August 4, 2015

expert reaction to study investigating consumption of spicy food and risk of death

Writing in the BMJ, a group of researchers have published their work into possible associations between consumption of spicy food and mortality in a Chinese population, reporting that those who regularly ate spicy food had a lower risk of death.

Prof. Ian Rowland, Emeritus Professor of Human Nutrition, University of Reading, said:

“Spices and herbs are extensively used throughout the world for culinary purposes and also are used in many cultures for medicinal purposes. Their potential health benefits are being increasingly investigated in experimental studies in cell cultures, animals and human subjects, but data from large scale population studies of disease specific mortality, such as the one described in this paper, are lacking.

“This is an interesting epidemiological study that suggests that regular consumption of spicy foods, namely chilli spices, may reduce overall mortality in the Chinese population. The relative risk reduction in those consuming chilli 6 or 7 days a week compared with those eating spicy foods less than once a week was 14%.

“The strengths of the study are that it is very large – about 500,000 people were recruited with approximately 20,000 deaths recorded over the observation period. The authors also looked at deaths from specific causes and found reductions in risk for deaths from respiratory disease and heart disease, with less consistent effects for cancer and no significant effects on deaths from stroke, infections and diabetes.

“As with all epidemiological studies, it is important to remember that this study only provides information on associations of spicy food intake and mortality and does not show that spices actually cause the reduction in risk. Also there are a number of limitations in the study, the main one being the poor dietary information that was collected. This was obtained by a qualitative, unvalidated food frequency questionnaire, which makes it difficult to adjust for  potential dietary confounding  factors, although the authors did make some adjustment for  body weight, alcohol, smoking, physical activity, frequency of consumption of meat and vegetables. Although the paper talks about ‘spicy food consumption’ the data on spice intake is limited to various types of chilli and is based on frequency of intake rather than amounts consumed.

“Despite these limitations, the study presents some intriguing findings and hopefully will stimulate further studies in other populations and incorporate a broader spectrum of spices and herbs in the analyses.”

Dr Amelia Lake, Lecturer in Knowledge Exchange in Public Health, Durham University, said:

“While this is an interesting study and headlines might suggest the birth of a new ‘superfood’, it’s time to step back and acknowledge the limitations of this study.  The study tells us about the participants’ spicy food consumption but lacks details about the rest of their dietary intake.  There may also have been other protective factors different from but associated with the spicy food intake that were not measured.  Additionally the study doesn’t tell us about the participants’ long term consumption of these spicy foods.  Therefore there are gaps in the information and we shouldn’t jump to conclusions.

“While there is some evidence that this broad group of foods called spices may have some beneficial effects, the take-home message is to carry on with a balanced, varied diet where a bit of spice may have some benefits.”

Ms Catherine Collins, Principal Dietitian at St George’s Hospital NHS Trust, St George’s University Hospital Foundation Trust, said:

“The Mediterranean style approach with its emphasis on a varied diet rich in plant-based foods epitomises our healthy eating blueprint, and the use of herbs and spices is common in such diets.  We know from food analysis that herbs and spices punch above their weight in contributing powerful anti-oxidant substances to the diet. Whether freshly chopped or dried, their small size and large surface area allows our digestive tract to extract a large proportion of their potentially beneficial substances. Of course, whether we can use what plants provide us with is a different story. Just because a herb or spice is rich in antioxidants and other biologically useful substances doesn’t necessarily mean it’s as useful to us in our body. We may not be able to use the substance provided or we may ‘saturate’ our need for that substance at relatively low intake, so more doesn’t necessarily mean ‘better’. We know that herbs and spices interact with substances in other foods eaten at the same time, and that in ‘cooking from scratch’ you may choose a selection of spices in differing amounts, which would have different effects biologically.

“So this study is interesting in that it appears to show that in a large group of middle aged Chinese people, recruited in 2004, who enjoyed spicy food more than a few times a week lived longer than those who didn’t. For any amount of spicy food intake from chilli peppers (fresh or dried) overall mortality was reduced 14% at a median 7 year follow-up compared to those who never ate spicy foods. There was also a sex-related difference in effect. For men, spicy food consumption was only associated with reduced mortality from respiratory diseases. Death from all other specific causes examined was not significantly different. For women, a spicier diet was associated with reduced risk of death from cancer and heart disease. It is more useful to examine specific mortality causes rather than ‘all cause mortality’ as the latter includes accidents, suicide etc. where diet has no impact at all.

“Like many large population studies, there’s a number of caveats to this study which can’t be ignored. First, it was a study of Chinese people, who have different diet and lifestyles to us in the West. Secondly, the study relied on dietary data of spicy food intake reported only once, when people were initially recruited to the study in 2004. Many older people find they’re less tolerant of spicy, ‘hot’ foods as they get older. Despite age-related changes in food preferences, data adjusted for age continued to show a reduction in deaths from heart disease (reduced 25%), diabetes (by half), respiratory disease (by 40%) and infections (by 30%) in those taking spicy foods daily at recruitment.

“It’s rare in any style of cooking for just one spice to be used, so it’s impossible to determine whether chilli peppers have some magical effect on mortality (highly unlikely) or that using chilli represents a style of eating that adds health as well as nutritional benefits. Although the authors make a small attempt at qualifying the rest of the diet (demonstrating that red meat, fruit and vegetable intakes were similar across all groups), they haven’t addressed other key factors influencing nutritional intake – for example actual amount of alcohol consumed, oily fish intake, or vegetable protein sources such as soy, which features large in the Asian diet. All these factors would have influenced mortality risk.

“When the authors adjusted for all known diet and lifestyle factors influencing mortality, consuming spicy foods even once or twice a week was associated with a trend to lower mortality risk, but this proved only statistically significant for death from respiratory diseases. This is an interesting study, but not sufficiently persuasive to make me recommend chilli peppers should form part of our daily diet.”

Prof. Kevin McConway, Professor of Applied Statistics, The Open University, said:

“This is a large and competently performed study, but it demonstrates very clearly how difficult it is to sort out what is causing what from an observational study. I’d suggest that anyone preparing a story on this should be sure to read the accompanying editorial by Nita Forouhi, which clarifies very clearly how we should interpret the findings.

“The authors of the main study make it very explicit that no definite conclusions can be drawn about cause and effect, and that they are simply calling for further research. As Forouhi says in her editorial, “Their findings should be considered hypothesis generating, not definitive.” That is, they suggest that it might be useful to look further and in more detail at possible health effects of eating chillies, and carefully do not suggest anyone should change their diet on the basis of this work.

“The researchers themselves point out various ways in which it’s hard to tell what causes what. The issue is that, if people who eat spicy food more often have lower death rates, that might indeed be caused by the chilli eating, or it might be caused by something different that is related to eating chillies and also, separately, happens to promote health. Maybe this is something in the way spices are used in Chinese cooking, or related to other things people eat or drink with the spicy food. Maybe it has something to do with the sort of people, in China, who tend to eat more spicy food. For instance, it’s interesting that the people in the study who ate spicy food almost every day were very much more likely to live in rural areas than were the other participants. In their statistical analysis, the researchers allowed for some of the possible confounding factors that might work in this way, but they can’t allow for everything. The researchers also point out that it’s possible that cause and effect are working the other way to some extent – that is, that people with long-term illnesses may be less likely to eat spicy food and also, separately, more likely to die during the study.

“Further, the study can’t tell us anything direct about the effect of spicy food in other populations. The Chinese population that they studied is different from the population in Britain, in terms of cooking practices, social relations, health care systems, genetics, and a lot else.

“So should we change our diet in the light of this research? The researchers don’t suggest that, and nor does Nita Forouhi in her editorial, where she writes, “Should people eat spicy food? It is too early to say, but the debate and the research interest are certainly hotting up.” I’d agree. And it’s important to realise that the study gives very little encouragement for the stereotypical English pastime of going out for several pints of beer and a hot curry. The relationship between eating spicy food and a lower death rate was apparent really only in people who didn’t drink alcohol at all.”

‘Consumption of spicy foods and total and cause specific mortality: population based cohort study’ by Jun Lv et al. published in the BMJ on Tuesday 4 August 2015. 

Declared interests

Prof. Ian Rowland: “I am on the Scientific Advisory Board of the McCormick Science Institute, which focuses on investigating the evidence for health benefits of  herbs and spices – McCormick’s, which provides the funding for the Institute, is a big herb and spice producer in the USA (and own Schwarz in the UK).”  Prof Rowland is also Editor-in Chief of the European Journal of Nutrition.

Dr Amelia Lake:

– paid employment or self-employment: Lecturer at Durham University and honorary Research Fellow at Newcastle University.  I have an inactive nutrition consultancy called Lake Nutrition.

– grant funding: NIHR SPHR & Children’s Foundation, MRC via Fuse The Centre for Translational Research in Public Health.

– voluntary appointments: British Nutrition Foundation Scientific Advisory Board.

– memberships: BDA, Nutrition Society, Association for Nutritionists, Association for the Study of Obesity.

– decision-making positions: The Responsibility Deal High Level Steering Committee (representing the British Dietetic Association)

– other financial interest: N/A.

Ms Catherine Collins and Prof. Kevin McConway declare no interests.