BMJ  2004;329:647 (18 September), doi:10.1136/bmj.38167.589907.55 (published 17 August 2004)

Paper

Vulnerability to winter mortality in elderly people in Britain: population based study

¹ London School of Hygiene and Tropical Medicine, London WC1E 7HT

Abstract

Objective To examine the determinants of vulnerability to winter mortality in elderly British people.

Design Population based cohort study (119 389 person years of follow up).

Setting 106 general practices from the Medical Research Council trial of assessment and management of older people in Britain.

Participants People aged 75 years.

Main outcome measures Mortality (10 123 deaths) determined by follow up through the Office for National Statistics.

Results Month to month variation accounted for 17% of annual all cause mortality, but only 7.8% after adjustment for temperature. The overall winter:non-winter rate ratio was 1.31 (95% confidence interval 1.26 to 1.36). There was little evidence that this ratio varied by geographical region, age, or any of the personal, socioeconomic, or clinical factors examined, with two exceptions: after adjustment for all major covariates the winter:non-winter ratio in women compared with men was 1.11 (1.00 to 1.23), and those with a self reported history of respiratory illness had a winter:non-winter ratio of 1.20 (1.08 to 1.34) times that of people without a history of respiratory illness. There was no evidence that socioeconomic deprivation or self reported financial worries were predictive of winter death.

Conclusion Except for female sex and pre-existing respiratory illness, there was little evidence for vulnerability to winter death associated with factors thought to lead to vulnerability. The lack of socioeconomic gradient suggests that policies aimed at relief of fuel poverty may need to be supplemented by additional measures to tackle the burden of excess winter deaths in elderly people.

Introduction

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

The study was based on the Medical Research Council trial of the assessment and management of older people in the community,⁸ which involved 106 practices selected from the MRC general practice research framework as representative of the British population. All patients aged 75 years on practice lists were invited to participate unless they were in a long stay hospital or nursing home or were terminally ill. Participants, recruited in 1995-8, underwent a brief multidimensional assessment.

The brief assessment included questions on physical symptoms, number of medications, feelings of depression, activities of daily living, perceived health, and physical activity. Patients were asked about their current alcohol intake, smoking, sociodemographic factors (including marital status, living circumstances, financial difficulties), and home heating ("In the last year have you had difficulty keeping your home warm?"). To provide socioeconomic data for the full sample, we used the home postcode to assign a Carstairs deprivation score to each individual.⁹

We followed up mortality (to 30 March 2001) through the Office for National Statistics. We obtained figures for daily minimum, maximum, and mean temperature from one meteorological station per region from the British Atmospheric Data Centre.

Statistical methods
We used Poisson time series models to assess overall effects of season (month of years as categorical variable), temperature, and influenza (see also bmj.com). To analyse excess mortality in the winter season, we defined winter as December to March. For the main results, the Poisson models included age (four groups), sex, and region and interactions of these with winter. Thus, we tabulated the winter:non-winter ratio for each level (group) of each explanatory variable, and then the ratio of these winter:non-winter ratios relative to that of the baseline group. The latter can be thought of as "relative risks" of excess winter death.

Results

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 in the daily time series model (figure). 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.

View larger version (20K): [in this window] [in a new window]   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).

The table shows the rates of death, ratio of rates, and relative changes in ratios according to 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 (see bmj.com) or age. 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. The rate ratio for all cause excess winter death in women compared with men was (1.11, 1.00 to 1.23).

View this table: [in this window] [in a new window]   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

 

There was little evidence of a trend of increasing risk of excess winter death with socioeconomic group, housing tenure, 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 (see bmj.com). Those who lived alone seemed no more vulnerable than others.

Of the various markers of illness and activity status (table), 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.

For most variables, the confidence intervals provide evidence against a substantial increase in risk (most exclude increases above 10%). 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 (see bmj.com).

Discussion

The results confirm a substantial (around 30%) increase in mortality in winter in people of 75 years, but, remarkably, they point to few of the analysed factors being markers of vulnerability except preexisting respiratory disease and female sex. The higher risk in women is not fully explained but does not seem to be due to clinical or socioeconomic differences.

The role of socioeconomic status
Some of the factors that were unrelated to excess winter death merit comment, especially as many of them were associated with overall mortality, so poor validity is unlikely to explain the lack of association. Perhaps most surprising is socioeconomic status, which showed no gradient in risk, despite the fact that the Carstairs score was a predictor of death rates overall (table), as would be expected from other published studies.¹⁰ Scrutiny of the literature, however, shows that the lack of socioeconomic gradient with winter death has been a consistent finding of UK studies.^{2 11 12-14} If there is a gradient in risk, it is small.

This is a conclusion that policy makers may find unexpected and at odds with current notions of vulnerability from fuel poverty. The explanation may be complex. Firstly, although lower socioeconomic groups have high mortality in absolute terms, it is not obvious that they should also have a high relative increase in deaths during winter months unless they are more exposed to the principal causes of it—specifically low ambient temperature. But we have previously shown that people in lower socioeconomic groups do not on average have cooler homes than people in higher socioeconomic groups.² This may reflect behavioural influences, but also the fact that housing association and local authority dwellings are often as well, or better, heated than owner occupied dwellings,² reflecting the relatively recent construction of much social housing and efforts by local authorities to improve home energy efficiency. Poverty is associated with poorer home heating when heating costs are high, so the lack of increased risk among those reporting difficulty in making ends meet and difficulty in keeping the home warm is surprising, although the results are compatible with an appreciable increase in risk in relation to the latter variable. It could be argued that reported difficulty in keeping the home warm is not a good indicator of low indoor temperatures (though in fact we have found it predictive in a previous study),² and that reported difficulty in making ends meet might not be sensitive for poverty. However, Keatinge and colleagues place more emphasis on personal behaviours and have argued that much excess winter mortality is related to exposure to cold from "brief excursions outdoors rather than to low indoor temperatures."^{7 15} The observed lack of socioeconomic gradient suggests that the risk of excess winter death is quite widely distributed in elderly people, which therefore may limit the potential health impacts of initiatives that are targeted only at low income households. Of course, the situation may be different in other age groups, but it is relevant to recall the relative flatness of excess winter mortality with socioeconomic status in other UK studies not specific to this age group.

The role of pre-existing illness
The fact that frailty and pre-existing cardiovascular illness were unrelated to excess winter death was also surprising as most winter deaths are from cardiorespiratory causes. Paradoxically, respiratory disease seemed to be a strong determinant of cardiovascular but not respiratory death. The specificity of association may have been obscured by misclassification of cause of death, but analyses (not shown) of deaths with any mention of respiratory causes also did not show an association with pre-existing respiratory illness.

Conclusion
The lack of socioeconomic gradient in particular has implications for public heath policies aimed at reducing the burden of winter death, as fuel poverty relief alone may be only partially successful. The fact that the risk of excess winter death seems to be widely distributed in elderly people suggests that additional measures are needed to reach all those at risk.

What is already known on this topic Britain has a large burden of excess winter deaths, much of which is attributable to the effects of cold Around 1.4 to 2 million households in England are in fuel poverty—that is, they would have to spend more than 10% of their income to heat the home to an adequate temperature What this study adds Socioeconomic factors are not strongly associated with winter death in elderly people Female sex and a history of respiratory illness may confer vulnerability The risk of winter death seems to be widely distributed in elderly people rather than being heavily concentrated in the most disadvantaged groups Public heath policies to reduce the burden of winter death in Britain will need to be broad based and to consider measures additional to those aimed at tackling fuel poverty

---

Editorial by Jefferson and articles pp 660, 663

This is the abridged version of an article that was posted on bmj.com on 17 August 2004: http://bmj.com/cgi/doi/10.1136/bmj.38167.589907.55

We thank Chris Bulpitt, Dee Jones, and Alistair Tulloch, coinvestigators on the MRC trial of assessment and management of older people; the nurses, general practitioners, the other staff, and the patients in the participating practices; the MRC general practice research framework coordinating centre, particularly Madge Vickers, Jeannett Martin, and Nicky Fasey; the research team for the MRC trial of assessment and management of older people in the community—Elizabeth Breeze, Edmond Ng, Gill Price, Susan Stirling, Rakhi Kabiwala, and Janbibi Mazar at London School of Hygiene and Tropical Medicine, and Maria Nunes and Ruth Peters at Imperial College; Amina Latif and Elaine Stringer, University of Wales College of Medicine; and the trial steering committee, J Grimley Evans (chair), Andy Haines, Carol Brayne, Karen Luker, and Madge Vickers.

Contributors: See bmj.com

Funding: UK Medical Research Council grants G9900506 and G9223939; and Departments of Health and the Scottish Office. PW was supported by a Public Health Career Scientist Award (NHS Executive, CCB/BS/PHCS031), and PM by project funding from the Wellcome Trust (No 051637).

Competing interests: None declared.

Ethical approval: The relevant local research ethics committees approved the study.

References

1. Curwen M. Excess winter mortality: a British phenomenon? Health Trends 1990/91;22: 169-75.
2. 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.
3. Laake K, Sverre JM. Winter excess mortality: a comparison between Norway and England plus Wales. Age Ageing 1996;25: 343-8.[Abstract/Free Full Text]
4. Pattenden S, Nikiforov B, Armstrong B. Mortality and temperature in Sofia and London. J Epidemiol Community Health 2003;57: 628-33.[Abstract/Free Full Text]
5. Armstrong B, Wilkinson P, Stevenson S. Identifying components of seasonal variation in mortality. Epidemiology 2000;11: S113.
6. McKee C. Deaths in winter: can Britain learn from Europe? Eur J Epidemiol 1989;5: 178-82.[CrossRef][Web of Science][Medline]
7. 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.[CrossRef][Web of Science][Medline]
8. 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.[CrossRef][Medline]
9. Carstairs V, Morris R. Deprivation and health in Scotland. Health Bull Edinb 1991;48: 162-75.
10. Carstairs V. Deprivation indices: their interpretation and use in relation to health. J Epidemiol Community Health 1995;49(suppl 2): S3-8.
11. 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.[Abstract/Free Full Text]
12. 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.[Abstract/Free Full Text]
13. Shah S, Peacock J. Deprivation and excess winter mortality. J Epidemiol Community Health 1999;53: 499-502.[Abstract]
14. 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.[Abstract/Free Full Text]
15. 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.[CrossRef][Web of Science][Medline]

(Accepted 3 June 2004)

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    StumbleUpon    Technorati    What's this?

Relevant Articles

Winter mortality in elderly people in Britain: Action on outdoor cold stress is needed to reduce winter mortality

William R Keatinge and Gavin C Donaldson
BMJ 2004 329: 976. [Extract] [Full Text] [PDF]

Winter mortality in elderly people in Britain: Outdoor exposure and effect of windchill should be taken into consideration

Alan A Woodall
BMJ 2004 329: 976. [Extract] [Full Text]

Winter mortality in elderly people in Britain: Lack of social gradient in winter excess mortality is obvious in Denmark

Roland Rau
BMJ 2004 329: 976-977. [Extract] [Full Text]

Socioeconomic condition does not affect mortality during winter
BMJ 2004 329: 0. [Full Text] [PDF]

How to deal with influenza?

Tom Jefferson
BMJ 2004 329: 633-634. [Extract] [Full Text] [PDF]

Implications of the incidence of influenza-like illness in nursing homes for influenza chemoprophylaxis: descriptive study

Richard Harling, Andrew Hayward, and John M Watson
BMJ 2004 329: 663-664. [Extract] [Full Text] [PDF]

This article has been cited by other articles:

• Falagas, M. E., Karageorgopoulos, D. E., Moraitis, L. I., Vouloumanou, E. K., Roussos, N., Peppas, G., Rafailidis, P. I. (2009). Seasonality of mortality: the September phenomenon in Mediterranean countries. CMAJ 181: 484-486 [Abstract] [Full text]  
• Olson, A. L., Swigris, J. J., Raghu, G., Brown, K. K. (2009). Seasonal Variation: Mortality From Pulmonary Fibrosis Is Greatest in the Winter. Chest 136: 16-22 [Abstract] [Full text]  
• Analitis, A., Katsouyanni, K., Biggeri, A., Baccini, M., Forsberg, B., Bisanti, L., Kirchmayer, U., Ballester, F., Cadum, E., Goodman, P. G., Hojs, A., Sunyer, J., Tiittanen, P., Michelozzi, P. (2008). Effects of Cold Weather on Mortality: Results From 15 European Cities Within the PHEWE Project. Am J Epidemiol 168: 1397-1408 [Abstract] [Full text]  
• El Ansari, W., El-Silimy, S. (2008). Are fuel poverty reduction schemes associated with decreased excess winter mortality in elders? A case study from London, UK. Chronic Illness 4: 289-294 [Abstract]  
• McMichael, A. J, Wilkinson, P., Kovats, R S., Pattenden, S., Hajat, S., Armstrong, B., Vajanapoom, N., Niciu, E. M, Mahomed, H., Kingkeow, C., Kosnik, M., O'Neill, M. S, Romieu, I., Ramirez-Aguilar, M., Barreto, M. L, Gouveia, N., Nikiforov, B. (2008). International study of temperature, heat and urban mortality: the 'ISOTHURM' project. Int J Epidemiol 37: 1121-1131 [Abstract] [Full text]  
• Osman, L. M., Ayres, J. G., Garden, C., Reglitz, K., Lyon, J., Douglas, J. G. (2008). Home warmth and health status of COPD patients. Eur J Public Health 18: 399-405 [Abstract] [Full text]  
• Morris, J., Wilkinson, P., Dangour, A. D, Deeming, C., Fletcher, A. (2007). Defining a minimum income for healthy living (MIHL): older age, England. Int J Epidemiol 36: 1300-1307 [Abstract] [Full text]  
• Hajat, S, Kovats, R S, Lachowycz, K (2007). Heat-related and cold-related deaths in England and Wales: who is at risk?. Occup. Environ. Med. 64: 93-100 [Abstract] [Full text]  
• Gerber, Y., Jacobsen, S. J., Killian, J. M., Weston, S. A., Roger, V. L. (2006). Seasonality and Daily Weather Conditions in Relation to Myocardial Infarction and Sudden Cardiac Death in Olmsted County, Minnesota, 1979 to 2002. J Am Coll Cardiol 48: 287-292 [Abstract] [Full text]  
• Burge, P. S. (2006). Prevention of Exacerbations: How Are We Doing and Can We Do Better?. Proc Am Thorac Soc 3: 257-261 [Abstract] [Full text]  
• Dushoff, J., Plotkin, J. B., Viboud, C., Earn, D. J. D., Simonsen, L. (2006). Mortality due to Influenza in the United States--An Annualized Regression Approach Using Multiple-Cause Mortality Data. Am J Epidemiol 163: 181-187 [Abstract] [Full text]  
• Rudge, J., Gilchrist, R. (2005). Excess winter morbidity among older people at risk of cold homes: a population-based study in a London borough. J Public Health (Oxf) 27: 353-358 [Abstract] [Full text]  
• Barnett, A. G, Dobson, A. J, McElduff, P., Salomaa, V., Kuulasmaa, K., Sans, S., for the WHO MONICA project, (2005). Cold periods and coronary events: an analysis of populations worldwide. J. Epidemiol. Community Health 59: 551-557 [Abstract] [Full text]  
• Rohde, G (2004). The real impact of influenza?. Thorax 59: 1073-1073 [Full text]  
• Keatinge, W. R, Donaldson, G. C (2004). Winter mortality in elderly people in Britain: Action on outdoor cold stress is needed to reduce winter mortality. BMJ 329: 976-976 [Full text]  
• Woodall, A. A (2004). Winter mortality in elderly people in Britain: Outdoor exposure and effect of windchill should be taken into consideration. BMJ 329: 976-976 [Full text]  
• Rau, R. (2004). Winter mortality in elderly people in Britain: Lack of social gradient in winter excess mortality is obvious in Denmark. BMJ 329: 976-977 [Full text]  
• Jefferson, T. (2004). How to deal with influenza?. BMJ 329: 633-634 [Full text]  

Rapid Responses:

Read all Rapid Responses

Common Cold is the Killer, Coagulation and Calcification his Camouflage Net.

Friedrich Flachsbart
bmj.com, 18 Aug 2004 [Full text]

Higher incidence of hip fracture and mortality in winter

Humayon Pervez
bmj.com, 17 Sep 2004 [Full text]

Increased mortality in winter: uncoupling or hypobaric hypoxia?

Richard G Fiddian-Green
bmj.com, 19 Sep 2004 [Full text]

Action on outdoor cold stress is needed to reduce winter mortality

William R Keatinge, et al.
bmj.com, 21 Sep 2004 [Full text]

Lack of Social Gradient in Winter Excess Mortality in Denmark

Roland Rau
bmj.com, 21 Sep 2004 [Full text]

Outdoor exposure and effect of windchill

Alan A Woodall
bmj.com, 22 Sep 2004 [Full text]

The elderly must dress appropriately for winter weather

Jane E K Orr
bmj.com, 22 Sep 2004 [Full text]

Do Europeans worry why their summer mortality is higher than Britains?

Robert G Bunney
bmj.com, 23 Sep 2004 [Full text]

Study conundrum

Stephen J Watkins, et al.
bmj.com, 7 Oct 2004 [Full text]

Online poll

Find out more >>