Diet and obesity exhibit complex interrelationships with asthma, particularly among elderly women. We aimed to clarify the impact of healthy diet assessed by the Alternate Healthy Eating Index-2010 (AHEI-2010) on: 1) the incidence of asthma symptoms, and 2) among women with symptoms in 2011, the change in asthma symptoms, while accounting for the potential mediating role of BMI.

A nested case-control study on asthma with follow-up data.

Within the French E3N cohort.

8,621 elderly women (62 years on average in 1993)

Dietary data were collected in 1993 and 2005 using semi-quantitative questionnaires. Using the validated asthma symptom score assessed in 2011 and 2018, asthma symptom incidence among women with no asthma symptom in 2011 (n=5,700) and change in asthma symptoms (reduced, stable, increased) among those with asthma symptoms in 2011 (n=2,921) were defined. BMI was calculated in 2008. Marginal structural models were used to estimate total, direct and indirect effects mediated by BMI.

After adjustment for potential confounders, we found a significant indirect effect of healthier diet on lower risk of asthma symptoms incidence mediated by lower BMI (OR for AHEI-2010 quintile 5 vs quintile 1=0.95 (0.92-0.97)), without significant total (OR=0.87 (0.66-1.10)) nor direct (OR=0.92 (0.71-1.15)) effects. Among women with asthma symptoms, we also found a significant indirect effect of healthier diet on reduced asthma symptoms mediated by lower BMI (OR for AHEI-2010 >median vs ≤median=1.02 (1.00-1.03)) without significant total (OR=1.12 (0.94-1.34)) nor direct effects (OR=1.10 (0.93-1.31)).

A healthy diet was associated with reduced risk of asthma symptoms over time, partly through a lower BMI.