Wednesday August 4 2010
The study looked at the effects of capsaicin in rodents, not humans
“Curry could save your life,” reports the Daily Star. It said that “chilli-laden dishes such as vindaloo or phall might appear to cause the brave eater to tense up, but they make blood vessels relax”.This “lowers blood pressure, reducing the risk of deadly heart attacks”.
Contrary to the impression created by this news, the study in question only looked at the effects of capsaicin (the chemical that makes chillies hot) on the blood vessels of rats and mice, not humans. No investigation was made of humans eating chillies and their risk of high blood pressure, heart disease or death.
There has been some research into the medical properties of capsaicin in humans, including whether it can be used as a pain-relieving ingredient for use on the skin. Studies in humans will be needed before we can say whether long-term ingestion of capsaicin reduces blood pressure in humans. Until then, people with high blood pressure should not try substituting their blood pressure medication with a diet high in chillies.
Where did the story come from?
The study was carried out by researchers from the Chongqing Institute of Hypertension and other research institutions in China and Germany. It was funded by the National Natural Science Foundation of China, the National Basic Research Program of China, HKGRF, CUHK and the Ministry of Education in China. The study was published in the peer-reviewed scientific journal: Cell Metabolism.
The Daily Mirror, Daily Star and Independent cover this story. The Mirror does not tell readers that the study was in rats and therefore may not apply to humans. The Star notes that the study was in rats but says that the findings have been “mirrored in humans”, despite the fact that this study did not assess the effects of chillies in humans. The Independent provides a good account of the study, and notes that “the study on rats now needs to be confirmed by analysing any epidemiological association between eating chilli peppers and blood pressure”.
What kind of research was this?
This animal research looked at the effects of capsaicin on blood vessels and blood pressure in rats and mice. Capsaicin is the chemical that gives chillies their hot sensation, and it does this by binding to a protein called TRPV1 on the surface of our cells. The researchers say that laboratory research has shown that blood vessels relax when exposed to capsaicin. However, other studies in humans and rodents have had contrasting results, with some finding it raised arterial blood pressure while others found it lowered blood pressure. The researchers were interested in looking at the effects of dietary capsaicin on TRPV1 and blood pressure in rats and mice.
Animal research helps us to understand more about how bodies function normally and when experiencing disease. It gives researchers an insight into the ways in which disease might be treated. However, there are differences between animal species, which mean that findings in rats and mice may not necessarily apply to humans. Therefore, any findings need to be replicated in humans if possible. This research suggests that chemicals targeting TRPV1 may be able to reduce blood pressure, but more research to identify possible candidate chemicals and test them in animals and humans will be needed.
What did the research involve?
The researchers first looked at whether the TRPV1 protein was present on the cells that line blood vessels (endothelial cells). They then carried out several experiments to look at the effects of capsaicin on the blood vessels of mice. These experiments were carried out in both normal mice and mice that were genetically engineered to lack the TRPV1 protein. They also fed normal (“wild type”) mice either a diet that incorporated 0.01% of capsaicin or a diet with no capsaicin for six months and looked at the effect on their blood vessels.
Finally, they carried out similar experiments in a strain of rats with high blood pressure. They fed these rats either a diet including 0.02% capsaicin or a normal diet for seven months and looked at the effect on their blood pressure.
What were the basic results?
The researchers confirmed that the cells of blood vessels produce the TRPV1 protein, and therefore should be able to respond to capsaicin. They found that arteries from normal mice relaxed in response to being treated with capsaicin, but that arteries from mice genetically engineered to lack the TRPV1 protein did not. This showed that TRPV1 had to be present for capsaicin to have its effect.
Arteries from normal mice given a diet with capsaicin for six months relaxed more in response to a chemical that causes blood vessel relaxation than mice given a diet without capsaicin.
The experiments in rats with high blood pressure showed that capsaicin did not have an effect on their blood pressure after three weeks. However, blood pressure did start to fall after four months of the capsaicin diet, and this difference reached statistical significance between five and seven months.
How did the researchers interpret the results?
The researchers concluded that dietary capsaicin activates TRPV1 and that this improves the function of the cells lining the walls of blood vessels (endothelial cells). They suggest that TRPV1 may be a good target for drugs aimed at reducing high blood pressure, and that eating capsaicin in the diet could be a promising lifestyle intervention for helping people with high blood pressure.
This study found that in rats with high blood pressure eating a diet containing capsaicin over a period of months reduced their blood pressure. At this stage, it is not possible to say whether a similar effect would be seen in humans. The researchers report that another study has found that eating hot chillies causes a temporary increase in blood pressure in humans, but that the longer-term effects are not known. Until more research is done, people with high blood pressure should not try substituting their blood pressure medication with chillies.