Hypertension and respiratory health in biomasssmoke-exposed premenopausal Indian women

Anindita Dutta & Manas Ranjan Ray

Received: 11 June 2013 /Accepted: 29 November 2013# Springer Science+Business Media Dordrecht 2013

Abstract We aimed to examine how chronic biomass smokeexposure affects prevalence of different respiratory symptoms,chronic obstructive pulmonary disease (COPD), and lungfunction decrement; and how these changes in pulmonaryhealth are related to pollutant levels inside the kitchen. Wealso investigated if these changes are associated with presenceof hypertension. Two hundred and forty-four women usingbiomass fuel (median age 34 year) and 236 age-matchedcontrol women who cooked with liquefied petroleum gas(LPG) were enrolled for this purpose. Questionnaire surveywas used for respiratory symptom prevalence, spirometry forlung function assessment, and laser photometer for particulatematter <10 and 2.5 μm in diameter (PM10 and PM2.5, respec-tively) in cooking areas. Biomass users had higher prevalenceof upper and lower (p <0.05) respiratory symptoms, poorerlung function (64.3 vs. 26.3 % in control, p <0.05), and higherprevalence of COPD (6.6 vs. 1.7 % in control, p <0.05) andhypertension (29.5 vs. 11.0 % in control, p <0.05). Significantpositive association between exposure variables and respira-tory symptoms, lung function measurements, COPD preva-lence, and hypertension were noticed, after adjusting for po-tential confounders. The findings suggest involvement ofbiomass smoke in deterioration of health status of thebiomass-using rural women.

Keywords Biomasssmoke . Indoorairpollution .Respiratorysymptoms . Lung function . COPD . Hypertension

Introduction

About 80 % of rural households in India still depend onunprocessed solid biomass such as wood, animal dung, andagricultural refuse for cooking and room heating. Biomassusers are usually poor people who cannot afford cleaner fuellike electricity or liquefied petroleum gas (LPG). Biomassemits high level of smoke during burning. Moreover, cookingis usually done in traditional stoves that are not vented outside.As a result, smoke remains in cooking areas for prolongedperiod leading to high level of indoor air pollution (IAP). In atypical Indian household, the concentration of particulate pol-lutant during cooking with biomass reaches levels severaltimes higher than the air quality standard recommended bythe US Environmental Protection Agency (Balakrishnan et al.2002). Another important point is that a large number of poorfamilies in the villages do not possess separate kitchen. Theyusually do the cooking in a space adjacent to living room.

Biomass smoke is essentially not different from cigarettesmoke and it contains a large number of health-damagingchemicals including high level of particulate matter of differ-ent sizes, carbonmonoxide, oxides of nitrogen, formaldehyde,acrolein, benzene, toluene, styrene, 1,3-butadiene, and poly-cyclic organic hydrocarbons including benzo(a )pyrene andtransitional metals like Cu, Fe, Ni, Al, and Zn (Morawskaand Zhang 2002). Volatile organic compound like benzeneand polycyclic aromatic hydrocarbon such as benzo(a )pyreneare mutagenic and carcinogenic. It is reasonable to assumetherefore that chronic exposures to these pollutants may causecellular alterations in exposed cells particularly those at thedirect line of exposure such as cells of the nasopharynx, oralcavity, airways, and the lung.

A. Dutta (*)The Energy and Resources Institute, India Habitat Centre, LodhiRoad, New Delhi 110003, Indiae-mail: anidu14@gmail.com

A. DuttaCollege of Environmental Sciences and Engineering, PekingUniversity, Beijing 100871, China

A. Dutta :M. R. RayDepartment of Experimental Hematology, Chittaranjan NationalCancer Institute, 37, S.P. Mukherjee Road, Kolkata 700 026, India

Air Qual Atmos HealthDOI 10.1007/s11869-013-0228-5

There have been a number of investigations on the impactof air pollution exposures on the respiratory system in theWestern world (Zemp et al. 1999). In comparison, little isknown about the pulmonary response in India excepting thatwhich associated biomass smoke with lung function decre-ment and interstitial lung disease (Behera 1997). The respira-tory physiology of the Indians and their socioeconomic statusare different from that of Western population. Since thesevariables are known to influence lung activity (Harik-Khanet al. 2001; Jacobs et al. 1992; Korotzer et al. 2000; Myers1984; Rossiter and Weill 1974; Schoenberg et al. 1978),results obtained from Western studies may not be relevant tothe Indian situation. Hence, epidemiological studies are re-quired among Indian population to examine the effect of airpollution on the pulmonary health status. Accordingly, thisstudy was undertaken with four main aims: (1) to examinehow the women exposed to IAP from biomass burning dif-fered from the LPG users in the prevalence of different respi-ratory symptoms, (2) to measure lung function decrementamong the participants, (3) to relate changes in pulmonaryhealth with particulate pollutant level inside the kitchen, and(4) to examine if there is any association of lung functionparameters with hypertension. Also, since chronic obstructivepulmonary disease (COPD) plays an important role in pro-gression of CVD (Rutten et al. 2006), the prevalence of COPDamong hypertensive patients has been investigated. Hyperten-sion has been given importance in this study as we havepreviously shown that hypertension is very much prevalentamong the biomass users (Dutta et al. 2011). Also, hyperten-sion has been shown to be related to impaired lung function(Margretardottir et al. 2009).

Methods

Participant recruitment, sample size, and study period

A total number of 480 apparently healthy, nonsmoking pre-menopausal married women with regular menstrual cycle (28±2 days) from 10 villages in Hooghly, Burdwan, and Howrahdistricts ofWest Bengal, a state in eastern India, were recruitedfor this population-based cross-sectional study. Villages hadbeen selected on the basis of probability framing and some-times, based on prior information from nongovernment orga-nizations and personal sources. The villages were (1) locatedat least 5 km away from the national or state highways, (2) hadno air-polluting industry such as thermal power plant, brickkiln, sponge iron factory, and rice mill within 5 km radius, (3)had no arsenic contamination in groundwater, a serious publichealth problem in this part of the country, and (4) both LPGand biomass are used for domestic cooking by the villagers.We selected the households in a particular village if they weresolely dependent on LPG or biomass as cooking fuel and were

not mixed fuel (LPG plus biomass) users. Cluster samplingmethod had been chosen to reduce unwanted costs. Thesample size was determined by the formula (Machin et al.1997): t2×p (1−p )/m2 where t was confidence level at 95 %(=1.96), p was estimated prevalence of hypertension in thestudy area that was 10 % (=0.1) based on available data(Gupta 1997), and m was margin of error at 5 % (=0.05).Though precision analysis was used for sample size determi-nation, the number of samples is based on the number ofsubjects that were available in those villages who matchedour study criteria at that point of time.

We carried out the study during 2009–2011 in the summer,autumn, and winter months.We avoided monsoon because (1)most of the remote villages in the state become inaccessible tomotor vehicles during long rainy season from middle of Juneto September and (2) relative humidity during monsoon oftenrises above 95 % when laser photometers cannot functionproperly (Ramachandran et al. 2003).

Among the participants, 244 women aged between 22 and41 years (median 34 year) used to cook exclusively with solid,unprocessed biomass fuel such as dried cow dung cake, wood,dried leaves, jute stick, hay, and paddy husk. They weregrouped as biomass users. The remaining 236 women, aged23–40 year (median 33 year) cooked with cleaner fuel LPG.Accordingly, they were grouped as reference or control. Anaverage of 24 biomass- and LPG-using women was recruitedfrom each village and they were examined simultaneously inmedical camps organized in the villages.

Inclusion and exclusion criteria

The inclusion criteria were apparently healthy, premenopaus-al, married, nonsmoking, tobacco non-chewing women whocook regularly with either biomass or LPG for the past 5 yearsor more. Exclusion criteria were mixed fuel users, pregnant, orlactating women or those currently under medication andwomen with family history of CVD. Included participantsdid not report any previous history of having tuberculosis.

Measurement of PM10 and PM2.5 in indoor air

Particulate matter with aerodynamic diameter <10 μm (PM10)and 2.5 μm (PM2.5) were measured in the cooking areas withreal-time laser photometer (Dust-Trak™ Aerosol Monitor,model 8520; TSI Inc., Shoreview, MN, USA) that contained10-mm nylon Dor-Oliver cyclone and operated at a flow rateof 1.7 l/min, measuring particle load in the concentrationrange of 1 μg to 100 mg/m3. The monitor was calibrated tothe standard ISO 12103-1 A1 test dust. We used two monitorsfor simultaneous measurement of PM10 and PM2.5. Air sam-pling was carried out in each household for three consecutivedays, 8 h/day (0700–1500 hours) covering cooking and non-cooking time. The mean of 3 days was used as the indoor air

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quality of a single household. As biomass-using women cookin a sitting position 2–3 ft away from the open chullah (oven),the monitor was placed in the breathing zone of the cook 2.5 ftabove the floor level on a wooden stool 3 ft away from thechullah. LPG users, on the other hand, cook in a standingposition and the monitor was placed accordingly at a height of4.5 ft. Exposure measurements were carried out simultaneous-ly during the period when we measured the health outcomes.

Extent of exposure

Lifetime exposure to cooking smoke was expressed as hour-years (cooking hours per day×years of cooking×365) follow-ing the procedure of Ozbay et al (2001). Lifetime exposurewas classified into three categories on the basis of hour-years:category 1, ≤10,000; category 2, 10,000–20,000; and category3, >20,000 hour-years.

Questionnaire survey

Information regarding age, education, personal habits, occu-pation of the participants, cooking hours per day, cookingyears, kitchen and fuel type, family, occupation of the spouse,environmental tobacco smoke (ETS), and average familyincome was obtained through personal interview using struc-tured questionnaire (Liard and Neukirch 2000). Each questionwas clearly explained to the participants in Bengali (mothertongue) so that they could figure them out and reply suitably.Socioeconomic status (SES) was ascertained following theprocedure of Tiwari et al (2005). Prevalence of the respiratorysymptoms experienced in the past 3 months was ascertainedfrom questionnaire survey using structured questionnairebased on the respiratory questionnaire of British MedicalResearch Council (BMRC; Cotes 1987), American ThoracicSociety (ATS) and National Heart and Lung Institute Divisionof Lung Diseases (DLD) questionnaire (ATS-DLD-78C;Ferris 1978), and Compendium of Respiratory StandardQuestionnaires (CORSQ).

The symptoms were broadly grouped into two: upper re-spiratory symptoms (URS) and lower respiratory symptoms(LRS; Pope and Dockery 1999). URS included sinusitis (in-flammation of the lining of the sinuses, which are hollow areasof the skull of the bones around the nose), rhinitis (runny orstuffy nose), sore throat, and common cold and fever. LRSincluded dry cough, cough with phlegm, wheeze, chest dis-comfort, difficulty in breathing, or breathlessness. Dyspneawas assessed following the modified, six-point Medical Re-search Council (MRC) dyspnea scale that consists of sixquestions about perceived breathlessness (Eltayara et al.1996). In addition, the prevalence of physician-diagnosedasthma was recorded. The Institutional Ethics Committee ofChittaranjan National Cancer Institute, Kolkata, approved thestudy. Prior informed consent was taken from the participants.

Pulmonary function test

Pulmonary function test (PFT) by spirometry was per-formed with informed consent of the participant, usingelectronic, battery-operated spirometer (Schiller SpirovitSP-1, Baar, Switzerland). The spirometer was calibratedat 2-h intervals with 2-l calibrator syringe accurate to±1 % in ambient conditions and volume for body tem-perature, pressure, and saturation (BTPS) correction.PFT was performed on individuals in a sitting positionwith nose closed by nose clips following the protocol ofAmerican Thoracic Society (1995). The subjects wereasked to take the deepest breath they can, and thenexhale into the sensor as hard as they can, as long aspossible, preferably for 6 s or longer. Each subjectperformed three maximal efforts after detailed instruc-tion and the highest one was recorded. The age, stand-ing height with shoes removed, and body weight ofeach participant were recorded prior to PFT. Body mass index(BMI) was calculated from weight and height of each subjectand expressed in kilograms per square meter.

Forced vital capacity (FVC), i.e., the volume of air (inliters) that could be maximally forcefully exhaled; forcedexpiratory volume in 1 s (FEV1), i.e., the volume of air (inliters) that was forcefully exhaled in 1 s; the ratio of FEV1 toFVC (FEV1/FVC), expressed as percentage; mid-expiratoryflow (FEF25–75%), which is the average expiration flow rateduring the middle 50% of FVC; and peak expiratory flow rate(PEFR), which is the peak flow rate during expiration wererecorded. Miller’s prediction quadrant (1956) was used toclassify the type of lung function deficits into three categories:(1) Restrictive type: FVC<80% of predicted value and FEV1/FVC>70 % of predicted; (2) Obstructive type: FVC>80 % of predicted and FEV1/FVC<70 % of predicted;(3) Combined type: FVC<80 % of predicted and FEV1/FVC<70 % of predicted.

Diagnosis of COPD

COPD was initially diagnosed on the basis of symptoms ofchronic bronchitis, i.e., presence of cough and expectorationson most of the days for at least 3 months in a year for twoconsecutive years or more. Confirmation of diagnosis andfurther classification of COPD (stage I, mild; stage IIa, mod-erate; stage IIb, severe; and stage III, very severe) were doneon the basis of spirometric values following the criteria ofGlobal Initiative for Chronic Obstructive Lung Diseases(GOLD; Pauwels et al. 2001).

Diagnosis of hypertension

Systolic and diastolic blood pressures (SBP and DBP, respec-tively) were measured while the participants were at rest in a

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sitting position by digital sphygmomanometer (Omron, In-dia). Guidelines of the British Hypertension Society werefollowed for blood pressure measurement (O’Brien et al.1997). Hypertension was diagnosed following the SeventhReport of the Joint Committee on the Prevention, Detection,Evaluation, and Treatment of High Blood Pressure (JNC-72003) and the 2003 recommendation of the World HealthOrganization/International Society of Hypertension(Whitworth 2003). The hypertensive condition was confirmedwhen SBP rose to 140 mmHg or more, or DBP elevated to90 mmHg or more. For each participant, we made three bloodpressure measurements with an interval of 24 h.

Statistical analysis

The results were statistically analyzed using StatisticalPackage for Social Sciences statistical software (SPSSfor windows, release 10.0, SPSS Inc., Chicago, IL,USA). Statistical differences were determined by usingChi-square test, Student’s t test, and Mann–Whitney Utest, as applicable. We used multivariable unconditionallogistic regression methods to calculate odds ratio (OR)and 95 % confidence intervals (CIs) to assess associa-tions between exposure to biomass smoke and preva-lence of attributes. Multiple regression analysis wasused to construct the required models incorporatingcombinations of the different measured variables. Themodel balancing the highest correlation coefficient andgreatest statistical significance was selected and reportedin this study. Any measured parameter was treated as avar iab le , e i ther con t inuous (when comput ingunivariately) or dichotomous (when examining associa-tion). Statistical significance was assigned at p <0.05.

Results

Demographic characteristics of the participants

Demographic characteristics of biomass- and LPG-using wom-en are compared in Table 1. It is apparent that the two groupswere well matched except for education, family income, andpresence of separate kitchen (Table 2). Compared with womenin the control group, biomass users were less educated, hadlower family income, and 40.6 % of their households lackedseparate kitchen against 10.6 % of control (Table 1).

Particulate pollution in indoor air

The 8-h mean concentration of PM10 in cooking areas ofbiomass-using households was 276±108 (s.d.) μg/m3 in con-trast to 97±36 μg/m3 in LPG-using households (p <0.001).Like PM10, the mean PM2.5 concentration was significantly

higher in biomass-using households (156±63 vs. 52±27 μg/m3 in LPG-using households; p <0.001). The ranges andmedian values of PM10 and PM2.5 concentrations in biomassand LPG-using households are shown in Fig. 1. The 25th and75th percentile levels of PM10 in biomass-using homes were168.0 and 384.0 μg/m3, respectively, against 61.0 and132.0 μg/m3 in LPG-using households. The 25th and 75thpercentile levels of PM2.5 were 93.0 and 218.0 μg/m

3, respec-tively, in biomass-using households against 26.0 and 78.0 μg/m3 in LPG-using homes.

Even in non-cooking hours, PM10 and PM2.5 levels inbiomass-using households were about 1.8-times higher thanthat of LPG-using households (108.4 vs. 56.1 μg/m3,p <0.001 for PM10; 57.8 vs. 32.4 μg/m

3, p <0.001 for PM2.5).

Prevalence of respiratory symptoms

Both upper and lower respiratory symptoms were moreprevalent among IAP-exposed women compared withthe control group (p < 0.05 in Chi-square test;Fig. 2a, b). Significantly higher prevalence of respirato-ry symptoms among the IAP-exposed group suggestsgreater risk of underlying respiratory infections amongthe exposed subjects.

Recurrent rhinitis (runny or stuffy nose), frequentsore throat, and common cold with fever were the mostprevalent URS among IAP-exposed women. Likewise,cough with phlegm (sputum-producing cough), breath-lessness on exertion, and chest discomfort were themajor LRS encountered. Most prevalent LRS amongbiomass users was breathlessness on exertion (Fig. 2b).The finding was corroborated by dyspnea prevalencedata (Fig. 2c). Complaints of dyspnea (MRC score >0)were made by more than half (57.0 %) of biomass-using women in contrast to one-fifth (19.1 %) of age-matched LPG-using women (p <0.001). Besides higherprevalence, the degree of dyspnea was more severe inbiomass users (Fig. 2c). Doctor-diagnosed asthma wasprevalent in 9.8 % biomass users compared to 2.5 %LPG users.

Biomass-using women exposed to smoke for more than10,000 hour-years (category 2 and 3) exhibited higher preva-lence of respiratory symptoms, both URS and LRS, comparedto category 1 (≤10,000 hour-years). Nearly 63% of those withany type of respiratory symptoms belonged to categories 2and 3.

Reduction in pulmonary function

Compared with the reference group, the biomass users hadpoorer lung function. Overall, lung function was reduced in157 (64.3 %) women cooking with biomass fuel in contrast to62 (26.3 %) of reference group (Table 3). Restrictive type of

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lung deficit was the most predominant (31.6 % for biomassusers vs. 15.7 % for control women; p <0.05 in Chi-square

test). Combined type of lung function deficits was the secondmost common type of lung impairment. In addition to higherprevalence, biomass users had higher instances of severereduction in lung function (Table 3).

The spirometric measurements are presented in Table 4.The mean FVC was 800 ml less than the control (34.8 % lessthan the control) among rural women who were chronicallyexposed to IAP due to cooking with biomass fuels for the past5 years or more. The mean FEV1 was reduced by 600 ml(28.6 %) among biomass users, while the FEF25–75% (mid-expiratory flow rate) was reduced by 21.7 % and PEFR by32.1 % (Table 4).

FEF25–75% declined below 80 % of predicted value in47.5 % of biomass users. In the control group, 19.9 %of the participants had FEF25–75% value less than 80 %predicted, suggesting obstruction in the small airways.Therefore, spirometric measurements indicate 2.4-timesgreater prevalence of small airway obstruction amongrural women exposed to biomass smoke compared withage-matched control group. The magnitude of this re-duction was further categorized as mild (60–79 % ofpredicted value), moderate (40–59 % of predicted val-ue), and severe (below 40 % of predicted value). Mildreduction was noticed in 19.3 % of biomass users (vs.11.4 % in control; p =0.019), moderate in 16.8 % (vs.4.7 % in control; p =0.000), and severe in 11.5 %biomass users (vs. 3.8 % in control; p =0.000).

Decline in PEFR below 80% of predicted value was foundin 53.7 % of biomass users compared to 21.2 % of LPG users.Mild reduction (60–79 % of predicted value) was noticed in

Table 1 Sociodemographiccharacteristics of the participants

LPG liquefied petroleum gas

p <0.05 compared with control in*Chi-square test, **Mann–Whit-neyU test, and ***Student’s t test

Parameter LPG user (n =236) Biomass user (n=244) P value

Age in year, median (range) 33 (23–40) 34 (22–41) >0.05

20–29 year (%) 38.6 36.9 0.784

30–39 year (%) 58.5 59.4 0.906

≥40 year (%) 2.9 3.7 0.639

Body mass index (kg/m2), median (range) 23.7 (22.6–24.8) 23.4 (22.2–24.1) >0.05

Years of cooking, median (range) 15 (5–18) 16 (5–20) >0.05

5–14 year (%) 54.7 53.3 0.850

≥15 year (%) 45.3 46.7 0.835

Cooking hours per day, median (range) 3.0 (3–5) 3.5 (3–6) >0.05

Homes with separate kitchen (%) 89.4 59.4* 0.002

Smokers in the family (%) 51.3 53.7 0.738

Years of schooling, median (range) 9 (0–15) 4 (0–10)** <0.05

Food habit, mixed (%) 98.3 98.8 0.960

Occupation of the participants

Household works only (%) 88.6 86.9 0.857

Household+agricultural work (%) 11.4 13.1 0.615

Alcohol drinking habit (%) 0 0 1.000

Members in family, median (range) 4 (3–6) 5 (3–8) >0.05

Average family income per month (in US $) 85 43*** <0.001

Table 2 Potential riskfactors and confoundersfor measured parameters,unadjusted ORs, and95 % CIs

OR odds ratio; CI confi-dence intervala Reference group

Characteristics OR (95 % CI)

Age (years)

20–29a 1.00

30–39 1.10 (1.04–1.25)

≥40 1.48 (1.14–2.42)

Years of cooking

5–14 1.00

≥15 0.99 (0.86–1.19)

Kitchen location

Separatea 1.00

Adjacent 1.32 (1.06–1.72)

Years of schooling

0–5 1.24 (1.02–1.68)

6–10 1.01 (0.94–1.56)

11–15a 1.00

Food habit

Vegetarian 0.31 (0.12–0.64)

Nonvegetariana 1.00

Environmental tobacco smoke exposure

Noa 1.00

Yes 0.81 (0.46–1.00)

Average monthly family income (US $)

≤40 1.45 (1.08–1.96)

>40a 1.00

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24.2 % of biomass users (vs. 10.2 % in control), moderate(40–59 % of predicted value) in 17.6 % (vs. 8.5 % in control),and severe (below 40 % of predicted value) in 11.9 % ofbiomass users (vs. 2.5 % in control).

Though higher prevalence of reduced lung function wasnoticed among exposure categories 2 and 3 compared tocategory 1, the difference between the two groups (2 and 3)was not significant. Of the 157 biomass-using women whohad impaired lung function, only 18 belonged to category1, while 66 belonged to category 2 and remaining 73were from category 3.

Prevalence of COPD

COPD was diagnosed in 6.6 % biomass-using women against1.7 % of control women (Table 3). The finding is particularly

important because all the participating women were youngand they never smoked in their life. The difference in COPDprevalence between IAP-exposed and control women washighly significant in Chi-square test (p <0.05). Besides theprevalence, the severity of COPD was also greater in IAP-exposed women (Table 3).

Prevalence of hypertension

Seventy-two biomass-using women (29.5 %) of this study hadhypertension and 96 (39.3 %) had prehypertension. In con-trast, 26 (11.0 %) LPG-using women had hypertension and 45(19.1 %) had prehypertension. The difference in the preva-lence of hypertension and prehypertension between these twogroups was highly significant in Chi-square test (p <0.001)Biomass users had higher prevalence of systolic, diastolic, andsystolic plus diastolic hypertension than their age-matchedneighbors who used to cook with LPG (Fig. 3).

Association between the various attributes of the study

1. Exposure variablesExposure variables (PM10, PM2.5) were significantly

associated with measured parameters in multivariate lo-gistic regression analysis even after adjusting for age,exposure years, kitchen location, family income, and ed-ucation (Tables 5 and 6). Several models were constructedwith adjustment made for the above covariates singly or incombination. Results of the model in which adjustmentfor all covariates had been made are presented here(Tables 5 and 6). Associations found in this studywere robust.

2. LRS, FEV1, COPDA lower FEV1 value was found to be associated with

wheeze (OR=3.32; 95 % CI, 1.45–7.63) and breathless-ness (OR=1.99; 95 % CI, 1.17–3.39).

COPD also had significant association with LRS likecough with phlegm (OR=1.14; 95 % CI, 1.10–2.24),breathlessness (OR=1.11; 95 % CI, 1.01–2.03), andwheeze (OR=1.12; 95 % CI, 1.02–2.14).

3. Hypertension, FEV1, COPDSignificant association of lowered FEV1 (OR=1.45;

95 % CI, 1.23–2.26) and COPD (OR=1.42; 95 % CI,1.18–2.29) with hypertension was evitable after makingadjustments for the confounding variables.

Discussion

This study has shown a few important findings related to thehealth of premenopausal women chronically exposed to in-door air pollution from biomass fuel use in the villages.

BiomassLPG

450

360

270

180

90

0

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BiomassLPG

300

200

100

0

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Fig. 1 Concentrations of particulate matter (PM) during cooking hoursinside kitchens using exclusively LPG or biomass fuel for cookingpurpose. a PM10 level, b PM2.5 level. The lines across each box plotrepresent the median value. The lines that extend from the top and thebottom of each box represent the lowest and highest observations stillinside the lower and upper limit of confidence. The difference betweenthese two groups was statistically significant (p <0.05) inMann–WhitneyU test

Air Qual Atmos Health

Compared to their LPG-using neighbors, biomass usersshowed greater prevalence of respiratory symptoms, higherreduction in lung function, and more prevalence of COPD.These findings are imperative because to our knowl-edge, this is first study of its kind in eastern part ofIndia that have actually dealt with observing the respi-ratory health status of poor underprivileged womenwhose health generally go unnoticed.

The women of this study were never smokers and tobacconon-chewers. Also, exposures to ETS were comparable betweenthe groups. Hence, the prevalence of COPD which was found tobe 6.6 % among biomass users compared to only 1.7 % in thecontrol group may only be attributed to the chronic exposurecaused to biomass smoke during cooking. Biomass smokeexposure-related COPD have been reported in other parts ofthe world as well (Amoli 1998; Ozbay et al. 2001; Pandey1984). COPD hasmostly been reported to have developed above40 years of age (Amoli 1998; Ozbay et al. 2001). This is aconspicuous finding of our study as only about 4 % ofbiomass-using women were aged above 40 years. Since alladjustments had been made during data analysis regarding thepotential confounders, we assume that this finding calls forattention as COPD is life threatening. The finding might wellbe due to the reason that village girls in this part of the country getinvolved in doing household chores including cooking from a

very early age, which sometimes is as young as 10 to 12 years.Also, they get married at a very tender age, mostly by 15–18 years. Hence, their exposure to biomass smoke often rangebetween 15 to nearly 25 years by the time they reach 40 years ofage. As a result, COPD is prevalent at such a higher percentageof biomass-usingwomen as it has been hypothesized that womenwho have been cooking with biomass for 15 years are at 2–4times greater risk of developing COPD (Smith et al. 2001).

Similarly, biomass users exhibited greater prevalence ofURS and LRS. Presence of respiratory symptoms generallyindicates underlying respiratory illness or problem in theairways and the alveoli. Therefore, greater prevalence ofURS and LRS in these never-smoking biomass users perhapsindicate higher incidence of respiratory diseases and/or airwayand alveolar damage following cumulative exposure to smokeemitted from burning biomass. This is not unlikely becauseearlier studies have associated pollutant exposure with a hostof respiratory diseases in humans (Albalak et al. 1999; Pandey1984; Routledge et al. 2006; Smith et al. 2000; Sunyer et al.2006). Physician-diagnosed asthma was also more prevalentamong IAP-exposed women of this study.

Significant reduction of lung function was a common find-ing in rural women who used to cook with highly pollutingbiomass fuel. Compared with control, about 64 % of biomass-using rural women had reduced lung function. This finding

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Fig. 2 Prevalence (in percent) ofupper respiratory symptoms (a 1 ,sinusitis; 2 , runny or stuffy nose;3 , sore throat; 4 , common coldand fever), lower respiratorysymptoms (b 1 , dry cough; 2 ,cough with phlegm; 3 , wheezingbreath; 4 , chest discomfort ortightness), and dyspnea (c 0 ,absence of dyspnea; 1–5 ,increasing severity of dyspneaaccording to six-point MedicalResearch Council dyspnea scale)among the rural females cookingwith LPG (control) and biomassfuel (exposed). *p<0.05 in Chi-square test compared withliquefied petroleum gas-usingcontrols

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could be due to the fact that rural girls start cooking from theirchildhood, when the lung is still developing and hence, ismore vulnerable to air toxics. It is known that lung develop-ment becomes complete only at the age of 18–20 years infemales (Tager et al. 1988).

Biomass smoke contains a host of pollutants(Morawska and Zhang 2002) besides containing partic-ulate matter. PMs have only been used as a surrogate,in this study, for all the health-damaging pollutants thatare constituents of the biomass smoke. We did notmeasure pollutants other than PM, which in all likeli-hood may have played a role in mediating health effectsof IAP. Hence, some of the effects observed might be aconsequence of unmeasured co-pollutant exposures. Ad-verse respiratory health has well been associated withwood smoke constituents (Naeher et al. 2007). Giventhe adjustments made during constructing models for

data analysis in this study, the findings may well bedefined to be due to the effects of chronic exposure tobiomass smoke during cooking.

Besides IAP, however, socioeconomic factors can in-fluence lung activity. In fact, social class and poor airquality are independently associated with decreased lungfunction (Wheeler and Ben-Sholmo 2005). Biomassusers in this study were less educated and poorer, andpoverty is generally linked with malnutrition that affectslung development during childhood via respiratory mus-cle weakness and overall energy deficiency (Glew et al.2004). Difference in nutrition between biomass andLPG users, however, was perhaps small because therewas little difference in BMI between these two groups.Moreover, after adjusting for potential confounders, thepositive association between particulate pollution, espe-cially PM2.5, and lung function decrement remained.

Table 4 Comparison of spiro-metric measurements among theparticipants

Results are expressed as mean±SD; adjusted for age, exposureyears, kitchen location, family in-come, and education

CI confidence interval

Variables LPG user (n =236) Biomass user (n =244) 95 % CI

FVC (l) 2.3±0.9 1.5±0.6 0.7 to 0.9

FVC (% Predicted) 86.4±24.7 67.8±23.9 14.3 to 23.0

FEV1 (l) 2.1±0.7 1.5±0.7 0.5 to 0.7

FEV1 (% Predicted) 88.6±30.9 69.8±26.6 13.6 to 24.0

FEV1/FVC (% Predicted) 101.1±22.4 99.2±47.2 −4.7 to 8.5

FEF25–75% (l/s) 2.3±1.2 1.8±0.9 0.3 to 0.7

PEFR (l/s) 2.8±1.3 1.9±1.3 0.7 to 1.1

Table 3 Prevalence (in percent) of reduced lung function and COPD

Variables LPG user (n=236) Biomass user (n=244) ORa (95 % CI)

Normal lung functionb 174 (73.7) 87 (35.7) 1.00

Lung function deficits 62 (26.3) 157 (64.3*) 5.07 (3.43–7.49)

Restrictive 37 (15.7) 77 (31.6*) 4.16 (2.60–6.65)

Obstructive 12 (5.1) 31 (12.7*) 5.17 (2.53–10.56)

Combined 13 (5.5) 49 (20.1*) 7.54 (3.88–14.64)

Magnitude of lung function reduction

Mild 38 (16.1) 81 (33.2*) 4.26 (2.68–6.78)

Moderate 18 (7.6) 43 (17.6*) 4.78 (2.60–8.77)

Severe 6 (2.5) 33 (13.5*) 11.0 (6.47–15.12)

COPD (%)

Stage I 3 (1.3) 8 (3.3*) 5.33 (1.38–9.60)

Stage IIa 1 (0.4) 6 (2.5*) 12.0 (5.42–16.19)

Stage IIb 0 (0) 2 (0.8*) ∞Stage III 0 (0) 0 (0) NaN

Results are expressed as number (%) of individuals; more than one symptom was present in many subjects

URS upper respiratory symptoms, LRS lower respiratory symptoms, COPD chronic obstructive pulmonary disease, OR Odds ratio, CI Confidenceinterval; NaN not a number

*p <0.05 compared with control in Chi-square testa Odds ratio after adjusting for age, exposure years, kitchen location, family income, and educationb Reference

Air Qual Atmos Health

Another important derivation of this study is the associa-tion of hypertension with reduced FEV1 and presence ofCOPD. Prevalence of hypertension has always remained animportant finding in our study (as was also reportedpreviously; Dutta et al. 2011). Our finding of the associationof hypertension with impaired lung function, more preciselylower FEV1, goes in conformation with that ofMargretardottiret al (2009).

A part of this study relied on self-disclosed personal datathat can suffer from bias and some degree of subjectivity. But

since the researchers were constantly present along with theparticipants helping them out with any difficulties they werefacing in understanding the questions or any other issues, wehope to have reduced the bias to some extent. Despite theselimitations, it seems that chronic inhalation of biomass smokeis a major risk factor for developing respiratory symptoms,lung function reduction, and COPD.

To the best of our knowledge, this study is the first of itskind in India to have investigated the association betweenhypertension and poor respiratory health. Since millions ofpoor women of the country are exposed to biomass smokewhile cooking, indoor air pollution poses a great public healthproblem that warrants concerted efforts to design and imple-ment pollution abatement strategies. Also, anatomical differ-ences facilitate greater deposition of inhaled particles inwomen’s lung (Jaques and Kim 2000). In view of this, greaterhealth risk in women than men has been suggested for inhaledparticulate matter (Kim and Hu 1998). It is, therefore, reason-able to assume that the function of this organ could be ad-versely affected following interactions with air toxics, more soin case of women. Hence, efforts should be made by allconcerned to reduce smoke exposure by improving kitchenventilation and by increasing combustion efficiency of theoven. As a long-term measure, however, biomass should bereplaced by cleaner fuel such as LPG or natural gas.

Acknowledgments The study was funded by the Council of Scientificand Industrial Research, India and Central Pollution Control Board underMinistry of Environment and Forests, Government of India.

Conflict of interest The authors declare that they have no potentialconflict of interest.

Table 6 Stratified analyses of association between exposure variables(PM2.5) and respiratory symptoms, lung function measurements, COPDprevalence, and hypertension

Attributes ORa (95 % CI) ORb (95 % CI)

Exposure variable: PM2.5

URS 0.65 (0.42–1.01) 0.73 (0.21–1.45)

LRS 1.23 (1.21–1.97) 1.46 (1.17–2.33)

Lung function impairment 1.61 (1.59–3.63) 1.74 (1.31–4.03)

COPD 2.72 (2.64–4.01) 2.89 (2.15–4.88)

Decline in FVC 1.32 (1.17–1.47) 1.37 (1.10–1.53)

Fall in FEV1 1.37 (1.13–1.48) 1.41 (1.09–1.58)

Reduction in FEF25–75% 1.39 (1.29–1.66) 1.52 (1.12–1.83)

Decline in PEFR 1.42 (1.41–1.57) 1.48 (1.41–1.61)

Hypertension 1.31 (1.28–1.99) 1.41 (1.22–2.08)

OR Odds ratio, CI Confidence interval, URS upper respiratory symp-toms, LRS lower respiratory symptoms, COPD chronic obstructive pul-monary diseasea Unadjusted odds ratiob Odds ratio after adjusting for age, exposure years, kitchen location,family income, and education

Table 5 Stratified analyses of association between exposure variable(PM10) and respiratory symptoms, lung function measurements, COPDprevalence, and hypertension

Attributes ORa (95 % CI) ORb (95 % CI)

Exposure variable: PM10

URS 0.72 (0.31–1.98) 0.88 (0.29–2.01)

LRS 2.96 (1.84–3.01) 1.34 (1.14–1.51)

Lung function impairment 2.64 (2.21–2.71) 1.53 (1.31–3.77)

COPD 1.41 (1.39–1.54) 1.41 (1.22–2.08)

Decline in FVC 1.30 (1.20–1.31) 1.27 (1.07–1.42)

Fall in FEV1 1.33 (1.14–1.35) 1.25 (1.03–1.45)

Reduction in FEF25–75% 1.49 (1.29–1.56) 1.33 (1.09–1.62)

Decline in PEFR 1.06 (0.81–1.29) 1.25 (1.03–1.45)

Hypertension 1.61 (1.29–1.78) 1.35 (1.14–1.95)

OR Odds ratio, CI Confidence interval, URS upper respiratory symp-toms, LRS lower respiratory symptoms, COPD chronic obstructive pul-monary diseasea Unadjusted odds ratiob Odds ratio after adjusting for age, exposure years, kitchen location,family income, and education

69.9

4.20.9

5.911.0

19.1 *16.0

*3.7

9.8

*29.5

*39.3

*31.1

0

40

80

1 2 3 4 5 6

Per

cent

age

of in

divi

dual

sLPG user

Biomass user

Fig. 3 Prevalence (in percent) of hypertension among women cookingwith LPG (control) and biomass fuel (exposed). *p <0.05 in Chi-squaretest compared with liquefied petroleum gas-using controls. 1 , normalblood pressure (SBP<120 and DBP<80 mmHg); 2 , prehypertensive(SBP 120–139 and DBP 80–89 mmHg); 3 , hypertensive (SBP≥140and/or DBP≥90 mmHg); 4 , systolic hypertension (SBP≥140 and DBP<90mmHg); 5 , diastolic hypertension (DBP≥90 and SBP<140 mmHg);6 , systolic+diastolic (SBP≥140 and DBP≥90 mmHg); SBP, systolicblood pressure; DBP, diastolic blood pressures

Air Qual Atmos Health

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