Background and objective: The role of indoor air pollution as a risk factor for asthma and respiratory symptoms in middle age is unclear. We investigated associations between indoor air pollution sources and (i) asthma phenotypes and (ii) asthma-related respiratory symptoms in middle-aged adults.

Methods: Subjects (n = 5729) who participated in the 2004 survey of the Tasmanian Longitudinal Health Study completed respiratory and home environment questionnaires. Associations between indoor air pollution sources, and asthma phenotypes and asthma-related respiratory symptoms were estimated.

Results: Recent mould in the home was associated with current asthma (odds ratio (OR) 1.26; 95% confidence interval 1.06–1.50), wheeze (OR 1.34; 1.17–1.54) and nocturnal chest tightness (OR 1.30; 1.12–1.51). Stratified by atopy and gender, recent mould was associated with current non-atopic asthma only in males (OR 3.73; 1.29–10.80). More rooms affected by mould were associated with significant trends for current asthma, wheeze and nocturnal chest tightness. Home environmental tobacco smoke was associated with doctor-diagnosed asthma (OR 1.25; 1.02–1.53), wheeze (OR 1.69; 1.41–2.03), nocturnal chest tightness (OR 1.54; 1.26–1.88), with current asthma only in non-smokers (OR 2.09; 95%: 1.30–3.35) and with current asthma only in males (OR 1.74; 95%: 1.25–2.42). Among heating appliances, reverse cycle air conditioning was negatively associated with doctor-diagnosed asthma (OR 0.84; 0.70–1.00). Neither electric nor gas stove use was associated with either asthma phenotype or with asthma-related respiratory symptoms.

Conclusions: In middle age, reducing home exposure to mould and environmental tobacco smoke might reduce asthma and asthma-related respiratory symptoms.