Eating a lot of cured and processed meat such as ham and salami is linked to worsening asthma symptoms, according to research.
Four or more weekly servings - considered to be a high dietary intake - seems to have the greatest impact on symptoms, the findings published online in the journal Thorax suggest.
Cured and processed meat is rich in nitrites, which may have a role in airway inflammation - a typical feature of asthma.
To find out if dietary processed meat intake was associated with the worsening of asthma symptoms over time, and what role, if any, obesity might have, the researchers drew on data from participants in the French Epidemiological study on the Genetics and Environment of Asthma (EGEA).
It tracking the health, through surveys and medical examination, of more than 2,000 asthma patients, their close relatives and a comparison group from five cities in France for more than 20 years.
The current study is based on 971 adults for whom complete dietary, weight (BMI), asthma symptom score and demographic data were obtained up until 2011 to 2013.
Dietary intake was measured using food frequency questionnaires encompassing 118 items in 46 food groups. Cured meat intake - ham, sausage, salami - was classified as low for one or fewer weekly servings, medium for one to four weekly servings and high for four or more.
Asthma symptoms such as difficulty breathing, chest tightness and shortness of breath in the preceding 12 months were scored from zero to five (asthma symptom score).
Information was also gathered on other potentially influential factors, such as smoking, regular physical activity, age, sex and educational attainment.
From 2003 to 2007, 42% of the participants said they had asthma at some point, and around half (51%) had never smoked. Just over a third (35%) were overweight, while almost one in 10 (9%) were obese.
Participants said they ate an average of 2.5 servings of cured or processed meat a week.
By 2011 to 2013, when the next checks were made, there had been no change in asthma symptom score for just over half the participants (513). In one in five (20%), symptoms had worsened and in around one in four (27%), symptoms had improved.
Among those who ate one or fewer weekly servings, the proportion of those with worsening asthma symptoms was 14%. Among those eating one to four the proportion was 20% and among those eating four or more, the proportion was 22%.
After taking account of potentially influential factors such as smoking, regular physical activity, age, sex and educational attainment, those who ate the most cured meats were 76% more likely to experience worsening asthma symptoms than those who ate the least.
Being overweight or obese, which has previously been linked to worsening asthma, accounted for 14% of this association, the calculations showed, suggesting that processed meat intake may have an independent role in asthma symptoms, according to the researchers.
This was an observational study, so no firm conclusions can be drawn about cause and effect and the survey responses relied on memory.
The researchers said the symptom score may have been affected by smoking or COPD - chronic lung disease that shares many of its symptoms with asthma.