The European Journal of Public Health Advance Access originally published online on March 26, 2008
The European Journal of Public Health 2008 18(4):399-405; doi:10.1093/eurpub/ckn015
Miscellaneous |
Home warmth and health status of COPD patients
Liesl M. Osman1, Jon G. Ayres1, Carole Garden1, Karen Reglitz1, Janice Lyon2 and J. Graham Douglas3
1 Department of Environmental & Occupational Medicine, University of Aberdeen, Liberty Safe Work Research Centre, Foresterhill Road, Aberdeen, AB25 2ZP, UK
2 Aberdeen City Council, St Nicholas House, Broad Street, Aberdeen, UK
3 Chest Clinic, Aberdeen Royal Infirmary, Foresterhill, Aberdeen, AB25 2ZN, UK
Correspondence: Liesl M. Osman, NDM-Strategic, Nuffield Department of Medicine, University of Oxford, Richard Doll Building, Roosevelt Drive, Oxford OX3 7LF, tel: 44 1224 558186, fax: 44 1224 551826, e-mail: med078{at}abdn.ac.uk; osman{at}well.ox.ac.uk
Received November 1, 2007, accepted February 11, 2008
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Abstract |
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Background: Home Energy Efficiency guidelines recommend domestic indoor temperatures of 21°C for at least 9 h per day in living areas. Is health status of patients with Chronic Obstructive Pulmonary Disease (COPD) associated with maintaining this level of warmth in their homes? Methods: In a cross-sectional observational study of patients, living in their own homes, living room (LR) and bedroom (BR) temperatures were measured at 30 min intervals over 1 week using electronic dataloggers. Health status was measured with the St George's Respiratory Questionnaire (SGRQ) and EuroQol: EQ VAS. Outdoor temperatures were provided by Met Office. Results: One hundred and forty eight patients consented to temperature monitoring. Patients’ mean age was 69 (SD 8.5) years, 67 (45%) male, mean percentage of predicted Forced Expiratory Volume in one second (FEV1) 41.7 (SD 17.4). Fifty-eight (39%) were current smokers. Independent of age, lung function, smoking and outdoor temperatures, poorer respiratory health status was significantly associated (P = 0.01) with fewer days with 9 h of warmth at 21°C in the LR. A sub analysis showed that patients who smoked experienced more health effects than non-smokers (P < 0.01). Conclusion: Maintaining the warmth guideline of 21°C in living areas for at least 9 h per day was associated with better health status for COPD patients. Patients who were continuing smokers were more vulnerable to reduction in warmth.
Keywords: health status, indoor environment, monitoring elderly, respiratory disease, symptoms and COPD
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Introduction |
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Excess winter morbidity is relatively greater in the United Kingdom than in Scandinavian countries and Germany.1 It has been suggested that lower building standards and thus poorer housing energy efficiency in the United Kingdom2 lead to lower indoor temperatures in winter, which increase vulnerability to illness. In one London borough, Rudge and Gilchrist3 found that census districts with a high Fuel Poverty Risk (associated with low home energy efficiency and defined as the need to spend more than 10% of the household income to maintain recommended indoor temperatures) had significantly higher rates of emergency respiratory admissions in the winters between 1993 and 1997. UK Housing Condition Surveys in the 1990s showed that many homes had indoor temperatures in winter low enough to be uncomfortable and possibly dangerous to health. As a result of concern about these indoor conditions, UK Government policy, expressed through the UK Fuel Poverty Strategy of 2001, has funded affordable warmth programmes such as Warm Front in England and Warm Deal in Scotland. These programmes provide grants to upgrade energy efficiency of homes, so that comfortable warmth can be maintained without risk of fuel poverty.
The WHO recommends4 that living areas in homes should be maintained at a temperature between 18°C and 24°C. UK housing standard guidelines,5 used to establish whether a home has acceptable energy efficiency, recommend that living rooms (LR) should be maintained at 21°C or higher for at least 9 h per day. However, we do not know whether maintenance of these levels of recommended warmth is associated with better health of those in the home.
Perception of the home as cold is related to poor self-reported health and increased respiratory symptoms.6–8 Upgrading insulation and central heating in homes leads to dryer and warmer homes,9,10 and individuals in upgraded homes report better health.11 But improvements in health have not been shown to be directly associated with warmth increase in the homes,10–12 or with maintenance of home indoor temperatures at the level recommended by guidelines.
The studies above suggest a gap remains in evidence for health effects associated with maintenance of the housing temperature guidelines.
The health effects of cold homes are likely to be long-term and insidious, leading to lower resistance to immediate causes of exacerbations such as viral infections. Health status measures such as the St George's Respiratory Questionnaire (SGRQ)13 and Euroqol14 Visual Analogue Scale (VAS) can provide an index of this vulnerability. For people with chronic respiratory disease, poor health status scores predict greater rates of GP contact and higher prospective risk of hospital admission.15,16
Chronic Obstructive Pulmonary Disease (COPD) formerly known as chronic bronchitis, or emphysema, is the fifth largest cause of death worldwide and respiratory exacerbations are a major contributor to incidence of winter illness.17,18 In Scotland, cold weather mortality effects occur from November to May.17 This study asked whether health status of patients with COPD was associated with the number of hours when homes reached recommended standards of indoor warmth in LRs and bedrooms (BR). The study was carried out in the North East of Scotland during autumn, winter and spring 2004–05. Some of the results described in this article have been presented in abstract.19
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Methods |
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This was the initial cross-sectional component of an intervention study. The data presented here are for all participants regardless of their future randomization status. Using NQuery Advisor V5 (Statistical Solutions Stonehill Corporate Center, MA, USA) a sample size of 140 was calculated for 80% power at
= 0.05 to detect a four-point difference in SGRQ means between groups in the main randomized trial. Ethics committee approval for HEARTH study was granted by the Grampian Region Ethical Committee (Ref number 04/S0801/27).
Sample
Patients were admitted to Aberdeen Royal Infirmary with an exacerbation of COPD between January 2003 and October 2004. Patients were classified as eligible if they lived within the Aberdeen City Council boundaries in their own homes. Patients in nursing or sheltered homes, where individual control over heating was not possible, were excluded.
Temperature monitoring
Indoor temperature data were collected from LRs and BRs for 1 week between the end of October 2004 and mid May 2005, using an Escort iLOGTM datalogger, placed 1–1.5 m high (usually on a sideboard in the LR and a bedside table in the BR). They were positioned away from doors and windows and set to take recordings at 30 min intervals. Data were downloaded using Escort iLOGTMsoftware.
Hours of warmth at 21°C for LRs and 18°C for BRs over the monitoring week and average temperature at 5 pm in LRs, were calculated. Daily outdoor temperature data in Aberdeen was provided by the UK Meteorological Bureau.
Self-reported smoking status was verified by salivary cotinine levels. Samples were assayed using Salimetrics high sensitivity salivary cotinine enzyme immunoassay kit. Respondents who reported that they were not current smokers, but had a salivary cotinine level >20 µg l–1 were reclassified as current smokers.20
Patient data
All patients had been reviewed by a hospital physician within the past 2 years, and had a recorded diagnosis of COPD. Lung function measurements [Forced Expiratory Volume in one second (FEV1) and Forced Vitality (FVC)] of subjects at time of review were collected from clinical records.
Social deprivation was assessed by the Carstairs deprivation index.21 This is derived from postcodes and is calculated from four census variables—car ownership, household overcrowding, head of household in social class IV or V and male unemployment. The index is a standardized score with zero as the national mean score and SD of 3.5. A positive score indicates greater disadvantage than average. The Carstairs deprivation index is significantly related to differences in prevalence of chronic health conditions in the United Kingdom.22
A questionnaire was mailed to participants before their first home visit. It included the SGRQ, questions on smoking status of the participant, marital status and postcode (giving deprivation status). At the home visit the questionnaire was collected and checked. Any incomplete or ambiguous responses were clarified with participants.
Health status
The SGRQ is a validated respiratory specific health status measure.13 Scores are generated in three areas: symptoms, activity limitation and disease impact, expressed as percentages ranging from 0 to 100. Higher scores represent worse heath status. A change of four points on an SGRQ scale is regarded as clinically significant.13,23
The EQ VAS14 obtains a self-rating of current health status, using a vertical 20 cm ‘thermometer’. The thermometer has endpoints of 100 (‘best imaginable health state’) and 0 (‘worst imaginable health state’).
Analysis
SPSS 13.0 was used for statistical analyses (SPSS V13, SPSS, Inc., Chicago ILL). Descriptive statistics were collated for temperature monitoring results. Parametric and non-parametric statistics were used as appropriate. Unadjusted associations between demographic, clinical and temperature measures were calculated for SGRQ symptom, activity limitation and disease impact scores and EQ VAS scores. The demographic and clinical variables in analyses included: age, validated smoking status, marital status, Carstairs deprivation score, number of prior admissions for COPD and percentage of predicted FEV1 and FVC (Appendix 1). As FEV1 and FVC were highly correlated (r = 0.61, P < 0.001) only predicted FEV1 was used. Variables with P-values of at least 0.10 in the unadjusted analyses were entered into an ordinary least squared multivariate regression analysis. Using Bonferroni correction for multiple testing of intercorrelated outcomes a P-value of <0.01 was required for significance.
Data were analysed separately for continuing smokers and for non-smokers.
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Results |
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Five hundred and thirty-four patients were invited to take part in an initial housing survey assessing energy efficiency of their homes. Two hundred and fifty-four patients agreed to participate. Of these 46 were not surveyed due to difficulty in contacting to arrange survey, withdrawing from the study, or death. Two patients were found not to have COPD on review of case notes, leaving 206 homes for inclusion. Mean Carstairs deprivation score of those agreeing to be surveyed was close to the national average and did not differ from those not wishing to participate (P = 0.16). After the initial survey 148 (72%) patients agreed to take part in 1-week monitoring of indoor temperature. Patients who agreed to be monitored did not differ in age (68.4 years versus 67.9 years, P = 0.54), gender (55% female in both groups) or deprivation score (0.27 versus –0.16, P = 0.16) from those originally identified and not monitored.
Using GOLD criteria,24 18 patients (12%) were classified as having mild COPD, 91 (61%) had moderate COPD and 39 (26%) had severe COPD. One hundred and eight participants reported that they were not current smokers. Eighteen of these had salivary cotinine levels above 20 µg l–1 (27 µg l–1 –420 µg l–1) and were reclassified as smokers.
Demographic and clinical characteristics of participants are shown in table 1.
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Indoor warmth over 1 week
In the United Kingdom 14°C has been found to be an outdoor threshold associated with increases in respiratory mortality.16 WHO recommended minimum indoor temperature of 18°C.25 In the study homes, median LR temperature at 5 pm was 21°C. Eight participants had 5 pm LR temperatures below 18°C, two had 5 pm temperatures below 14°C.
Although, median indoor temperature appeared acceptable, the housing guideline recommendations for at least 9 h of 21°C warmth per day in LRs were not fulfilled in more than 50% of homes. BRs were more likely to be maintained at recommended levels.
Outdoor temperatures
The average minimum outdoor temperature over the study monitoring weeks was 2.9°C (IQR 1.1–5.0). Average maximum was 10.1°C (IQR 7.1–12.3°C). Table 2 shows that BR, but not LR, warmth had a weak relationship to outdoor temperatures during the monitoring week.
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Hours of warmth: demographic and housing predictors
Social deprivation was not related to hours of warmth in the study week (LR: B = 1.52 SE 1.63, P = 0.35, BR: B = 0.19 SE 1.17, P = 0.91). Age had a weak relationship (B = 1.10, SE 0.63, P = 0.08). Homes without central heating had fewer hours of warmth but the difference was not significant (LR: 64 h versus 61 h P = 0.81, BR: 109 h versus 95 h P = 0.34).
Smoking and health
Smokers were significantly younger than non-smokers (64.9 versus 71.0 years, P < 0.01) and had lower (better) activity limitation scores (80.9 versus 86.5, P = 0.08). They did not differ in symptom (P = 0.54), impact (P = 0.56) or EQ-VAS scores (P = 0.73). Hours of warmth did not differ between smokers and non-smokers homes (LR: P = 0.42; BR: P = 0.48).
Health status and indoor warmth
Tables 3 and 4 shows multivariate models of the relationship of indoor hours of warmth to health adjusted for significant covariates identified in the univariate analyses (Appendix 1).
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SGRQ symptom scores
Symptom scores were significantly related to number of days with 21°C for at least 9 h in LRs. BR days with at least 9 h at 18°C and LR total hours of warmth at 21°C showed a trend to association (P = 0.04) but were not significant at the 0.01 level. The final models explained 13–14% of total variation in symptom scores. The coefficients of –1.10 and –0.93 for days at recommended warmth indicate that a clinically significant reduction of four SGRQ points would be predicted from an increase of 4 days with recommended warmth in LRs and BRs.
When the analyses were stratified by smoking status, the results were in the same direction as in the total model, but were only significant for smokers. The size of the coefficients indicated that the effect of warmth on symptoms was increased for smokers, and reduced for non-smokers. For smokers a four-point improvement in symptom score would be predicted from a 2-day increase in LR days at recommended warmth.
SGRQ activity limitation scores
In the multivariate analysis activity limitation scores were not significantly related to any temperature indices. In the sub-analysis there was a relationship for smokers only, between LR days with warmth of 21°C for 9 h and activity scores. A 5.3 activity score improvement would be predicted from an increase of 2 days warmth.
SGRQ impact scores
Impact scores were lower (better) for patients who had more days with 21°C for 9 h in LRs, but the trend did not reach statistical significance. In the sub-analysis the effect size was 5–10 times greater for smokers, and was significant at the 0.01 level. An almost six-point improvement in impact score would be predicted for a 2-day increase in warmth in LRs of smokers.
EQ VAS
Number of LR days with 21°C for 9 h was associated with better VAS but was not significant at the 0.01 level. There was no association with BR warmth. Effect size was greater for smokers, but not significant.
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Discussion |
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This study found that symptomatic health status of COPD patients is associated with maintaining guideline warmth in their homes during cold months. Patients with fewer days with 21°C for at least 9 h had significantly worse respiratory symptom scores. The associations of illness impact and the EQ VAS with LR and BR warmth were consistent in the same direction, but did not reach significance. Smokers showed more health effect of lesser warmth than non-smokers. Although studies have reported that self-perception of living in a cold house is associated with self-perceived poor health,6–8 and indirect association has been found between colder homes and health,10 no previous study has shown direct relationship between objectively measured indoor hours of warmth and respiratory health status.
The significant relationship between hours of warmth and symptomatic health status was not due to the effects of extremely cold temperatures in the homes studied. Homes were somewhat cooler than is recommended, but most were not very cold. Median LR temperature at 5 pm in the homes studied was 21°C. Only two homes had average 5 pm LR temperatures below 14°C. The results of the study support the belief that there can be health effects of marginally cold homes. This is a finding which needs further exploration, and increased understanding of the possible physiological mechanisms operating to impact on health in these conditions of cool but not severely cold homes.
There was little relationship of indoor to outdoor temperatures. In particular, hours of LR warmth was not associated with outdoor maximum or minimum temperatures. During the study, outdoor temperatures were well below acceptable indoor temperatures, with mean maximum outdoors below 11°C, and mean minimum 3°C. It appears that in very cold periods participants maintain a level of preferred warmth in living areas, which cannot be predicted from outside temperatures. BR hours of warmth did have a significant but weak relationship with outside temperatures. Anecdotally, many of these participants reported a deliberate choice to have lower temperatures in their BRs, and a number kept windows open at night even during winter months. Donaldson et al.26 found similar behaviour patterns (keeping windows open, not heating BRs) among COPD patients in their London study.
This study was not designed to track the effect of changes in outdoor temperature on COPD health, and indoor LR temperatures were independent of outdoor temperatures during the study. Most of our participants were very house bound as can be seen from their high activity limitation scores.
We did not find an association between deprivation score and health status or hours of warmth. Wilkinson et al.18 also found that there was no relationship between socioeconomic status, or reported financial worries and winter death rate among an elderly UK population.
Smokers showed more effects of lower indoor temperatures than non-smokers. As a post hoc analysis these results must be treated with caution, but the associations were large, significant at < = 0.001 and consistent across the respiratory outcome measures. There is evidence that smokers have heightened vascular response to drops in temperature.27,28 Plasma fibrinogen levels and blood coagulation factors are higher in smokers,29 and are also higher in cold months. These factors play a part in the increased risk of stroke and myocardial infarction in winter for smokers.30,31 This suggests that patients with COPD who smoke will have an added health load during winter. On the other hand, fibrinogen has not been found to vary with drops in outdoor temperature.32 The results raise the question of whether indoor temperature and effects of smoking, may mediate or confound the effect of outdoor temperature on fibrinogen production which may impact on symptomatology as much via the cardiovascular as pulmonary route, as patients with COPD have a higher prevalence of ischaemic heart disease.
This study has some limitations. Indoor temperature measurement of hours of warmth was taken over 1 week only, and related to health status measured at the start of that week. Although we know that variation in hours of warmth between homes in the United Kingdom can be large,9 we know little about expected variation within a home over winter months. However, this variability will tend to weaken associations with health status measured at one point in time, and in the present study the association between health status outcomes and hours of warmth was consistent across the SGRQ subscales, and with the generic EQ-VAS measure. The patients taking part in this study were representative in age, sex and deprivation of patients living in the United Kingdom who have had a hospital admission as a consequence of COPD exacerbation, but we do not know if results can be generalized to COPD patients in the UK community who have not had a hospital admission. Behaviour such as sleeping with windows open may also not be generalizable to patients outside the United Kingdom.
Although we have illustrated the dose response impact indicated by the regression coefficients obtained in the model for warmth and health status scores, we must be cautious before making quantitative and causal estimates of this kind in an associational study.
We did not assess outdoor behaviour, which will have contributed to health status. However, if outdoor exposure and behaviour were the main influences on health status then we would not have found significant and consistent relationships with indoor hours of warmth.
The present study is cross-sectional and cannot show whether the poorer health status associated with lower hours of warmth will translate to increased health service use. As part of a larger study, outcomes in the group described in this article will be followed over 2 years. Nonetheless, the present results suggest that a health status burden is associated with fewer indoor hours of warmth.
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Conclusion |
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The results of the study suggest that home indoor warmth influences respiratory health status, and that the 21°C for 9 h index is a useful indicator of whether indoor warmth is sufficient for health. This is a potentially important finding. It supports the emphasis of current UK government policy on funding interventions to achieve affordable warmth for UK homes and hence improve health. Results also support the likelihood of health benefits from liaison programmes between health workers and local Central Heating Programme and Warm Deal workers, where patients’ home living conditions can be professionally assessed, and patients referred to local improvement schemes where need is observed. The study provides information, which could be helpful to patients and their families in reinforcing attempts to stop smoking. Finally, the study raises the question of how we explore possible physiological mechanisms, whereby indoor temperatures and smoking habits, may mediate effects of outdoor temperatures on mortality and morbidity during winter months.
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Acknowledgements |
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We thank the patients who took part in this study and Gordon Kyle, Chief Executive of Castlehill Housing Association, Karen Milne, Project Manager, Aberdeen Care & Repair, Castlehill Housing Association, and Mrs Val Bennett of Aberdeen Care & Repair who carried out the energy surveys. We thank Dr Gordon Prescott, Senior Lecturer in Medical Statistics of the Department of Public Health, University of Aberdeen for statistical advice. The Home Environment And Respiratory HealTH study (HEARTH) is funded by the Eaga Partnership Charitable Trust. Some of the results described in this article have been presented in abstract.
Conflict of interest: None declared.
Key points
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