Health status of workers approximately 60 years of age and the risk of early death after compulsory retirement: A cohort study

Abstract Objectives The increasing number of working elderly people has enhanced the importance of workplace health promotion activities. We investigated the association between the health status of workers approximately 60 years of age and the risk of all‐cause mortality after compulsory retirement in Japan. Methods The 2026 participants (1299 males and 727 females) had retired from a metal‐products factory at ≥60 years of age. Baseline health examinations were conducted at 60 years of age and included questions about medical history and lifestyle factors; the participants also underwent a physical examination. The participants were followed up annually by mail for an average of 7.4 years. The association between health status at age 60 years and the risk of all‐cause mortality was assessed by Cox proportional hazards regression analysis. Results During the study, 71 deaths were reported. The age‐ and sex‐adjusted hazard ratio (HR [95% confidence interval]) for all‐cause mortality was higher for males (HR, 3.41 [1.73‐6.69]) compared with females, participants with a low body mass index (<18.5 kg/m2; HR 3.84 [1.91‐7.73]) compared with normal body weight, smokers (HR, 2.63 [1.51‐4.58]) compared with nonsmokers, and those with three or more of four metabolic abnormalities (obesity, high blood pressure, dyslipidemia, and glucose intolerance) (HR 2.29 [1.04‐5.02]) compared with no metabolic abnormalities. The associations were unaffected by adjustment for these factors. Conclusion Maintenance of an appropriate body weight, smoking cessation, and elimination of metabolic syndrome are required for older workers to prevent early death after retirement.


| INTRODUCTION
In Japan the retirement age is 60 years, and 79% of companies comply with the uniform-age retirement system. 1 The proportions of elderly in the labor force in 2015 were 64% (early 60s) and ~43% (late 60s). 2 Furthermore, approximately 70% of people wish to continue working after 65 years of age. 3 Employment of retiring older workers is needed by both employers and employees, and enterprises with compulsory retirement at <65 of age are required to provide continuous employment until age 65 years.
Because the prevalence of lifestyle-related diseases increases after middle age, healthcare for people around the age of retirement is important. In Japan, medical checkups and the health-guidance system provided by health insurers, and the Collabo-Health healthcare system provided by employers in collaboration with health insurers, promote maintenance of the health of middle-aged and elderly workers. Furthermore, municipal healthcare providers regard healthcare for older people around the age of compulsory retirement as important, because following compulsory retirement, elder retirees join the National Health Insurance system provided by municipalities. The demand for healthcare services for older people in communities in cooperation with the work site has increased.
Previous studies have indicated that the risk of mortality for healthy retirees is associated with the age of retirement, [4][5][6] social engagement, 7,8 relative poverty, 8 and subjective life expectancy. 9 Changes in lifestyle after retirement may also affect mortality. Previous studies have indicated that physical activity, [10][11][12] particularly leisure time physical activity, 13,14 increases after retirement. However, alcohol intake 11,14 and the prevalence of lifestyle diseases 12 remain unchanged after retirement, and the effect of retirement on smoking is controversial. 11,12,[14][15][16][17] Retirement may also increase depressive symptoms. 18 The transition to retirement can have a major influence on people's health behaviors, health, and quality of life, and could also be an opportunity to intervene with health-promoting activities. However, the types of lifestyle interventions that are effective in improving the longevity of older workers around the age of compulsory retirement are not fully established. In this study, we evaluated the risk of early death after retirement among former employees of a factory in Japan who retire at approximately 60 years of age.

| Participants
The participants were retirees from a factory that produces zippers and aluminum sashes in Toyama Prefecture, Japan. In the factory, 46% of the employees were white-collar workers (administrators, managers, clerical workers, and professional workers) and 53% were blue-collar workers (operation of machinery, processing or construction of aluminum products, and other manual work). Details of this study population have been reported previously. [19][20][21] The retirement age at the factory is 60 years. Employees who went through mandatory retirement between 2003 and 2016 were enrolled. Baseline data from a health examination at approximately 60 years of age (58-62 years) were obtained retrospectively. Among the 2061 potential participants (1331 males and 730 females), 35 (1.6%) were excluded because of death (n = 18), missing baseline health data (n = 14), or no response to the annual follow-up survey (n = 3). Therefore, a total of 2026 individuals (1299 males and 727 females) were enrolled in this study.

| Baseline examination
The baseline health parameters of the participants before retirement at approximately 60 years of age (58-62 years) were evaluated. The Industrial Safety and Health Law in Japan requires employers to carry out annual health examinations for all employees. The annual health examination is carried out by trained staff and includes a medical history, physical examination, anthropometric measurements, and measurement of fasting plasma glucose (FPG), HbA1c, and serum lipid levels. Height was measured without shoes to the nearest 0.1 cm using a stadiometer. Weight was measured with participants wearing only light Conclusion: Maintenance of an appropriate body weight, smoking cessation, and elimination of metabolic syndrome are required for older workers to prevent early death after retirement.

K E Y W O R D S
all-cause mortality, cohort study, compulsory retirement, elderly workers, risk factor | 3 of 9 SAKURAI et Al.
clothing and no shoes to the nearest 0.1 kg using a standard scale. Body mass index (BMI) was calculated as weight/ height 2 (kg/m 2 ). Blood pressure (BP) was measured using a mercury sphygmomanometer after the participant had rested for 5 minutes in a seated position. The FPG level was measured enzymatically using the Abbott Glucose UV Test (Abbott Laboratories). The HbA1c level was measured by high-performance liquid chromatography using a fully automated analyzer (Kyoto Daiichi Kagaku). The total cholesterol and triglyceride levels were assessed by enzymatic assay, and the high-density lipoprotein cholesterol level was measured using a direct method. The low-density lipoprotein cholesterol level was calculated using Friedewald's formula when the triglyceride level was <400 mg/dL. 22 A questionnaire was used to evaluate the voluntary healthrelated behaviors of alcohol consumption, smoking, and exercise habits. A self-administered questionnaire was used to collect information regarding the histories of hypertension, dyslipidemia, and diabetes. High BP, dyslipidemia, and a high FPG level were defined using the Japanese criteria for metabolic syndrome. 23 High BP was defined as a systolic BP ≥130 mmHg, a diastolic BP ≥85 mmHg, or the use of antihypertensive medication. Dyslipidemia was defined as a serum triglyceride level ≥150 mg/dL, a high-density lipoprotein cholesterol level <40 mg/dL, or the use of medication for dyslipidemia. A high FPG level was defined as an FPG level ≥110 mg/dL, an HbA1c level ≥6.0%, or the use of antidiabetic medication.

| Follow-up survey
There is an organization for retirees from the factory who have completed at least 35 years of service; more than 90% of retirees are members. We obtained from the organization annually a list of the members who had died during the previous year. Additionally, we mailed a questionnaire survey annually to those retirees who retired after 1990. The questionnaire inquired about various measures of health status, such as cardiovascular disease and treatment of lifestyle-related diseases. We mailed the questionnaire beginning in 2003, when the number of recipients was 1204; this number had increased to 3394 in 2017. The mean response rate was 87.6% (range, 65.7-91.9%). The death of the participant was confirmed by a response from a family member.

| Statistical analysis
To analyze all-cause mortality, the standardized mortality ratio (SMR) was calculated after adjustment for age using the age distribution and death rate per decade of the general Japanese population during the observation period as the standard population. The associations between baseline characteristics and all-cause mortality were evaluated by Cox's proportional hazard model after adjustment for age and sex, after adjustment for variables significantly associated with all-cause mortality in the age-and sex-adjusted models, and after adjustment for alcohol drinking and exercise habits. As a sensitivity analysis, we evaluated the associations between baseline characteristics and all-cause mortality among males and after exclusion of participants who died within 3 years of follow-up.

| RESULTS
The baseline characteristics of the participants are shown in Table 1. The mean (standard deviation, SD) age of the participants at baseline was 59.7 (0.7) years for males and 59.4 (0.8) years for females. During the follow-up (total, 15 044 person-years; mean, 7.4 years; range, 1-13 years), we documented 71 deaths (61 males and 10 females); 54 were reported by retiree organizations and 17 by the participants' families. The all-cause mortality rate of the participants was 4.0/1000 person-years.
The standardized mortality ratio (95% confidence interval) for all-cause mortality of the participants was 0.60 (0.54-0.66) for males and 0.41 (0.36-0.46) for females. These values are significantly lower than those of the general population of Japan.
We evaluated the association between health status before retirement and the risk of death after retirement ( Table 2). The HR for all-cause mortality after adjustment for age and sex was significantly higher for males, those with a BMI <18.5 kg/m 2 , and current smokers. Obesity, high BP, dyslipidemia, and glucose intolerance were not significantly associated with the risk of death. However, the number of complicated metabolic abnormalities was associated with the risk of death (HR 2.29 for three or more metabolic abnormalities compared with no metabolic abnormality).
After adjustment for the variables significantly associated with all-cause mortality, the BMI, smoking status, and number of complicated metabolic abnormalities were found to be independently associated with the risk of all-cause mortality (Table 3, model 1). These associations were unaffected by adjustment for other lifestyle factors, for example, alcohol drinking and exercise habits (model 2).
The results of the sensitivity analysis are shown in Table 4. The results for males were similar to those of all participants. Evaluation of the factors associated with the risk of mortality among females was hampered by the small number of events. Because the participants who died soon after retirement might have suffered from a disease, such as cancer, which could have affected the baseline examination, we excluded those participants followed up for <3 years. Among the 1819 participants followed up for >3 years, we documented 59 deaths (mortality rate, 4.0/1000 person-years). A low BMI, current smoking, and a large number of complicated metabolic abnormalities were associated with a significantly higher risk of mortality.

| DISCUSSION
In this cohort study of retirees approximately 60 years of age, the age-adjusted mortality rate was approximately 40% lower for males and 60% lower for females compared with those of the general population in Japan. Being underweight, smoking, and having a large number of complicated metabolic abnormalities at approximately the age of retirement (60 years) were significantly associated with early death after retirement. Therefore, workplace health education for employees approaching retirement age, to promote maintenance of an appropriate body weight, smoking cessation, and elimination of metabolic syndrome, could prevent early death after retirement.
The mortality rate of the participants was lower than that of the general population in Japan, possibly related in part to the healthy-worker effect. 24 That is, workers typically have a lower overall mortality rate than that of the general population because severely ill and chronically disabled individuals tend not to be employed. In addition, the study participants may be healthier than the general population because they continued working until retirement age. Furthermore, the participants were employees of a relatively large company, who reportedly are healthier than those of small-to-medium-sized enterprises 25 due, for example, to a greater emphasis on health promotion activities. Indeed, beginning in 1980, the subject company conducted disease prevention and health promotion activities in cooperation with occupational physicians and publichealth nurses. These factors may explain the relatively low mortality rate of the participants.
The risk of early death after retirement was higher among males, participants with a low BMI, current smokers, and those with a large number of complicated metabolic abnormalities at approximately retirement age (60 years). These results are concordant with previous reports from Japan that a low BMI, 26 smoking, 27 the number of metabolic abnormalities, and metabolic syndrome 28,29 are associated with a higher risk of both all-cause and cardiovascular-related mortality. Healthcare for the working population is important to obtain good health so that they can continue to work at a greater age. Similarly, the results of this study indicated that healthcare for workers is important to extend a healthy life expectancy after retirement.
In addition to obesity and metabolic syndrome, a lower BMI is an important problem in older people. Obesity and metabolic syndrome are associated with cardiovascular disease, 23  another important cause of disability. 30,31 Lower BMI is associated with undernutrition, lower muscle mass, sarcopenia, and frailty, which are risks for disability. 32 Our study showed that metabolic syndrome and a lower BMI around the age of 60 years are associated with early death after retirement. Exercise instruction and nutritional support for workers to maintain ideal body weight are needed to prevent disability at a later age and to extend life expectancy. Retirement is an important turning point in life and is associated with marked changes in lifestyle. Previous studies have indicated that overall physical activity 10-12 and leisure time physical activity 13,14 increase after retirement. However, alcohol intake 11,14 and the prevalence of lifestyle diseases 12 remain unchanged after retirement. The effect of retirement on smoking is controversial. Previous studies have indicated that retirement is associated with a higher risk of increased smoking, particularly for the involuntarily retired 15 ; retirement accelerates smoking cessation 14,17 ; retirement reduces smoking rates for women but not men 11,16 ; and that smoking rates are unchanged after retirement. 12 Our results indicate that smoking is an important risk factor for early death after retirement. Retirement is a major life-course transition; however, previous studies have indicated that smoking status in retirement does not always change favorably, so more intensive health education programs for smokers around the age of retirement are needed.
Japan has a declining birth rate and an aging population. The resulting reduction in the working-age population will provide the elderly with opportunities for employment. The number of elderly individuals with chronic illnesses and disabilities will increase in the future, emphasizing the importance of health promotion and disease prevention activities for elderly workers for both employers and providers of employment-based health insurance. The Collabo-Health healthcare system provided by employers in collaboration with health insurers promotes maintenance of the health of middle-aged and elderly workers. Additionally, because healthcare services for older people after retirement are provided by local municipalities, regional and occupational cooperation is important to provide continuous healthcare services for older workers around the age of retirement.
The strength of this occupational cohort study is that the participants were followed up after retirement. In general, evaluation of mortality and the incidence of cardiovascular diseases after retirement is problematic. We obtained information on mortality and changes of address from the retiree organization and by conducting an annual mail survey, which had a response rate of 86.7%. This study also has several limitations. First, we did not evaluate the risk of cause-specific mortality because we lacked data on the causes of death. Second, 13.3% of the participants did not respond to the annual mail survey, which was the only means of obtaining mortality data from non-members of the retiree organization. Participants who did not respond to the annual mail survey were censored, which may have resulted in underestimation of the mortality rate. Third, the number of deaths observed in this study was relatively small, which reduced the statistical power of the analysis. For example, the mortality rates for the highest categories (blood pressure, dyslipidemia, and FPG/HbA1c) were relatively high, although no significant differences were observed (Table 2). However, the number of complicated metabolic abnormalities was significantly associated with mortality (Table 3), and the results indicated that control of metabolic abnormalities and their accumulation is important to prevent early death after retirement, although no metabolic abnormality was significantly associated with mortality. Fourth, we did not have data on socioeconomic factors or changes in lifestyle after retirement. Some socioeconomic factors, such as poverty and social engagement, have been reported to be associated with mortality in older people. 7,8 Changes in lifestyle after retirement may also affect mortality. However, our results will be helpful to select highrisk workers around the age of retirement for intervention to prevent early death.
In conclusion, a low BMI, smoking, and a large number of complicated metabolic abnormalities around the age of retirement significantly increased the risk of death after retirement. Retirement is an important turning point in life and a good chance to change lifestyle. To prevent early death after retirement, maintenance of an appropriate body weight, smoking cessation, and elimination of metabolic syndrome are required for workers around the age of retirement. Additionally, regional and occupational cooperation are needed for continuous health education activities in older workers and retirees.