The study comes one year after cured and processed meats were added to the list of cancer-causing agents by the World Health Organisation’s (WHO) cancer research agency IARC.
Using data from 971 subjects of France’s Epidemiological study on the Genetics and Environment of Asthma (EGEA), 42% of whom had asthma, the researchers reported a positive direct effect of cured meat intake on worsening asthma symptoms for 20% of the total participants over seven years.
The proportion of individuals with worsening asthma symptoms was 22% among those who had the highest intake of cured meat respectively, compared with 20% for
a medium intake and 14% for the lowest.
Using three types of typical French cured meat - ham, sausage and dried, cured sausage - the researchers defined a high intake as more than four servings of cured meat per week. One serving was defined as either two slices of ham; one sausage; or two slices of dried, cured sausage.
“The EGEA results are in agreement with previous research indicating a harmful association between cured meat intake and different measures of lung health in several countries, where the types and preparation of cured meats may be different,” they write.
Speaking for the Meat Advisory Panel, a group funded by the British meat industry, Dr Emma Derbyshire said: "It should be considered that this is just one study, so others ideally in the form of randomised controlled trials are needed. In this type of observational study cause and effect relationships cannot be easily determined as many different dietary and lifestyle factors can skew study findings."
Head of Research at Asthma UK Dr Erika Kennington said that although certain foods act as triggers for allergies in some people, there is no specific dietary advice to manage asthma symptoms generally.
“For most people with asthma, healthy eating advice is exactly the same as it is for everyone else: follow a balanced diet that includes plenty of fresh and unprocessed food and is low in sugar, salt and saturated fat," she said.
Novel method
The researchers from France's National Institute for Health and Medical Research (INSERM) write that this is the first prospective study on the association between cured meat intake and asthma symptoms, and is also the first to use a novel method - a counterfactual approach to mediation analysis - to estimate the role of obesity (determined using Body Mass Index - BMI) as a mediator rather than confounder.
This is important, they write, because obesity is a likely risk factor for the incidence and exacerbation of asthma, and so one of the challenges when investigating the association between diet and asthma is to properly account for BMI.
Scores were also adjusted for different dietary patterns. "We acknowledge that findings might not be generalisable to populations with completely different diet habits, such as infrequent cured meat intake and very different food consumptions," they write.
The study
Data from 971 individuals with a mean age of 43 years was used. Just under half (49%) were men and 42% had asthma.
Subjects’ cured meat intake was categorised into three exposure levels. 19% ate one portion per week; 48% had a medium consumption with 1-3.9 servings per week and 33% had a high intake with more than four servings per week.
The group with the lowest intake (one portion per week) was considered to be ‘non-exposed’ and was taken as the reference group. They acknowledge that their definition of this non-exposure group was “not ideal” but said there was a limited number of participants who did not eat cured meat at all which would have resulted in problems during the statistical analysis.
They point to previous research that has identified the use of nitrites in cured meat, which may lead to nitrosative stress - and oxidative stress-related lung damage and asthma. C-reactive protein could also increase systemic inflammation which impacts asthma. The high salt and saturated fat content in cured meat has also been associated with asthma, although evidence for this has mainly been for childhood-onset asthma.
Asthma symptoms were measured using the asthma symptom score, which asks individuals to rate symptoms such as breathlessness, feelings of a tight chest and attacks of short breath at rest or during exercise on a scale of one to five.
The highest cured meat eaters tended to be younger, more likely to be men, smokers, to report a higher total energy intake and to have suffered from asthma. They also had a higher intake of sodium and saturated fat.
Source: Thorax Journal
First published on 20 December 2016, doi 10.1136/thoraxjnl-2016-208375
“Cured meat intake is associated with worsening asthma symptoms”
Authors: Zhen Li, Marta Rava, Annabelle Bédard, Orianne Dumas, Judith Garcia-Aymerich et al.