Wednesday August 5 2015
Researchers studied the effects of capsaicin, found in chilli peppers
"Curry really could be the spice of life," says The Daily Telegraph, reporting on a study looking at the link between regularly eating foods that contain capsaicin – found in chilli peppers – and the risk of dying early.
The study of nearly 500,000 people in China found those who ate spicy food once a week or more were about 10% less likely to die during the seven-year follow-up period than people who ate spicy food less than once a week.
However, the researchers say their work cannot prove that spicy food was behind the lower chance of death, and their work in China should not be taken to mean the same would be true elsewhere in the world.
Where did the story come from?
The study was done by researchers from China (Peking University, the Chinese Academy of Medical Sciences, and five regional Centers for Disease Control and Prevention), the US (Harvard School of Public Health and Harvard Medical School), and the UK (the University of Oxford). It is part of the China Kadoorie Biobank study, an ongoing study of half a million adults from areas around China.
It was funded by grants from organisations including the National Natural Science Foundation of China, the Chinese Ministry of Science and Technology, the Wellcome Trust in the UK and the Kadoorie Charitable Foundation in Hong Kong.
The study was published in the peer-reviewed BMJ, and the research can be read for free on the BMJ website.
The story has been widely reported in the media, with newspapers such as the Mirror claiming that the research shows "curry helps you live longer" – but the study was carried out in China, so people were unlikely to have been eating curry.
The Mirror claims that, "people who ate spicy meals like curry favourites tikka masala, jalfrezi and vindaloo once or twice a week were less likely to die than those who had them less". The study did not look at consumption of Indian-style dishes such as vindaloo, but at how often Chinese people included chilli pepper or other spices in their diet.
What kind of research was this?
This prospective observational study aimed to find a link between regularly eating chilli or other spices and how long people lived.
Observational studies are good at finding possible links between factors such as diet and health. However, they cannot prove that one factor causes another.
What did the research involve?
Volunteers took a variety of tests and questionnaires relating to their health, family health, diet, exercise, income, tobacco and alcohol use, occupation and many other factors. They also answered a food frequency questionnaire, which asked how often they ate hot, spicy foods and what types of spices they used.
The researchers followed up the volunteers for an average of 7.2 years. They looked at whether people who eat chilli or other spices were more or less likely to have died during that time.
They adjusted their figures to take account of many factors we know affect length of life, such as smoking. They then calculated how likely people who ate spicy food regularly were to die, compared with people who ate spicy food less than once a week.
What were the basic results?
The researchers looked at data from 199,293 men and 288,082 women. During the study period, 11,820 men and 8,404 women died. Compared with people who ate spicy food less than once a week, people who ate spicy food on one or two days were 10% less likely to have died during the study (hazard ratio [HR] 0.9, 95% confidence interval [CI] 0.84 to 0.96).
People who ate spicy food more than two days a week were about 14% less likely to have died during the study (HR 0.86, 95% CI 0.8 to 0.92) but the difference between eating spicy food once or twice a week and more often was small enough that it might be down to chance.
People who ate food containing fresh chilli pepper more than six times a week were less likely to die than those who ate dried chillies this frequently.
The researchers looked at the causes of death and found people who ate spicy food more often were less likely to die from cancer, heart disease or respiratory (lung) diseases. However, the amount of spicy food made little difference to the chances of dying from stroke, diabetes or infections.
How did the researchers interpret the results?
The researchers said their results showed "significant inverse associations" between eating spicy food and dying of any cause or of some specific causes, meaning that people who ate spicy food were less likely to die of these causes.
They said the active ingredient in chilli pepper, capsaicin, has been shown to have a range of health-promoting effects, including antioxidant, anti-inflammatory and anti-cancer effects.
However, the researchers were cautious about their results. They said they could not conclude that spicy food protected against death, and that it is "essential" to carry out research in other groups of people outside China to be sure the results apply elsewhere.
They say further research could lead to evidence that will allow for updated guidelines on what people should eat for a healthy diet.
This large, well-designed observational study adds to the evidence that certain spices such as chilli pepper may have a beneficial effect on health. But this study does have limitations that need to be taken into account.
The study found that people in China who ate a diet that included spicy food (mainly from chilli peppers) at least once a week were less likely to die during the study period than those who ate spicy food less often. These results applied to men and women, even after taking account of factors that affect the risk of death, such as age.
The study is part of an ongoing investigation into the effect many factors have on human health, including diet.
The amount of data collected on individuals, including detailed information about their regular diet, activity levels, occupation, family health history and other factors, means the researchers have a better chance of finding an effect from specific factors in the diet.
Also, the size of the study means the researchers have enough data to show clear trends, with less likelihood the results are down to chance alone.
However, even with the amount of detail collected about people in the study, we cannot be sure other factors did not have an effect. For example, we don't know how people cooked the chilli peppers, so we don't know whether they may have used more or less cooking oil, or other spices, or ate more rice or other carbohydrates to "dampen down" the effect of the hot chilli.
Additionally, the diet frequency questionnaire was only completed once, at the beginning of the study, and people's diets can change over time.
The lifestyles of people in rural China are likely to be very different from the urban populations of the UK or US. Eating some of the same foods may not have the same results if lots of other things about your life are different. The type of spicy food eaten by people in China, with different cooking techniques, may be very different from the sort of spicy foods eaten in the UK.
The study also found that drinking alcohol may reduce any positive effects of eating chilli peppers. The link between reduced chances of death and eating spicy food was weaker in people who also drank alcohol. The habit of drinking beer with curry in the UK may undermine any good news on chilli pepper.
Overall, this study adds to emerging evidence that capsaicin in chilli pepper may have a positive effect. We now need to see studies in populations outside China to be sure the findings apply to the rest of the world.