Asthma symptoms in adults worsened over time with greater consumption of cured meats, only slightly mediated by increases in body mass index, according to a longitudinal study published online December 20 in Thorax.
Cured meats have already been identified as a risk factor for cancer, all-cause mortality, and several chronic diseases, including chronic obstructive pulmonary disease.
"As cured meat is known for its high-nitrite content which may lead to nitrosative stress related airway inflammation — one of the several physiological processes involved in asthma [—] it is reasonable to posit that cured meat intake is an independent risk factor for asthma," write Zhen Li, MD, from the Paul Brousse Hospital in Villejuif, France, and colleagues.
"Since obesity is a likely risk factor for incidence and exacerbations of asthma," and diet affects body mass index (BMI), they note, "it is plausible that BMI lies in the causal pathway between diet and asthma."
The researchers therefore analyzed data from 971 participants, including 42% with asthma, who enrolled in the prospective Epidemiological Study on the Genetics and Environment of Asthma (EGEA) between 2003 and 2007. The researchers included only the adults (average age, 43 years) who completed the food frequency questionnaire and had data on asthma symptoms. Among the 118 items on the food questionnaire, ham (two slices/portion), sausage (one sausage/portion), and dried sausage (two slices/portion) were categorized as cured meats.
Nearly half the participants (48%) had a medium intake, at 1 to 3.9 servings per week, whereas 19% had less than one serving per week and 33% had at least four servings a week. Just more than a third (35%) were overweight and 9% were obese; 51% had never smoked.
During follow-up, conducted from 2011 to 2013, an average 7 years later, 20% of the participants reported having worsening asthma symptoms, defined as greater than 0 on a scale of 0 to 5, based on five symptoms: breathlessness while wheezing, waking up from chest tightness, shortness of breath at rest, shortness of breath after exercise, and waking up from shortness of breath. Most (53%) had no change in their symptoms, and 27% had improved symptoms.
Among those eating at least four servings of cured meats a week, 22% reported worsening asthma symptoms compared with 14% of those who ate less than one serving a week and 20% who ate 1 to 3.9 servings weekly.
The researchers used a marginal structure model, a type of statistical modeling used to infer causality in epidemiology, to estimate the direct effects of cured meat intake on the participants' asthma symptoms. They accounted for other potential dietary confounders using two multifactor dietary patterns: one with a high intake of fruits, vegetables, whole grains, oils, and fish, and one with a high intake of prepared meals, cured meats, condiments, alcohol, sandwiches, French fries, and other potatoes.
The authors also adjusted for age, sex, smoking history, educational level, and physical activity, particularly as sex and smoking history have both previously been associated with cured meat intake. In this study, those who ate more cured meats were also more likely to be men, to be younger, to smoke, to consume more calories, to have a higher BMI, to consume more sodium and saturated fat, and to have asthma.
After these adjustments, participants who ate at least four servings of cured meat per week had 76% greater odds of worsening asthma symptoms than those who consumed less than one serving of cured meat per week (multivariable odds ratio [OR], 1.76; 95% confidence interval [CI], 1.01 - 3.06). When the researchers considered the indirect effects of BMI on asthma symptoms, they determined that BMI accounted for 14% of the total effect of cured meats' influence on asthma symptoms (OR, 1.07; 95% CI, 1.01 - 1.14). However, "[n]o interaction was observed between cured meat intake and BMI...in the associations with asthma" (P = .90).
The indirect effect of high cured meat intake mediated through BMI accounted for only 14% of the association with worsening asthma symptoms, so "the direct effect explained a greater proportion, suggesting a deleterious role of cured meat independent of BMI," the authors conclude. They note, however, that two prospective American studies focused on different cured meats — primarily bacon, hot dogs and sausages — did not find any effect on asthma incidence after adjusting for BMI and other confounders.
"This different finding may result from the role of BMI in the association (confounder vs mediator) or the assessment of respiratory phenotypes (incidence vs change in asthma symptoms)," they write. They also noted a follow-up loss of 15% of participants.
Aside from the possibility of nitrosative and oxidative stress harming the lungs from cured meats' high nitrate levels, the researchers proposed two other mechanisms by which cured meats may worsen asthma. One is an increase in systemic inflammation considering previously identified associations between cured meat intake and C-reactive protein. The other, supported only by sparse evidence with childhood asthma, is that high salt and saturated fat intake may affect asthma symptoms.
The research was funded by Merck Sharp & Dohme, the GA2LEN project, Global Allergy and Asthma European Network, and Conseil scientifique AGIR pour les maladies chroniques, National Hospital program of clinical research. The authors have disclosed no relevant financial relationships.
Thorax. Published online December 20, 2016. Full text
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