Mental Depression and Death in Elderly Persons

To investigate the relationship between mental depression and death among elderly persons, a prospective study was conducted. 2,166 inhabitants aged from 60 to 74 years in the Hidaka district of Hokkaido Prefecture, Japan were employed. From December 1990 to January 1991 we estimated the degree of depression of the subjects, using the self-rating depression scale (SDS) developed by Zung. The subjects were classified into 3 groups according to the average SDS score ( Group A, <2.00; Group B, 2.00-2.39 and Group C>-, 2.40), and were followed up periodically until February 1995 to confirm whether they were still alive. The highest mortality was noted in Group C which consisted of those who had severe depression. Their mortalities for cancer, pneumonia and suicide were significantly high. After the adjustment of age, number of current diseases, smoking state and sex, a similar tendency was noted. Mental depression increased mortality of the aged. Part of this mechanism might be explained by the suppression of immunological resistance. J Epidemiol, 1997; 7 : 210-213.

The number of elderly people is rapidly increasing in Japan.It is important for them to lead life in physically and mentally good condition.Thus, at present, the relation between mental status and physical condition is attracting much attention.Murphy et al. 1)I reported that the mortality of those who suffered from depression or anxiety was by about 1.5 times higher than in those who did not.
Employing the self-rating depression scale (SDS) developed by Zung 2), we investigated the relation between mental depression and death in elderly persons.

SUBJECTS AND METHODS
A total of 2,623 inhabitants aged from 60 to 74 years in the Hidaka district of Hokkaido Prefecture, Japan were systematical-randomly selected from the register of inhabitants in 1990.This district, which is an area of primary industry, is located in the southwestern part of this prefecture (from 43° N, 143° E to 42° N, 142° E).The present subjects accounted for about 22% of the 12,038 inhabitants of this district aged from 60 to 74 years.
From December 1990 to January 1991, we sent the subjects a questionnaire, inquiring about their general health state, eating habits, human relationships, current diseases for which they were receiving treatment, the degree of mental depression, and so on.In this paper we refer exclusively to the relation between depression and death.

1.Evaluation of mental depression
The SDS was introduced to Japan over 20 years ago.We employed the version of the SDS used by Fukuda et al. 3) with some modification of its language.The SDS consists of 20 questions and one of 4 scores is allotted to each answer, depending on the degree of depression [ 1 (none), 2 (slight), 3 (intermediate), and 4 (severe)].We employed the average of 20 answers as the "SDS score".

2.The number of current diseases
In the questionnaire we presented 9 categories of disease (diseases of the digestive system, high blood pressure, heart disease, liver disease, respiratory organ disease, diabetes melli-tus, cerebrovascular disease, severe injury and others) and asked the subjects to mark the names of diseases for which they were receiving treatment at the time of survey.

3.Confirmation of being alive or dead
In January 1991 we started to follow them up periodically to confirm whether they were still alive.If a subject had died, the exact cause of death was checked by reviewing the death certificate.

4.Statistical procedure
Chi-square test and t-test were employed for statistical analysis.The 95% confidence interval (CI) of mortality was calculated using F-distribution.

RESULTS
A total of 2,166 (82.6%) of the present subjects gave eligible answers.Their average SDS score was 1.85.
Okimoto et al. v employed two average SDS scores, 2.00 and 2.40, (or total score 40 and 48) as cutoff points for the detection of slight and severe depression, respectively.We divided the subjects into 3 groups depending on the score [Group A (not depressive), <2.00 ; Group B (slight -intermediate depression), 2.00-2.39 ; and Group C (severe depression), >_ 2.40].

1.Mortality
There was no significant difference in age at the time of survey among the 3 groups.Mortality increased as the SDS score went up.The mortality of Group C was 6.6 times as high as that of Group A. This difference was significant (Table 1).

2.Mortality of males and females
Mortality of males was higher than that of females in each of the groups.Males were more likely to die than females, even with the same degree of depressive state.The difference between the sexes increased as the SDS score increased.In Group A, the mortality of males was 1.56 times as high as that of females.But in Group C, it was 3.95 times as high (Table 1).

3.Mortality for various diseases
At present in Japan, cancer, heart disease and cerebrovascular disease are the three major causes of death.These three accounted for about 60% of all Japanese deaths in 1993 9 The mortality for cancer in Group C was 2 to 5 times as high as that of Groups A and B. The difference between Group A and Group C was significant.That for pneumonia in Group C was about 4 times as large as that of Group B. No one committed suicide in Groups A and B. The mortality for cerebrovascular disease also increased, though not significantly.The increase in mortality for ischemic heart disease was small (Table 2).In general, sex and age are related to mortality.When a person has a disease, it may influence life expectancy as well.It is well known that smoking brings about various diseases.However, even when age, the number of current diseases, smoking state, and sex were adjusted for, the risk ratio for death became higher as the score increased, though there were a few exceptions (Table 3).In logistic regression analysis, employing these 4 factors and the SDS score (a continuous varible) as explanatory variables, the SDS score remained significant (Table 4).

DISCUSSION
Total mortality ran parallel to the severity of depression.The risk ratio for death increased as the SDS score went up, almost regardless of age, the number of current diseases, smoking state, and sex.Males with severe depression were at the highest risk.
In Group C mortality was high for cancer and pneumonia.These diseases are strongly related to immunological resistance.On the other hand, the mortality for ischemic heart disease, whose etiology may be less related to the immunological system, did not increase significantly.Depression might weaken immunological resistance, leading to the occurrence of diseases such as cancer and various infectious diseases.Shekelle et al. 6)reported that patients with depression had a higher risk for cancer death.Many reports suggest that the depressive state works disadvantageously on immunological function [7][8][9][10][11].In this study subjects with severe depression were more likely to die than those without it, when they had the same number of diseases at the time of survey.It is also possible that depression accelerates the development of diseases through weakening immunological system and shortens the survival period.Thus, in order to maintain the health of the aged, it is important to remove psychological circumstances bringing about depression and to establish a system of support for those who are depressive, especially male patients.

CONCLUSIONS
Mental depression increased mortality of the aged.In the group of severe depression, the mortalities of cancer and pneumonia were high.The mechanism by which this occurred might, in part, be explained by the suppression of immunological resistance.

Table 3 .
Risk ratios for death by age, number of current disease, smoking state, and sex (number of dead : alive persons in parentheses).

Table 4 .
Logistic regression analysis with regard to age, number of current disease, smoking state, sex, and SDS score.