Monday January 16 2017
Chilli peppers have been claimed to have antioxidant effects
"How hot chilli could help you live longer," the Daily Mail reports. A US study found that people who reported eating red hot chilli peppers had around a 13% reduced risk of premature death compared to those who avoided them.
The study looked at adults in the 1980s and 90s who reported eating any hot chillies over the past month – which could range from a single chilli to several chillies every day.
There were no significant links found when drilling down to specific cause of death rather than just overall mortality.
Ultimately this study proves very little. The researchers attempted to account for possible contributory factors, such as other dietary factors, income and age, but as they admit, unmeasured health and lifestyle factors could be influencing the link.
It is plausible that hot chillies could be linked beneficial effects. There is some evidence that the active ingredient in red hot chilli peppers, (the food, not the band) capsicum may have anti-inflammatory or anti-oxidant effects, while also boosting the metabolism. But with the exception of one study in China (which we analysed in 2015) the research has involved rodents.
It is always unwise to rely on a single "superfood", such as assuming that chillies could be the spice of a long life. It is better to follow standard recommendations and eat a balanced diet high in a variety of fruit and vegetables, limit salt, sugar and saturated fat – stay active, avoid smoking and moderate your consumption of alcohol.
Where did the story come from?
The study was carried out by two researchers from University of Vermont College of Medicine in the US. The authors report receiving no funding for their study and declare no conflict of interest. The study is published in the peer-reviewed journal PLOS ONE, an online open-access journal so the study is free to read online.
The Mail's coverage rather takes these findings at face value. This study does not prove that eating hot chillies will help you live longer.
What kind of research was this?
This was a cohort study which aimed to see whether consumption of hot chilli peppers was linked with mortality.
The researchers say that evidence on the health effects of spice consumption is lacking, particularly from Western populations. Therefore they aimed to investigate this using a large cohort of US citizens. The difficulty is that observational studies can never prove cause and effect between single dietary factors and health outcomes. Many other factors may be confounding any link. Self-assessments of frequency and quantity of consumption of individual food items can also commonly be subject to recall bias.
What did the researchers do?
The research used data from the National Health and Nutritional Examination Survey version III (NHANES III). Data was collected between 1988 and 1994 and the participants were at least 18 years old and said to be representative of the US adult population.
Survey participants took part in interviews assessing their health, lifestyle and socioeconomic factors. As part of this they completed an 81-item food frequency questionnaire assessing usual consumption of food and drink items over the past month.
Hot red chilli pepper consumption per month was assessed from responses to the question "How often did you have hot red chili peppers? Do not count ground red chili peppers." The researchers considered any response other than no chillies per month as a chilli consumer.
The researchers followed up mortality (by cause) by linking with the National Death Index to end of 2011. In their analyses between mortality and chilli pepper consumption the researchers adjusted for these confounders:
- age, gender and ethnicity
- marital status
- educational level, employment and annual income
- physical activity
- consumption of meats, vegetables and fruits
What did they find?
A total of 16,179 adults had complete data for analysis.
Various factors were linked with increased chilli consumption, for example being younger, male, white, Mexican-American, being a smoker and drinking alcohol, and consuming more meat and other vegetables.
During an average follow-up of 18.9 years there were 4,946 deaths – 21.6% of the chilli consumers died compared with 33.6% of the non-consumers.
In the model adjusted for all confounding variables, any level of chilli consumption was linked with a 13% reduced risk of dying during follow-up (hazard ratio [HR] 0.87, 95% confidence interval [CI] 0.77 to 0.97).
When looking by specific cause of death, however, no significant links were found between chilli consumption and any cause of death.
What did the researchers conclude?
The researchers conclude: "In this large population based prospective study, the consumption of hot red chili pepper was associated with reduced mortality. Hot red chili peppers may be a beneficial component of the diet."
The researchers conclude from their observational study that hot chillies may be beneficial to health.
However, there are several points to bear in mind:
- This is observational survey data that can't prove direct cause and effect. The researchers have made a valiant attempt in following the survey participants for mortality outcomes for almost 20 years, and tried to adjust for many different health and lifestyle factors that could be influencing the link. However, it is still likely that these adjustments have not been able to fully account for all of these factors – and there may be other unmeasured factors that are influencing the link.
- The analysis only looks at the very general link with any hot chilli consumption in the past month vs. none. It doesn't look at quantity or frequency of chilli consumption – or type of chilli for that matter. Therefore the "chilli consumers" could include anything from a person who included a single chilli in a curry over the past month, for example, to people who daily eat several of the hottest chillies. Therefore it doesn't give you a great deal to go on.
- No links were found with any particular cause of death – only the overall association with mortality that has compiled all deaths. This makes it more difficult to draw much meaning from the results. Even if chillies are directly influencing mortality, this study can't tell us by what mechanism they could be doing this.
- The study has only looked at a specific US population sample – and their chilli consumption was assessed over 20 years ago. They may not be representative of people today, of the US culture or others.
It is plausible that hot chillies could be linked with health effects – possibly similar to how flavonoids or pigments of other fruit and vegetables have been linked with anti-inflammatory or anti-oxidant effects – or it could be down to capsicum, the active ingredient in chillies. But this is just speculation – there's no good evidence around this.
Ultimately, rather than looking for a single "superfood" that will boost health and reduce mortality risk, you're probably better off just following the standard recommendations. Eat a balanced diet high in a variety of fruit and vegetables, limit salt, sugar and saturated fat – stay active, avoid smoking and moderate your consumption of alcohol.