Vulnerability to winter mortality in elderly people in Britain: population based study
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《英国医生杂志》
1 London School of Hygiene and Tropical Medicine, London WC1E 7HT
Correspondence to: P Wilkinson paul.wilkinson@lshtm.ac.uk
Abstract
In the United Kingdom mortality greatly increases in winter.1 This is apparent at all ages but is greatest in relative and absolute terms in elderly people.2 3 Much of the excess seems to be related to cold,4 5 yet Britain has a larger seasonal fluctuation in mortality than many other countries of continental Europe and Scandinavia despite having milder winters.6 Behavioural factors may partly explain this,7 but poor housing may also be important.2 To date there have been few opportunities to examine the personal factors that predispose to increased mortality in winter.
We studied mortality in people aged 75 years, focusing on individual determinants of vulnerability, including socioeconomic factors, sex, home heating, and previous health.
Methods
Month to month variation in mortality (adjusted for region and time trend) accounted for 17% of annual all cause mortality, but only 7.8% after adjustment for the effects of low temperatures (fitted as the mean temperature over the index and previous 13 days) in the daily time series model (fig 2). It accounted for 12.6% when we adjusted for influenza A counts without adjustment for low temperature, and 5.2% when we adjusted for both. Thus, most of the seasonal fluctuation seems to be related to cold, with smaller components attributable to influenza A and other risk factors.
Fig 2 Fraction of deaths attributable to monthly variation, adjusted for region, time trend, and stated covariates
Overall, there were 4221 deaths in 42 162 person years of follow up in winter months (100.1 deaths per 1000 person years, 95% confidence interval 97.1 to 103.1) and 5902 in 77 227 person years of follow up in other months (76.4 deaths per 1000 person years, 74.5 to 78.4).
All analysed variables showed an association with the absolute risk of death in both winter and non-winter months, though there was little difference with factors listed as home circumstances (living alone, reported difficulty making ends meet, and difficulty keeping the house warm) (table 1).
Table 1 Rates of death in winter and non-winter months, ratio of rates, and relative change in winter:non-winter ratios with levels of potential modifying factors
The overall winter:non-winter rate ratio was 1.31 (1.26 to 1.36), which is slightly higher than that found in this age group in the country as a whole.2 There was little evidence that this ratio varied by geographical region or age (table 1). Women, however, had a larger winter:non-winter ratio than men for reasons other than their greater age, previous health status, social isolation, or socioeconomic position (table 2).
Table 2 Rate ratios (95% confidence intervals) for excess winter death, all causes: women relative to men*
There was little evidence of a trend of increasing risk of excess winter death with socioeconomic group, housing tenure (not tabulated), or reported difficulty in making ends meet or in keeping the house warm. Nor was there clear evidence that the combination of low socioeconomic group and reported difficulty in keeping the house warm (a combination expected to identify people least able to heat their home properly) was associated with excess risk (table 3). Those who lived alone seemed no more vulnerable than others.
Table 3 Rate ratios (95% confidence interval) for excess winter death (all causes) in relation to difficulty keeping house warm and Carstairs deprivation group, adjusted for age, sex, and region
Of the various markers of illness and activity status (table 1), only a history of respiratory illness was associated with winter death; the relative risk adjusted for age, sex, and region being 1.20 (1.08 to 1.34). There was no evidence that excess winter death was associated with current smoking, total pack years of cigarettes smoked (not shown), or alcohol consumption. The more detailed assessment of mental health showed no association of the winter ratio with cognitive impairment (mini-mental state examination < 17) or depression (geriatric depression scale 6).
For most variables, the confidence intervals provide evidence against a substantial increase in risk (most exclude increases above 10%). The exceptions include: often having difficulty keeping the house warm (1.14 (0.89 to 1.46), the upper confidence limit for which is compatible with an appreciable increase), frailty, shortness of breath, a history of cardiovascular disease, and consumption of 7 units of alcohol a week.
Pre-existing respiratory disease (asthma, emphysema, or pneumonia diagnosed by a doctor, or a positive response to questions on chronic cough or phlegm) was the single strongest predictor of excess winter death (table 4). It was most clearly associated with death from cardiovascular disease. The ratio of winter:non-winter cardiovascular mortality in those with respiratory disease relative to those without was 1.23 (1.02 to 1.47), and this figure varied only slightly with adjustment for different combinations of potential confounding factors (results not tabulated). History of wheeze or asthma or pneumonia in particular seemed to contribute to this higher relative risk, though history of phlegm for three months a year (a marker of chronic obstructive airways disease) did not. In contrast, there was no evidence that pre-existing respiratory illness increased excess respiratory death, nor that cardiovascular illness increased excess cardiovascular death. The finding that death from non-cardiorespiratory causes was greater in participants with a history of myocardial infarction is noteworthy but may be due to chance.
Table 4 Rate ratios (95% confidence intervals) for excess winter death associated with markers of pre-existing medical illness. All rate ratios adjusted for region, age, sex, and fifth of Carstairs deprivation score
Discussion
Curwen M. Excess winter mortality: a British phenomenon? Health Trends 1990/91;22: 169-75.
Wilkinson P, Landon M, Armstrong B, Stevenson S, McKee M. Cold comfort: the social and environmental determinants of excess winter death in England, 1986-1996. York: Joseph Rowntree Foundation; 2001.
Laake K, Sverre JM. Winter excess mortality: a comparison between Norway and England plus Wales. Age Ageing 1996;25: 343-8.
Pattenden S, Nikiforov B, Armstrong B. Mortality and temperature in Sofia and London. J Epidemiol Community Health 2003;57: 628-33.
Armstrong B, Wilkinson P, Stevenson S. Identifying components of seasonal variation in mortality. Epidemiology 2000;11: S113.
McKee C. Deaths in winter: can Britain learn from Europe? Eur J Epidemiol 1989;5: 178-82.
Eurowinter Group. Cold exposure and winter mortality from ischaemic heart disease, cerebrovascular disease, respiratory disease, and all causes in warm and cold regions of Europe. Lancet 1997;349: 1341-6.
Fletcher A, Jones D, Bulpitt C, Tulloch A. The MRC Trial of assessment and management of older people in the community: objectives, design and interventions. BMC Health Serv Res 2002;2: 21.
Carstairs V, Morris R. Deprivation and health in Scotland. Health Bull Edinb 1991;48: 162-175.
Schwartz J, Spix C, Touloumi G, Bacharova L, Barumamdzadeh T, le Tertre A, et al. Methodological issues in studies of air pollution and daily counts of deaths or hospital admissions. J Epidemiol Community Health 1996;50(suppl 1): S3-11.
Bruzzi P, Green SB, Byar DP, Brinton LA, Schairer C. Estimating the population attributable risk for multiple risk factors using case-control data. Am J Epidemiol 1985;122: 904-14.
Huber P. Robust statistics. New York: John Wiley, 1981.
Sheth T, Nair C, Muller J, Yusuf S. Increased winter mortality from acute myocardial infarction and stroke: the effect of age. J Am Coll Cardiol 1999;33: 1916-9.
Aylin P, Morris S, Wakefield J, Grossinho A, Jarup L, Elliott P. Temperature, housing, deprivation and their relationship to excess winter mortality in Great Britain, 1986-1996. Int J Epidemiol 2001;30: 1100-8.
Carstairs V. Deprivation indices: their interpretation and use in relation to health. J Epidemiol Community Health 1995;49(suppl 2): S3-8.
Lawlor DA, Harvey D, Dews HG. Investigation of the association between excess winter mortality and socio-economic deprivation. J Public Health Med 2000;22: 176-81.
Shah S, Peacock J. Deprivation and excess winter mortality. J Epidemiol Community Health 1999;53: 499-502.
van Rossum CT, Shipley MJ, Hemingway H, Grobbee DE, Mackenbach JP, Marmot MG. Seasonal variation in cause-specific mortality: are there high-risk groups? 25-year follow-up of civil servants from the first Whitehall study. Int J Epidemiol 2001;30: 1109-16.
Keatinge WR, Coleshaw SR, Holmes J. Changes in seasonal mortalities with improvement in home heating in England and Wales from 1964 to 1984. Int J Biometeorol 1989;33: 71-6.
Woodhouse PR, Khaw KT, Plummer M. Seasonal variation of blood pressure and its relationship to ambient temperature in an elderly population. J Hypertens 1993;11: 1267-74.
Stout RW, Crawford VL, McDermott MJ, Rocks MJ, Morris TC. Seasonal changes in haemostatic factors in young and elderly subjects. Age Ageing 1996;25: 256-8.
Bokenes L, Alexandersen TE, Osterud B, Tveita T, Mercer JB. Physiological and haematological responses to cold exposure in the elderly. Int J Circumpolar Health 2000;59: 216-21.
Neild PJ, Syndercombe Court D, Keatinge WR, Donaldson GC, Mattock M, Caunce M. Cold-induced increases in erythrocyte count, plasma cholesterol and plasma fibrinogen of elderly people without a comparable rise in protein C or factor X. Clin Sci (Lond) 1994;86: 43-8.
Smolander J. Effect of cold exposure on older humans. Int J Sports Med 2002;23: 86-92.
Goodwin J, Taylor RS, Pearce VR, Read KL. Seasonal cold, excursional behaviour, clothing protection and physical activity in young and old subjects. Int J Circumpolar Health 2000;59: 195-203.(Paul Wilkinson, senior le)
Correspondence to: P Wilkinson paul.wilkinson@lshtm.ac.uk
Abstract
In the United Kingdom mortality greatly increases in winter.1 This is apparent at all ages but is greatest in relative and absolute terms in elderly people.2 3 Much of the excess seems to be related to cold,4 5 yet Britain has a larger seasonal fluctuation in mortality than many other countries of continental Europe and Scandinavia despite having milder winters.6 Behavioural factors may partly explain this,7 but poor housing may also be important.2 To date there have been few opportunities to examine the personal factors that predispose to increased mortality in winter.
We studied mortality in people aged 75 years, focusing on individual determinants of vulnerability, including socioeconomic factors, sex, home heating, and previous health.
Methods
Month to month variation in mortality (adjusted for region and time trend) accounted for 17% of annual all cause mortality, but only 7.8% after adjustment for the effects of low temperatures (fitted as the mean temperature over the index and previous 13 days) in the daily time series model (fig 2). It accounted for 12.6% when we adjusted for influenza A counts without adjustment for low temperature, and 5.2% when we adjusted for both. Thus, most of the seasonal fluctuation seems to be related to cold, with smaller components attributable to influenza A and other risk factors.
Fig 2 Fraction of deaths attributable to monthly variation, adjusted for region, time trend, and stated covariates
Overall, there were 4221 deaths in 42 162 person years of follow up in winter months (100.1 deaths per 1000 person years, 95% confidence interval 97.1 to 103.1) and 5902 in 77 227 person years of follow up in other months (76.4 deaths per 1000 person years, 74.5 to 78.4).
All analysed variables showed an association with the absolute risk of death in both winter and non-winter months, though there was little difference with factors listed as home circumstances (living alone, reported difficulty making ends meet, and difficulty keeping the house warm) (table 1).
Table 1 Rates of death in winter and non-winter months, ratio of rates, and relative change in winter:non-winter ratios with levels of potential modifying factors
The overall winter:non-winter rate ratio was 1.31 (1.26 to 1.36), which is slightly higher than that found in this age group in the country as a whole.2 There was little evidence that this ratio varied by geographical region or age (table 1). Women, however, had a larger winter:non-winter ratio than men for reasons other than their greater age, previous health status, social isolation, or socioeconomic position (table 2).
Table 2 Rate ratios (95% confidence intervals) for excess winter death, all causes: women relative to men*
There was little evidence of a trend of increasing risk of excess winter death with socioeconomic group, housing tenure (not tabulated), or reported difficulty in making ends meet or in keeping the house warm. Nor was there clear evidence that the combination of low socioeconomic group and reported difficulty in keeping the house warm (a combination expected to identify people least able to heat their home properly) was associated with excess risk (table 3). Those who lived alone seemed no more vulnerable than others.
Table 3 Rate ratios (95% confidence interval) for excess winter death (all causes) in relation to difficulty keeping house warm and Carstairs deprivation group, adjusted for age, sex, and region
Of the various markers of illness and activity status (table 1), only a history of respiratory illness was associated with winter death; the relative risk adjusted for age, sex, and region being 1.20 (1.08 to 1.34). There was no evidence that excess winter death was associated with current smoking, total pack years of cigarettes smoked (not shown), or alcohol consumption. The more detailed assessment of mental health showed no association of the winter ratio with cognitive impairment (mini-mental state examination < 17) or depression (geriatric depression scale 6).
For most variables, the confidence intervals provide evidence against a substantial increase in risk (most exclude increases above 10%). The exceptions include: often having difficulty keeping the house warm (1.14 (0.89 to 1.46), the upper confidence limit for which is compatible with an appreciable increase), frailty, shortness of breath, a history of cardiovascular disease, and consumption of 7 units of alcohol a week.
Pre-existing respiratory disease (asthma, emphysema, or pneumonia diagnosed by a doctor, or a positive response to questions on chronic cough or phlegm) was the single strongest predictor of excess winter death (table 4). It was most clearly associated with death from cardiovascular disease. The ratio of winter:non-winter cardiovascular mortality in those with respiratory disease relative to those without was 1.23 (1.02 to 1.47), and this figure varied only slightly with adjustment for different combinations of potential confounding factors (results not tabulated). History of wheeze or asthma or pneumonia in particular seemed to contribute to this higher relative risk, though history of phlegm for three months a year (a marker of chronic obstructive airways disease) did not. In contrast, there was no evidence that pre-existing respiratory illness increased excess respiratory death, nor that cardiovascular illness increased excess cardiovascular death. The finding that death from non-cardiorespiratory causes was greater in participants with a history of myocardial infarction is noteworthy but may be due to chance.
Table 4 Rate ratios (95% confidence intervals) for excess winter death associated with markers of pre-existing medical illness. All rate ratios adjusted for region, age, sex, and fifth of Carstairs deprivation score
Discussion
Curwen M. Excess winter mortality: a British phenomenon? Health Trends 1990/91;22: 169-75.
Wilkinson P, Landon M, Armstrong B, Stevenson S, McKee M. Cold comfort: the social and environmental determinants of excess winter death in England, 1986-1996. York: Joseph Rowntree Foundation; 2001.
Laake K, Sverre JM. Winter excess mortality: a comparison between Norway and England plus Wales. Age Ageing 1996;25: 343-8.
Pattenden S, Nikiforov B, Armstrong B. Mortality and temperature in Sofia and London. J Epidemiol Community Health 2003;57: 628-33.
Armstrong B, Wilkinson P, Stevenson S. Identifying components of seasonal variation in mortality. Epidemiology 2000;11: S113.
McKee C. Deaths in winter: can Britain learn from Europe? Eur J Epidemiol 1989;5: 178-82.
Eurowinter Group. Cold exposure and winter mortality from ischaemic heart disease, cerebrovascular disease, respiratory disease, and all causes in warm and cold regions of Europe. Lancet 1997;349: 1341-6.
Fletcher A, Jones D, Bulpitt C, Tulloch A. The MRC Trial of assessment and management of older people in the community: objectives, design and interventions. BMC Health Serv Res 2002;2: 21.
Carstairs V, Morris R. Deprivation and health in Scotland. Health Bull Edinb 1991;48: 162-175.
Schwartz J, Spix C, Touloumi G, Bacharova L, Barumamdzadeh T, le Tertre A, et al. Methodological issues in studies of air pollution and daily counts of deaths or hospital admissions. J Epidemiol Community Health 1996;50(suppl 1): S3-11.
Bruzzi P, Green SB, Byar DP, Brinton LA, Schairer C. Estimating the population attributable risk for multiple risk factors using case-control data. Am J Epidemiol 1985;122: 904-14.
Huber P. Robust statistics. New York: John Wiley, 1981.
Sheth T, Nair C, Muller J, Yusuf S. Increased winter mortality from acute myocardial infarction and stroke: the effect of age. J Am Coll Cardiol 1999;33: 1916-9.
Aylin P, Morris S, Wakefield J, Grossinho A, Jarup L, Elliott P. Temperature, housing, deprivation and their relationship to excess winter mortality in Great Britain, 1986-1996. Int J Epidemiol 2001;30: 1100-8.
Carstairs V. Deprivation indices: their interpretation and use in relation to health. J Epidemiol Community Health 1995;49(suppl 2): S3-8.
Lawlor DA, Harvey D, Dews HG. Investigation of the association between excess winter mortality and socio-economic deprivation. J Public Health Med 2000;22: 176-81.
Shah S, Peacock J. Deprivation and excess winter mortality. J Epidemiol Community Health 1999;53: 499-502.
van Rossum CT, Shipley MJ, Hemingway H, Grobbee DE, Mackenbach JP, Marmot MG. Seasonal variation in cause-specific mortality: are there high-risk groups? 25-year follow-up of civil servants from the first Whitehall study. Int J Epidemiol 2001;30: 1109-16.
Keatinge WR, Coleshaw SR, Holmes J. Changes in seasonal mortalities with improvement in home heating in England and Wales from 1964 to 1984. Int J Biometeorol 1989;33: 71-6.
Woodhouse PR, Khaw KT, Plummer M. Seasonal variation of blood pressure and its relationship to ambient temperature in an elderly population. J Hypertens 1993;11: 1267-74.
Stout RW, Crawford VL, McDermott MJ, Rocks MJ, Morris TC. Seasonal changes in haemostatic factors in young and elderly subjects. Age Ageing 1996;25: 256-8.
Bokenes L, Alexandersen TE, Osterud B, Tveita T, Mercer JB. Physiological and haematological responses to cold exposure in the elderly. Int J Circumpolar Health 2000;59: 216-21.
Neild PJ, Syndercombe Court D, Keatinge WR, Donaldson GC, Mattock M, Caunce M. Cold-induced increases in erythrocyte count, plasma cholesterol and plasma fibrinogen of elderly people without a comparable rise in protein C or factor X. Clin Sci (Lond) 1994;86: 43-8.
Smolander J. Effect of cold exposure on older humans. Int J Sports Med 2002;23: 86-92.
Goodwin J, Taylor RS, Pearce VR, Read KL. Seasonal cold, excursional behaviour, clothing protection and physical activity in young and old subjects. Int J Circumpolar Health 2000;59: 195-203.(Paul Wilkinson, senior le)