Table 1

Studies included in the meta-analysis investigating the relation between COPD and biomass fuel exposure

Authors	Location	Study design	Population	Sample size	Definition of exposure	Definition of non-exposure	Phenotypes	OR (95% CI)	Smoking status	PBD FEV₁% mean±SD (case/exposed)
Van Gemert et al30	Uganda Rural	CS	≥30 years	297	Indoor biomass fuel exposure	Non-exposed to biomass fuel	COPD	1.7 (0.53 to 5.51)	B	91.8±20.3 (COPD)*
Örnek et al31	Turkey Urban	CS	≥10 years	351	Biomass for cooking or heating	No biomass use	COPD	0.97 (0.42 to 2.22)	B	N/A
Jaganath et al32	Peru Rural/urban	CS	≥35 years	1487	Biomass fuel for daily cooking	Non-biomass fuel	COPD	2.22 (1.02 to 4.81)	B	N/A
Mukherjee et al33	India Rural	CS	23–43 years	1119	Biomass (dung, wood, dried leaves, jute stick, hay)	LPG	COPD	5.18 (1.81 to 20.3)	N	71.8±6.82 (biomass)
Dutta et al34	India Rural	CS	22–41 years	480	Cooking with biomass	Cooking with LPG	COPD	4.07 (1.34 to 12.36)	N	69.8±26.6 (biomass)
Alim et al35	Bangladesh Rural/urban	CS	≥15 years	420	Biomass	Gas	CB	4.62 (1.32 to 16.2)	N	N/A
Sukhsohale et al36	India Rural	CS	≥15 years	760	Biomass	LPG	CB	1.40 (0.82 to 2.41)	N	N/A
Laniado-Laborin et al37	Mexico Urban	CS	≥40 years	1380	Exposure to biomass smoke	Not exposed to biomass smoke	COPD	1.65 (1.24 to 2.2)	B	60.6±21.8 (COPD)
Johnson et al38	India Rural	CS	≥30 years	900	Biomass	Clean fuel (kerosene, LPG)	COPD	1.24 (0.36 to 4.25)	N	N/A
Desalu et al29	Nigeria Rural	CS	≥35 years	269	Biomass fuel	Non-biomass fuel	CB	3.75 (1.07 to 13.16)	N	70.8±9.50 (biomass)
Akhtar et al39	Pakistan Rural	CS	≥10 years	2557	Solid biomass fuels for cooking	LPG for cooking	CB	2.51 (1.65 to 3.83)	N	N/A
Liu et al40	China Rural/urban	CS	≥40 years	1719	Biomass (wood, crop residues)	LPG	COPD	3.11 (1.63 to 5.94)	N	N/A
Xu et al41	China Rural/urban	CC	≥35 years	1396	Firewood/straw	Electricity/gas	COPD	0.98 (0.76 to 1.27)	B	N/A
Orozco-Levi et al12	Spain Urban	CC	>50 years	120	Exposure to wood, charcoal or both smoke	Not exposed to wood, charcoal	COPD	2.24 (0.84 to 6.28)	B	51 (33–75) (COPD)
Regalado et al42	Mexico Rural	CS	≥38 years	845	Using biomass as cooking fuel	Using gas as cooking fuel	COPD	1.5 (0.5 to 4.3)	N	97.8±13.7(biomass)
Sezer et al43	Turkey Rural/urban	CC	≥38 years	148	Biomass use (wood, dung)≥10 years	No exposure to biomass	COPD	1.32 (0.63 to 2.73)	N	N/A
Ekici et al11	Turkey Rural	CS	>40 years	596	Biomass (Wood, grass, crop, dung)	LPG	CB	1.4 (1.2 to 1.7)	N	Exposition index (biomass) 96.2±17.4 (<68.8 hour-years) 95.8±21.5 (68.8–152.4 hour-years) 87.8±26.2 (>152.4 hour-years)
Kiraz et al44	Turkey Rural/urban	CS	≥25 years	344	Biomass for cooking and heating (dung, wood, sticks)	LPG	COPD CB	3.47 (1.19 to 10.11) 2.15 (1.07 to 4.33)	B	Study group (rural/biomass) FEV₁ %: 80.96±12.61 (smokers) FEV₁ %: 82.36±11.48 (non-smokers)
Uzun et al27	Turkey Rural/urban	CS	17–75 years	177	Biomass fuel use (wood)	Non-biomass fuel use	CB	3.36 (1.8 to 6.26)	B	N/A
Golshan et al25	Iran Rural	CS	1 month to 81 years (27.62±16.6)	561	Using wood fuel in the past	Using gas fuel	CB	2.91 (2.08 to 4.4)	B	N/A
Pérez-Padilla et al26	Mexico Urban	CC	>40 years	438	Wood smoke exposure while cooking	No exposure to wood smoke	CB	3.9 (2.0 to 7.6) N 7.2 (2.8 to 20)	B N	N/A
Dennis et al24	Colombia Urban	CC	≥35 years	208	Using wood as cooking fuel	Not using wood as cooking fuel	COPD	3.43 (1.69 to 7.05)	B	FEV₁ % 57.60±13 (COPD)
Dutt et al45	India Urban	CS	15–60 years	195	Biomass	LPG, kerosene	CB	4.17 (0.46 to 38.02)	B	N/A
Behera et al46	India Rural	CS	N/A	3608	Cooking with ‘chulla’ in which biomass fuels are used	Cooking with LPG stove	CB	1.75 (1.03 to 2.98)	N	FEV₁ %: 83.21±1.89 (symptomatic)

*A ll the sample (including men and women) .
B, both smokers and non-smokers; CB: chronic bronchitis; CC, case–control; COPD, chronic obstructive pulmonary disease; CS, cross-sectional; FEV₁, forced expiratory volume for 1 s; LPG, liquefied petroleum gas; N, non-smokers only; N/A, not available; PBD, postbronchodilator.