The effects of environmental stressors on the mortality of the oldest old male population in Hong Kong, 1977–2006

Abstract

Although age–sex-specific mortality rates were decreasing over the years, such a trend was not observed for the male population aged 85 or above (the oldest old) in Hong Kong. Despite literature suggesting that environmental stressors were associated with higher mortality, the adverse effects of socioeconomic and political events were seldom included. Hence, this study explored the relationship between environmental stressors covering adverse weather conditions as well as key socioeconomic and political events and fluctuations in the oldest old mortality rates in Hong Kong during the period 1977 to 2006. The oldest old mortality rates in Hong Kong were observed to have a likelihood of being associated with these environmental stressors. Furthermore, men appeared to be more susceptible to these risk factors than did women. More care and attention should be given to the oldest old men, in particular, during periods of socioeconomic or political upheavals. A cohort study would be useful to study these stressors in greater detail.

Keywords:

• Elderly
• environment
• Hong Kong
• mortality
• socioeconomic factors
• weather

Introduction

In general, women enjoy longer life expectancy than do men. In Hong Kong (one of the places in the world with longest life expectancy), the life expectancy of men increased from 70.1 years in 1977 to 79.4 years in 2006; whereas that of women increased from 76.7 years to 85.5 years [1-3]. The increasing life expectancy could be explained by the improved living conditions, better control of infectious diseases and medical advancements, which contributed to the reduction of pre-mature deaths [4]. However, the decrease in mortality is limited by the basic physiology of ageing [5]. Hence, the decreasing trend in mortality might not be always observed. In Hong Kong, the decreasing trend of age-specific mortality rate was not observed for the male population aged 85 or above (the oldest old).

Variation in mortality pattern may be accounted for by pre-existing medical conditions or chronic illnesses [6-9], or other stressors including personal and environmental factors. Psychosocial factors may be a possible mechanism for the adverse effects of stressful events on mortality. External stressors such as socioeconomic conditions probably lead to an increased perception of loss of control, and thus affect the mortality pattern [10]. Furthermore, people with a weak sense of coherence showed slower adaptation to the adverse effect of stressful experiences, and this in turn was associated with excess mortality [11]. Another possible mechanism was in terms of physiological and medical conditions. It was found that the elderly with greater financial stress experienced more nutritional stress due to poorer appetite [12], whereas malnutrition was shown to be associated with an increased mortality [13].

Some environmental stressors may aggravate medical conditions and contribute to higher mortality. This was especially true for the elderly with limited adaptive responses. For example, the occurrence of cerebral infarcts in elderly patients was associated with high temperatures [14]. Various studies showed that people with pre-existing diseases, such as ischemic heart disease, stroke or respiratory illnesses, were more likely to have heat-related deaths [15]. A U-shaped relation between temperature and mortality from coronary artery disease and cerebral infarction, mediated by increased thrombotic tendency from increased blood viscosity [16], has also been documented [17]. Furthermore, the need for increased blood flow to the skin associated with increased sweating can overload already failing hearts and lead to heat-related deaths [18]. For cold-related mortality, this was likely associated with indirect effects involving an increased incidence of influenza and other respiratory infections [19].

There is extensive literature on the relationship between mortality and adverse weather conditions [15],[16],[19-25], or personal stressors [12],[26],[27]. However, even after Goodman et al. pointed out that sociopolitical processes were largely missing from traditional studies [10], to date, there still seems to be a lack of studies on the adverse effects of socioeconomic and political events on mortality, except for some sparse studies on specific events. For example, during the first Iraqi missile attack on Israel, it was found that people with pre-existing cardiac disease were more vulnerable to the effects of extreme emotional stress [28], and excess mortality might be partly caused by acute emotional stress [29]. In Hong Kong, some researchers found that a major epidemic like the outbreak of the Severe Acute Respiratory Syndrome (SARS) was associated with an elevated elderly suicide rate [30],[31].

Life-event checklists facilitate the study of stressful life events. Most studies usually include only personal events such as marriage, death of close relatives or retirement issues, such as the Hong Kong study on depression [32]. However, other studies have shown that environmental stressors operating at the society level were also important. For example, a study in Taiwan found that political issues formed one of the three most frequent stressors identified by the elderly [33].

We hypothesise that fluctuations in the oldest old mortality rate, particularly in the case of men, were likely to be affected by environmental stressors, comprising of socioeconomic, political and climatic factors. This article attempts to highlight the possible association between the mortality rate and the environmental stressors, with an emphasis on socioeconomic and political events.

Methods

In Hong Kong, deaths from natural causes attended by registered medical practitioner were registered at the Births and Deaths Registry. The causes of death were certified by the medical practitioner who attended the deceased. Deaths from unnatural causes were reported to the coroner, who would decide whether investigation and/or inquest were needed. The causes of death were then determined by the coroner and registered at the Births and Deaths Registry. The classification of cause of death was based on the International Statistical Classification of Diseases, Injuries and Causes of Death (ICD-9: 1979–2000; ICD-10: 2001 onwards). For both natural and unnatural deaths, the Births and Deaths Registry would pass the death data to the Census and Statistics Department, which was responsible to compile death statistics, with the validation process assisted by Department of Health.

The annual numbers of deaths from all causes and the size of the population aged 65 or above from 1977 to 2006 were obtained from the Census and Statistics Department. The age–sex-specific mortality rate per 1000 population was calculated based on population estimates.

Decreasing trends in the age–sex-specific mortality rate were examined by fitting linear trend line (y = a + bx) and exponential trend line (y = exp(a + bx)). Hypothesis testing on the regression coefficient, b, was conducted. Decreasing trends were suggested by regression coefficients being statistically significantly (p < 0.05) less than zero. Analyses were performed by SPSS version 14.0.

Year-on-year changes of the oldest old mortality rate were calculated. One-tailed hypothesis testing on two Poisson means were used to identify statistically significant (p < 0.05) year-on-year changes. p-values were calculated by StatCalc 2.0.

Qualitative analysis was used to explore the relation between environmental stressors and fluctuations in the oldest old mortality curve. Key socioeconomic and political events were defined, for technical convenience in this article, as those events which were influential enough to cause possible fluctuations in the Hang Seng Index. The Hang Seng Index is considered one of the instant indicators of economic well-being and political stability in Hong Kong. Information on key events was obtained from the website of the Hang Seng Index Services Limited (www.hsi.com.hk) [34] and the Hong Kong Yearbook (www.yearbook.gov.hk). Information on weather-related stress in Hong Kong was extracted from the analytic paper published by the Hong Kong Observatory [35].

Results

Figure 1 shows the age–sex-specific mortality rate of the population aged 65 or above in Hong Kong from 1977 to 2006. Statistically significant decreasing trends were found in all the age–sex-specific mortality rates (p < 0.001 for both models), except for the male oldest old (p = 0.07 for linear model and p = 0.09 for exponential model). The results in hypothesis testing of decreasing trend were robust to the model assumption as both linear model and exponential model gave the same results.

Figure 1. Age-specific mortality rate in Hong Kong, by sex, 1977–2006.

During the period 1977 to 2006, there were 69,101 deaths and 149,027 deaths among the male and female oldest old populations, respectively. The mortality rate of the male oldest old ranged from 111 per 1000 persons to 163 per 1000 persons, whereas that of the female oldest old ranged from 97 per 1000 persons to 140 per 1000 persons.

As with the other age groups, the oldest old mortality rates of males were higher than those of females over the years. The fluctuation in the mortality curve of the male oldest old was much larger than that of the female. Table I shows the year-on-year percentage changes in the mortality rates of the male and female oldest old. Statistically significant (p < 0.05) year-on-year increase in oldest old mortality rate was observed in years 1978, 1982, 1996, 1998, 2003 and 2004 of the male series, whereas in years 1983, 1986, 1990, 1992, 1996 and 2003 of the female series. Similarly, statistically significant (p < 0.05) year-on-year decrease was observed in years 1981, 1983, 1993, 1995, 2001 and 2006 of the male series, whereas in years 1981, 1984, 1993, 1994, 1995, 2001 and 2006 of the female series. Among these changes, double-digit year-on-year percentage increase in oldest old mortality rate was observed in years 1978, 1982, 1996 and 1998 of the male series, whereas only in years 1996 and 2003 of the female series. Similarly, double-digit year-on-year percentage decrease was observed in years 1981, 1983 and 2001 of the male series, whereas only in years 1984 and 2006 of the female series. It should be noted that, because the reporting of deaths in 2006 might not be complete at the time of analysis, the decrease in mortality rate in 2006 could have been a result of reporting delay. Hence, the drop in 2006 was not conclusive.

Table I.  Year-on-year percentage change in the mortality rates of the male and female oldest old.

Year	Male (%)	Female (%)
1977	–	–
1978	13*	−2
1979	−5	−3
1980	5	−2
1981	−25*	−7*
1982	20*	−2
1983	−12*	7*
1984	−5	−18*
1985	6	−1
1986	3	5*
1987	−1	−2
1988	−1	1
1989	−2	−2
1990	2	8*
1991	−5	−1
1992	3	7*
1993	−9*	−7*
1994	1	−9*
1995	−6*	−6*
1996	12*	13*
1997	3	1
1998	13*	0
1999	2	1
2000	−1	0
2001	−13*	−9*
2002	1	0
2003	5*	11*
2004	5*	1
2005	−2	1
2006	−7*	−15*

*Statistically significant (p < 0.05) year-on-year increase/decrease.

Twenty-one key socioeconomic and political events were identified in the period studied. Table II shows the list of key socioeconomic and political events chosen for the study as well as stressful weather in Hong Kong. Figure 2 shows the oldest old mortality rate curves of males and females in relation to key socioeconomic and political events.

Figure 2. Oldest old mortality rate and key economic and political events in Hong Kong, 1977–2006.

Table II.  Key economic and political events as well as stressful weather in Hong Kong, 1977–2006.

Year	Event/stressful weather	Descriptions	Classification
1977	Stressful summer	Very large net effective temperature index was observed in summer in HK	Atmospheric
1978–1980	Second oil crisis	The political turmoil in Iran reduced oil production and drove oil price up for more than twice	Economic
1982	Property market downturn	Property values in HK have fallen an average of 30% in 6 months	Economic
	Stressful winter	Very small net effective temperature index was observed in winter in HK	Atmospheric
1983	Hong Kong Dollar linked to US Dollar	In response to the abnormal fluctuation in exchange rate (US$1 = HK$9.6), the HK Government established the linked exchange rate for US$1 at HK$7.8	Economic
	Stressful summer	Very large net effective temperature index was observed in summer in HK	Atmospheric
	Stressful winter	Very small net effective temperature index was observed in winter in HK	Atmospheric
1984	Sino-British Joint Declaration on the future of Hong Kong signed	The Declaration confirmed that the sovereignty of HK would be handed over to China from 1 July 1997	Political
	Stressful winter	Very small net effective temperature index was observed in winter in HK	Atmospheric
1986	Hang Seng Index (HSI) Futures contracts launched	As the first exchange-traded financial derivative in HK, the HSI futures contract attracted great interest; within 18 months, it accounted for 93% of the market's turnover	Economic
	Unification of 4 stock exchanges	The 4 stock exchanges were unified as a new exchange, which marked the new era of stock market	Economic
1987	Global stock market crash	HSI in HK dropped over 10% on a single day and the stock market was halt for 4 days; the final drop of HSI was 45.8%	Economic
1989	June 4th incident (also known as the Tiananmen Incident)	The incident was triggered by the conflict between the university students and the Chinese Government and ending up with violence; it weakened the confidence of the people in HK and sparked a massive wave of migration in HK	Political
1994	Sino-British airport financing deal signed	The HK Government decided to build a new airport. As most of the financing would extend beyond the date of sovereignty handover, China was concerned about excessive debt incurred; finally, the British and the Chinese government agreed on the amount of debt arising from the project and this agreement was considered as a significant victory for China	Political
1997	Establishment of the Government of the Hong Kong Special Administrative Region (HKSAR)	The handover of sovereignty of HK from the United Kingdom to China marked the end of the colonial era of HK	Political
	Asian currency turmoil triggered by the floating of Thai Baht	HSI once dropped over 20%; finally the HK Government intervened the market and bought about HK$120 billion worth of shares to stabilize the stock market	Economic
1998	Property market downturn and worst economic recession since 1961	The Chief Executive of HK announced the building of 85,000 flats per year, causing the downturn of property market and the economic recession	Economic
	Stressful summer	Very large net effective temperature index was observed in summer in HK	Atmospheric
2000	HSI reached all-time high	At the peak of the dot-com bubble, the HSI was driven to all-time high in HK	Economic
	Downturn of technology & internet stocks	The burst of the dot-com bubble led to the downturn of the technology and internet stocks in HK	Economic
2001	September 11th incident	A terrorist attack occurred in the US, leading to a minor impact on frequent flyers in HK who worried about terrorist attack on broad	Political
	China admitted as member of World Trade Organization (WTO)	After years of negotiation, China was admitted as member of WTO, which requested its members for economic liberalization and deregulation	Economic
2003	Outbreak of Severe Acute Respiratory Syndrome (SARS)	HK was one of the places most badly hit by the SARS epidemic and the tourism industry was seriously affected as the World Health Organisation issued travel advisory (avoid travel to HK) for a long period	Social/ Economic
	Government announcement of a HK$11 billion package to stimulate economy	To restore the HK economy, the HK Government launched the Individual Visit Scheme for mainland tourists, offered income tax rebate, reduced sales tax and business levies and offered loan scheme for industries which were affected by the SARS outbreak	Economic
	Signing of the Closer Economic Partnership Arrangement (CEPA) between Hong Kong and mainland China	CEPA was one of the policies which helped to recover the HK economy; selected service sectors in HK were allowed to enter into the mainland China market and goods of HK origin importing to mainland China enjoyed tariff free treatment	Economic
2005	Change of the Chief Executive of the HKSAR Government	The Chief Executive of HK, Tung Chee-hwa, resigned before his term of 5-year-service and was replaced by Donald Tsang	Political
	Hosting the WTO 6th Ministerial Conference	Hosting the WTO Ministerial Conference was considered as an international event for HK, but the conflict between the Korean protesters and the HK Police sparked social controversy	Political

HK: Hong Kong; US: United States; HSI: Hang Seng index; WTO: World Trade Organisation; SARS: severe acute respiratory syndrome; CEPA: closer economic partnership arrangement.

Male oldest old

For the male oldest old, the mortality rate increased sharply in 1978 and remained at high values until 1980. This period coincided with the occurrence of the second oil crisis, when the Hong Kong economy was likely affected in one way or another. People would be expected to have a lower sense of control during this period and excess mortality might follow. In 1981, the mortality rate experienced the sharpest drop over 30 years, suggesting that previous stressors were removed.

The mortality rate rose tremendously in 1982, a year when the property market downturn occurred. This effect would be more direct than the 1970s oil crisis because it affected the local economy directly. Besides financial insecurity, there was political instability around this time. The confidence in the future of Hong Kong dropped dramatically as the dispute over the sovereignty of Hong Kong started [36]. All these posted challenges to the adaptation capacity of the elderly. To make matters worse, the winter in 1982 was very severe. The excess mortality might be associated with the inability of the oldest old to withstand the combination of these stressors.

The drop of mortality rate in 1983 and 1984 was much smaller than the drop in 1981. This might suggest existing stressors were not fully removed or new stressors were emerging. First, uncertainty about the political and economic future of Hong Kong continued until the signing of the Sino-British Joint-Declaration in 1984. Second, new socioeconomic stress was likely caused by uncertainty about fluctuations in the domestic currency before the linkage of the Hong Kong dollar to the US dollar. Third, extreme weather conditions occurred in both the summer and the winter of 1983, which was even worse than that in 1982. The only stressor that disappeared was property market downturn, and the positive effect of its removal was so prominent that, even though several other stressors were present, the mortality rate still managed to go down.

The mortality rate experienced a sharp increase in 1996. This could possibly be due to the approaching of 1997, the year when the sovereignty over Hong Kong was to be handed over to the Government of the People's Republic of China. A sense of uncertainty filled the atmosphere, which was manifested in an extended wave of mass emigration during the late 1980s and the early 1990s. For seniors who had emigrated from mainland China when the political regime changed in 1949, the fears of ‘déjà-vu’ might have been projected to the 1997 hand-over and contributed to a worsening of the sense of uncertainty. Given that the lack of social support could weaken the elderly's ability to withstand environmental stressors [12] and that the emigration of close relatives was found to have the effect of reducing the caring networks of the elderly [37], all these factors could aggravate the situation.

The mortality rate increased sharply again in 1998. It was the second time that a property market downturn coincided with excess mortality. Other socioeconomic stressors such as the occurrence of the worst economic recession since 1961 and the Asian currency turmoil as well as the weather stressor from the summer of 1998 also contributed. The mortality rate remained at high values until 2000. This might be related to the socioeconomic stress being brought forward from 1998. Again, the sharp decline in mortality rate in 2001 might be due to the elimination of various stressors from previous years.

A slight increase in the mortality rate was observed in 2003. This coincided with the outbreak of SARS. During the outbreak of SARS, the Hong Kong economy was badly hit. In addition, the fear of getting infected actually destabilised Hong Kong society in different ways. Some researchers even found that social disengagement and mental anxiety at the time of SARS probably resulted in an exceptionally high rate of suicide deaths among the elderly [31]. The increase in mortality rate was less than expected, suggesting that the protective effects of the various economic stimulation programs, including the signing of the Closer Economic Partnership Arrangement, probably helped to modify the risk.

Contrasting with the female oldest old

The mortality curve of the males fluctuated a lot, whereas the mortality curve of the females was much smoother. It might be that females were less affected by environmental stressors. A sudden jump was observed in the female mortality rate in 1983. The direction of change was opposite to that for males. As discussed in the previous section, there were various environmental stressors acting in 1983. For males, the decline in mortality rate might be associated with the removal of environmental stressors, notably the property market downturn of 1982. Assuming females were not affected as much by the environmental stressors in 1982, it would be reasonable to observe an increase rather than a decline. After the environmental stressors in 1983 were removed, the mortality curve followed the previous downward trend.

As in the case of males, females experienced a sharp increase in mortality rates in the years 1996 and 2003, suggesting that the environmental stressors acting in 1996 and 2003 were likely to affect both males and females. In 1996, the uncertainty about the 1997 handover was a major stressor, whereas in 2003, the key stressor was the SARS epidemic. Although literature suggested that the SARS mortality rate was higher for the male than for the female [38], the increase in all causes mortality rate of female in 2003 was, on the contrary, larger than that of the male. This might suggest the effect of SARS was beyond the infection itself, but rather its socioeconomic effects. It seemed that without the direct effect of an economic downturn, the effects of other socioeconomic and political stressors were similar for both males and females.

Discussion

It appeared that dramatic local economic setbacks, political instability and stressful weather conditions could possibly be associated with excess male oldest old mortality. On the other hand, the effect of these stressors on the female oldest old mortality rate was not so prominent. The above qualitative analysis only serves as a starting point for more in-depth investigation. It by no means indicates that a causal relationship is being established.

The findings suggested that men seemed to be more vulnerable to socioeconomic and political events than do women. This might be because of the marked gender difference in the older Chinese generations, in that men were expected to be educated, work and earn money to provide for the family. Women were viewed as not needing to be educated and to work outside, but to raise a family and look after everything at home. In this regard, the majority of elderly women aged 70 years and above has not had any education, and it was not until the 1960s that women were paid equal salary for equal work. This attitude may have persisted to old age, when the responsibility for decisions and financial matters still rested with men. Recent study provided evidence that Chinese men were more anxious about their finance than did women [39]. Nevertheless, the reason for the gender difference has to be further investigated.

The causes of death might provide additional information on our analysis. It was observed that on average, about 62% of all deaths among the oldest old was related to circulatory and respiratory systems (ICD-9 390–519; ICD-10 I00-I99 and J00-J99), whereas for the younger elderly (aged 65 to 84), such percentage was only about 34%. This might account for the smoother mortality curves of the younger elderly population, which appeared to be less sensitive to key socioeconomic and political events.

Taking a closer look at the oldest old, deaths related to circulatory system and respiratory system accounted for 54 to 65% of all deaths in the male and 55 to 67% of all deaths in the female during the period 1977–2006. The pattern of fluctuations in the proportion of deaths related to respiratory systems of the male followed that of the female closely, except sharp increases were observed in 1985 and 2003. On the other hand, the patterns of fluctuation in the proportions of death related to circulatory systems had greater differences between the male and the female. It appeared that the gender difference in the sensitivity to key socioeconomic and political events might be related to problems in circulatory systems. A recent study in women with stable coronary heart disease showed that high economic stress was associated with an upregulation of the inflammatory process, which forms the pathogenetic basis for atherosclerosis [40]. This could explain the higher mortality from circulatory systems during economically stressful period. Nevertheless, more research is needed to determine the underlying pathogenesis.

For socioeconomic and political events that emerged over a short time period, their effect could be shown more obviously with an increase in the mortality curve. For longer lasting events like the mass wave of emigration during the 10-year period preceding 1997, they might have implications related to the caring of the elderly and hence affect mortality rates. However, these effects would not be easily identified.

For international comparison, a specific event – the September 11 terrorist attack in the United States in 2001 – is presented here. The male oldest old mortality rate showed a monotonic decreasing trend from 2000 to 2003. However, the rate of decrease in 2002, which was the year following the event, was lower than that in other years. It might suggest that the effect of the traumatic event moderated the decreasing trend. In contrast, key events in Hong Kong were prominent enough to bring the mortality rate up. Other studies have shown that a sense of coherence and adaptation to social adversity was strongly associated with morbidity and mortality outcomes [11],[41],[42]. Therefore, further research is recommended to analyse how cultural, environmental or upbringing differences might affect the coherence and coping skills of Hong Kong's seniors and account for the difference in the effect of stressful events on mortality.

According to the weather-related stress indices obtained from the Hong Kong Observatory, the years 1977, 1983 and 1998 had the most stressful summers, whereas the years 1982, 1983 and 1984 had the most stressful winters during the period 1977 to 2006. A sharp increase in mortality rate was only observed for males in 1982 and 1998 and for females in 1983. It appeared that the effect of adverse weather conditions was not as significant as that described in the literature. It might be because the effects of the socioeconomic and political events and adverse weather conditions cancelled out each other. More detailed research would be required.

One of the limitations of our study is that an observational study was used. The identified association might not necessarily be the cause of increased or decreased mortality rates. Other possible factors including air pollution were not examined in this study because many meteorological condition indicators have only been compiled recently. In addition, the combined effects of socioeconomic and political events and adverse weather conditions, which may have opposite effects on mortality rates, were not examined in this study. The results presented are suggestions on possible relationships between all-cause mortality and putative effect of environmental stressors. Although the events selected may appear arbitrary and subjective, these were events that had great impact on Hong Kong society from the frequency of media reports and discussions, on television, newspapers and radio. These were major events that affected all levels of society. Given the influence of psychosocial impact on health through the neuroendocrine system [26],[27],[43], an association may not be unexpected. For example, major fluctuations in the financial markets affected all levels of society in terms of disposable income, employment opportunities, particularly in the entertainment and food and beverage industries. The end of British colonial rule caused universal anxiety and widespread emigration efforts, with those remaining feeling trapped. Families were disrupted and some were left behind in old age homes, or children sent off to another country while parents remained behind for a time to earn income. Although these experiences are difficult to quantitate, they were nevertheless very palpable in the community. To analyse associations further, analyses with cohort studies subdividing stressors according to different types and the ability to impact the whole population or subgroups of the population would be needed. Furthermore, potential confounding factors such as changing health service provisions, such as the availability of techniques such as percutaneous transluminal coronary angioplasty in the treatment of coronary artery disease, which may affect mortality from coronary heart disease, could be taken into account.

To conclude, oldest old mortality rates were likely to be associated with environmental stressors, including socioeconomic and political events and adverse weather conditions. Men appeared to be more susceptible to these risk factors than did the female. More care and attention should be given to men in the oldest old age group, in particular, during stressful periods. A cohort study would be useful to study these stressors in greater detail. For researchers using life-event checklists, the effects of socioeconomic and political events should be included in the analysis so as to present a more comprehensive picture of all the stressors that an individual might be exposed to.

Acknowledgements

This study is part of the project entitled ‘CADENZA: A Jockey Club Initiative for Seniors’ funded by The Hong Kong Jockey Club Charities Trust.