volunteers, although it did increase lycopene levels in the blood.
Although impaired endothelial function is a known predictor of future heart disease, this is, at best, a surrogate outcome. It is no substitute for following up people over time to see if improvement in endothelial function actually does translate into reduced deaths from heart attacks and stroke.
Due to this limitation, much larger RCTs, with a follow-up period measured in years rather than months, are required to determine whether taking lycopene actually cuts the risk of cardiovascular disease.
