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Background: With increasing prevalence of overweight and obesity, it is important to study how body mass index (BMI) change may affect lung function among subjects with asthma. There are few prospective studies on this topic, especially with separate analyses of those with normal and high BMI. The aim of the present study was to prospectively study the association between annual BMI change and annual lung function decline, separately among those with normal initial BMI and overweight/obesity, in an adult asthma cohort.

Methods: A population-based adult asthma cohort was examined at study entry between 1986 and 2001 and at follow-up between 2012 and 2014 (n=945). Annual BMI change was analysed in association with annual decline in forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC) and FEV1 /FVC separately in those with normal weight (BMI 18.5–24.9) and overweight/obese subjects (BMI ⩾25) at study entry. Regression models were used to adjust for sex, age, smoking, inhaled corticosteroids use and occupational exposure to gas, dust or fumes.

Results: Overweight/obese subjects had lower FEV1 and FVC but slower annual FEV1 and FVC decline compared to those with normal weight. After adjustment through regression modelling, the association between BMI change with FEV1 and FVC decline remained significant for both BMI groups, but with stronger associations among the overweight/obese (FEV1 B[Overweight/obese] =−25 mL versus B[normal weight] = −15 mL). However, when including only those with BMI increase during follow-up, the associations remained significant among those with overweight/obesity, but not in the normal-weight group. No associations were seen for FEV1 /FVC.

Conclusions: BMI increase is associated with faster FEV1 and FVC decline among overweight and obese adults with asthma in comparison with their normal-weight counterparts.

Background: Asthma is a common disease and a major public health concern. Respiratory symptoms are related to its prognosis, which in turn associates with lung function. Still this association on a long-term basis is not entirely understood.

Aim: To study the association of the type and number of respiratory symptoms with FEV 1 and FEV 1 decline in women and men with asthma.

Method: A population-based cohort of adults with asthma was examined at study entry between 1986 and 2001 and at follow-up between 2012 and 2014, and n=977 had valid measurements of FEV 1 on both occasions. Data regarding respiratory symptoms at study entry (recurrent wheeze, dyspnoea, longstanding cough and productive cough) were analysed in relation to FEV 1 and annual decline in FEV 1, both unadjusted and adjusted for other potentially associated factors by linear regression.

Results: For both sexes recurrent wheeze and dyspnoea were associated with lower FEV 1 at study entry and follow-up, while productive cough was associated with lower FEV 1 only at follow-up. No associations were found between the type of symptoms and annual decline in FEV 1. In adjusted analyses, the association between recurrent wheeze and lower FEV 1 both at study entry and follow-up remained significant among women. Also, the association between a higher number of symptoms with lower FEV 1 both at study entry and follow-up were present for both sexes and remained after adjustment.

Conclusions: Particularly recurrent wheeze and a higher number of respiratory symptoms may predict lower lung function also in the long run among women and men with asthma.