Impact of smoking habit on medical care use and its costs: a prospective observation of National Health Insurance beneficiaries in Japan

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1 International Epidemiological Association 2001 Printed in Great Britain International Journal of Epidemiology 2001;30: Impact of smoking habit on medical care use and its costs: a prospective observation of National Health Insurance beneficiaries in Japan Yoko Izumi, Ichiro Tsuji, Takayoshi Ohkubo, Aya Kuwahara, Yoshikazu Nishino and Shigeru Hisamichi Background To quantify excess medical use associated with smoking, a large prospective cohort study is needed. The authors examined the impact of smoking on medical care use in a large population-based cohort with an accurate data collecting system in Japan. Method The data were derived from a 30-month prospective cohort study of National Health Insurance beneficiaries aged years living in a rural Japanese community. The smoking habit of beneficiaries was assessed in a baseline survey at the end of Medical care use and its costs were monitored by linkage with the National Health Insurance claim history files since January Results Male smokers incurred 11% more medical costs (after adjustment for age, physical functioning status, alcohol consumption, body mass index and average time spent walking) than never smokers but for female smokers and never smokers the costs were almost the same. This difference was mainly attributable to increased use of inpatient medical care among smokers, especially in males, where per month cost of inpatient care was 33% higher in smokers. Age-group specific analysis in men showed that excess mortality and excess medical cost ratio for smokers peaked in those aged years. Conclusions Smokers consume excess medical care. Among the population aged 45 years and over, about 4% of total medical costs were attributable to smoking. To pursue both better health and lower medical costs for the nation, a comprehensive programme to reduce tobacco use is needed. Keywords Cohort study, smoking, medical costs Accepted 10 October 2000 Smoking has proven to be a major cause of diseases such as cancer, heart disease, and cerebrovascular and respiratory disease. 1,2 The health hazards of smoking lead smokers to consume more medical resources than non-smokers, and thus greater medical expenditure. Rice et al. 3 found that the number of days spent in hospital and the number of visits to physicians were significantly higher among smokers. On lifetime medical expenditure, Hodgson 4 showed that the impact of smokers higher medical care use outweighed shorter life expectancy; Department of Public Health, Tohoku University School of Medicine, Sendai, Japan. Correspondence: Yoko Izumi, Department of Public Health, Tohoku University School of Medicine, 2 1 Seiryo-machi, Aoba-ku, Sendai, Japan. BZE16213@nifty.ne.jp smokers having an excess lifetime medical expenditure of 43% for males and 29% for females. In these studies, the relationship between smoking habit and medical care use was analysed using cross-sectional survey data, while long-term cumulative costs attributable to smoking were estimated only by theoretical models. Model analyses were limited because they did not fully examine the interrelationship between smoking and confounding factors such as age, health status and health-related behaviours. Although several prospective observational studies have investigated this issue, the sample sizes were too small to allow statistical adjustment or stratified analysis. The effect of smoking on medical care utilization and its costs might be more serious in Japan, where the smoking rate is much higher than in Western countries. According to a national survey, 52.7% of adult men and 11.6% of adult women were 616

2 IMPACT OF SMOKING ON HEALTH CARE USE 617 current smokers in Japan in However, the relationship between smoking and medical costs in Japan has not been fully investigated yet. The objective of the present study is to investigate the impact of smoking upon medical care utilization and its costs based on a large prospective cohort study in Japan. In this cohort study, we conducted a baseline survey of health-related lifestyle on a representative sample in the community (N = ) in Medical care utilization and its costs have been followed among the subjects by linkage with the National Health Insurance Claim Files, which covered almost all medical care. Because the unit of analysis in the present study is the individual subjects unlike in most of the previous studies, we are able to control for confounding variables. Thus it provides us with the best data set for investigating the relationship between smoking and medical care use. Methods Study design The present data were derived from the Ohsaki cohort study. 6,7 Subjects were all National Health Insurance (NHI) beneficiaries, aged years, living in the catchment area of the Ohsaki Public Health Center, Miyagi Prefecture, north-east Japan. The NHI is a community-based health insurance for farmers, the self-employed, pensioners, and their dependants. The study area is a typical rural area and the main industry is agriculture. Overall NHI covered 55% of the population aged years. Details of the study design and the characteristics of the study subjects have already been published. 6,7 This study has been approved by the Ethical Committee of Tohoku University School of Medicine. We conducted a baseline survey about physical function and health-related lifestyle between October and December Trained survey personnel visited the subjects and informed them of the survey objectives and their freedom to decline, and asked them to complete the questionnaires. Of eligible individuals, (95%) responded and formed the study cohort. The baseline survey included questions on smoking habit, and the subjects were classified into three categories: current smokers, ex-smokers, and never smokers. For current and ex-smokers, per day cigarette consumption and age at starting smoking were also asked. For physical functioning status, we used the six-item physical function measure of the Medical Outcome Study (MOS) Short-form General Health Survey. 8,9 We have been collecting data on medical care use and its costs for each subject from the monthly NHI claim history files of the Miyagi NHI Association since January In the present study, claim history files from January 1995 to June 1997 (30 months) were analysed. When a beneficiary was withdrawn from NHI because of death or emigration, the date and reason were entered on the NHI withdrawal history files. Both NHI claims and withdrawal history files were linked with our baseline survey data file. Emigration includes moving to areas outside of the catchment area of Ohsaki Health Center and transfer to other insurance. When a beneficiary was withdrawn from the NHI, we stopped following up that person even if he or she re-enrolled in NHI. Study subjects Among the respondents of the baseline survey in 1994, we excluded 774 subjects because they had been withdrawn from the NHI before 1 January 1995 when we started prospective collection of NHI claim history files. We then excluded 7845 subjects with missing information on smoking habits. Thus we analysed subjects. Among these, two male subjects showing extremely high per month medical costs were excluded, so that (male ; female ) were finally analysed. Outcome variables We examined the impact of smoking habit on mortality, medical care use and its costs. Medical care use and its costs were indicated as hospitalization rate, visit rate, number of hospital days, number of physician visits, and medical costs (total, inpatient, outpatient). Inpatient medical costs included almost all medical treatment at hospitals, such as diagnostic tests, medication, surgery, supplies and materials, physician and other personnel costs, but not hospital meal fees. Outpatient medical costs included medical treatment in outpatient clinics, prescribed drugs, and home care services provided by physicians, but not dental care. The number of hospital days, the number of physician visits, and medical costs were calculated as per capita per month indices, including all subjects and all months of observation irrespective of whether or not they had received care. We examined per month costs instead of accumulated costs through observation, because the latter indices would underestimate the medical costs of the subjects with shorter observation, i.e. the deceased or those who emigrated. Death rate was calculated as the percentage of subjects who died during the 30 months of observation. Hospitalization rate and visit rate were calculated as the percentages of subjects ever having received inpatient and outpatient care, respectively, during the 30 months of observation. For this paper, monetary values were converted into British pounds using the rate of 1 = 180 yen. Statistical analysis The impact of smoking habit on per month per capita number of physician visits, hospital days, and medical costs (total, inpatient, outpatient) were examined by analysis of covariance (SAS PROC GLM). 10 The impact of smoking habit on mortality risk was examined as the hazard ratio (HR) using a Cox proportional hazards regression model (SAS PROC PHREG). 10 The dependent variable was the number of days from 1 January 1995, to the date of death or censoring. Survivors were censored as of 30 June The odds ratios (OR) for the effect of smoking on hospitalization and physician visit, respectively, were examined using a multiple logistic regression model (SAS PROC LOGIST). 10 Tests of linear trend across amount of smoking were conducted by treating the category (never, moderate, heavy) as a continuous variable. All statistical analyses were performed separately for male and female subjects. Multivariate models included as covariates: (1) age, (2) physical functioning status (MOS scores 0 1, 2 4, 5 6), (3) alcohol consumption (never, ethanol 90 g/day, 90 g/day), (4) body mass index (weight [kg]/height [m] 2 )

3 618 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY ( 22, 22 24, 25), (5) time spent walking ( 30, 30 59, 60 min). Results Characteristics of the subjects The mean per capita medical cost for May 1995 among subjects in this cohort aged years was 106, and was comparable with the national average in the same period ( 113, as standardized to the age composition of the present cohort). 11 Of the subjects, 1117 (2.6%) had died and 3133 (7.2%) had withdrawn from the NHI before 1 July The mean period of observation was 15.8 months for the deceased and 12.8 months for those who had withdrawn. The mean per capita per month medical costs (dividing the accumulated costs by the number of months of observation for each subject) were 1125 for the deceased, 122 for those who had withdrawn, and 129 for the survivors. The deceased had costs per month nine times higher than the survivors but there was no difference between those who had withdrawn and the survivors. Smoking habit Table 1 shows the smoking habits of the study subjects. The percentages of current, ex-, and never smokers were 54.9%, 26.6%, and 18.4%, respectively, and the percentage of current smokers decreased with age, while ex-smokers increased. In females, the figures for current, ex-, and never smokers were 8.5%, 2.7%, and 88.8%, respectively. According to the national survey in Japan, 5 the percentages of current and ex-smokers were 47.9% and 27.3% in males, and 7.8% and 2.3% in females (after adjustment for age distribution), thus the present cohort showed a slightly higher smoking rate. In the present study, we treated both ex-smokers and current smokers as ever smokers, because of the similarity of the two groups. Ages at starting smoking were 23.3 years for current smokers and 23.1 years for ex-smokers (P 0.05). Daily cigarette consumption was 19.8 and 20.1, respectively (P 0.05). Number of years after quitting in ex-smokers had no relationship with adjusted medical costs (data not shown). We thus compared medical care use and its costs between ever smokers and never smokers. Table 1 Distribution of smoking habit by sex and age group Distribution of smoking habit (%) No. of subjects Current Ex- Never All ages Females All ages Medical care use and its costs in smokers and never smokers (Table 2) For males, mortality risk was significantly higher in smokers than in never smokers (HR = 1.47). A similar association was observed in females (HR = 1.26), although it was nonsignificant. Hospitalization rates were significantly higher for smokers of both sexes (OR: male 1.26, female 1.22). Number of hospital days per month per capita were significantly higher for smokers of both sexes (male: never smokers 0.50, smokers 0.64; female: never smokers 0.44, smokers 0.54). Physician visit rates were lower for smokers of both sexes but significant only in females (OR: male 0.94, female 0.74). However, per capita physician visits were not significantly different in either sex. In males, per capita per month medical costs were 170 for smokers, which was 11% higher than never smokers (P 0.01), but in females, it was 141 for smokers, almost the same as that of female never smokers. Differences in medical care costs were mainly attributable to differences in costs for inpatient care. Per month per capita inpatient costs were higher for smokers of both sexes, 33% higher in males (P 0.001) and 8% higher in females (ns). Per month per capita outpatient costs were slightly lower for smokers in both sexes. Medical care use and its costs by amount of smoking for males (Table 3) To examine the effect of smoking amount on medical care use and its costs, we employed the Brinkman Index (BI: daily number of cigarettes years of smoking) and categorized smokers into moderate smokers (BI: 1 399) and heavy smokers (BI: 400). These analyses were performed only for males, because the number of heavy smokers was small in females. There was a significant trend between BI and HR of death. Hospitalization rate increased significantly with BI. Per capita per month medical costs (total and inpatient costs) increased significantly with BI. Effect of smoking by age groups for males (Table 4) We analysed the effect of smoking on mortality risk and medical costs by 10-year age groups for males. The HR of mortality for smokers increased gradually with age and peaked at years (HR = 1.98) then dropped at years (HR = 1.21). On per capita per month medical costs for men, smokers excess cost ratio increased with age, being highest in the year age group (27% excess). Discussion In our study cohort, 54.9% of men and 8.5% of women were current smokers, while ever smokers comprised 81.5% in males and 11.0% in females. Their smoking rate and per capita medical costs were comparable to the national average. In this study, smokers incurred more medical costs than never smokers, by 11% in males, but costs were almost the same in females. This difference was attributable mainly to the increased use of inpatient medical care among smokers, especially males, where the per month cost of inpatient care was 33% higher in smokers. In outpatient care indices, the visit rate tended to be lower in smokers, but no significant differences were observed in costs.

4 IMPACT OF SMOKING ON HEALTH CARE USE 619 Table 2 Mortality, medical care utilization and its costs by smoking habit Females Never smokers Smokers P-value Never smokers Smokers P-value No. of subjects Death rate a (%) Hazard ratio b (95% CI) (NA) ( ) (NA) ( ) Hospitalization rate a (%) Odds ratio b (95% CI) (NA) ( ) (NA) ( ) Per capita per month hospital days b (95% CI) ( ) ( ) ( ) ( ) Visit rate a (%) Odds ratio b (95% CI) (NA) ( ) (NA) ( ) Per capita per month physician visits b (95% CI) ( ) ( ) ( ) ( ) Per capita per month cost b (total) ( ) Total (95% CI) (142, 165) ( ) ( ) ( ) Inpatient (95% CI) (52 71) (78 87) (48 52) (43 62) Outpatient (95% CI) (86 97) (85 90) (90 94) (82 94) a Crude rate. b Adjusted for confounding factors. Our method of data acquisition has several advantages: (1) data on lifestyle and characteristics of the subjects are available from the baseline survey, and thus adjustment can be made for confounding factors; (2) by using NHI claim history files, almost all medical costs were accurately counted; and (3) because NHI is a community-based insurance, geographical differences in access to medical care would be unlikely. Our study added some new knowledge to previously reported cross-sectional studies regarding the effect of smoking on medical care expenditure. The impact of smoking on medical care use was different between inpatients and outpatients. Smokers used outpatient care less often than non-smokers. This finding might reflect smokers low concern for their health. This aversion to seeking medical care at earlier and less severe stages of illness among smokers may result in a worse prognosis. In fact, a substantial part of the increased medical costs among smokers was attributable to the increased use of inpatient care. Thus, the mechanism of increased medical costs among smokers is twofold not only the hazardous effect of smoking on health itself, but also a worse prognosis for illness due to lack of appropriate treatment in the early stages. Second, the present study showed that, in men, excess mortality and inpatient care use and total medical cost in smokers peaked in the year age group. This is consistent with the result of Doll et al., 1 that the mortality of continuing cigarette smokers was threefold at ages years and only twofold at ages years compared with never smokers. Most of the model analyses, however, indicated that the difference in medical cost between smokers and non-smokers became larger with age. The effect of age on excess medical costs by smoking should be further studied. Our study had several limitations. First, the impact of smoking on medical costs was clear in men but not always so in women. This was because women s smoking rate (including ex-smokers) was as low as 11.0%, and the duration and amount of smoking was less than that of male smokers (data not shown). Second, the observation period in the present study was 30 months. This might be too short to take account of smokers higher mortality and the accompanying cost of terminal medical care, and might underestimate excess medical costs among smokers. As in other developed countries, medical care costs in Japan are escalating with the increasing proportion of older people in the population. National health care cost in fiscal 1996 was estimated to be 7.3% of the gross domestic product. 12 We believe that one way to better contain medical care costs is to reduce needs and demands for medical services by extending the activities for disease prevention and health promotion. 13 In Japan, where the smoking rate (including ex-smokers) is extremely high in men (74.9%) and growing in women (14.7%), 5 the impact of smoking on health and costs might be larger than in other developed countries. The populationattributable risk percentage of smoking for death in Japan is 26.0% in men and 3.7% in women, based on HR of death in the present study and the national smoking rate. We also estimated national excess medical costs caused by smoking in people aged 45 years and over. From the ever smoker : never smoker ratio of per month medical costs observed in

5 620 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY Table 3 Mortality, medical care utilization and its costs by smoking amount (Brinkman Index [BI]) for males Moderate Heavy Never (BI 1 399) (BI 400) P for trend No. of subjects Death rate a (%) Hazard ratio b (95% CI) (NA) ( ) ( ) Hospitalization rate a (%) Odds ratio b (95% CI) (NA) ( ) ( ) Per capita per month hospital days b ( ) ( ) ( ) ** ** Visit rate (%) a Odds ratio b (95% CI) (NA) ( ) ( ) Per capita per month physician visits b Per capita per month medical cost b ( ) ( ) ( ) ( ) *** Total ( ) ( ) ( ) *** Inpatient (50 69) (66 87) (76 87) *** * Outpatient a Crude rate. b Adjusted for confounding factors. * P 0.001, ** P 0.01, *** P ** (84 95) (86 98) (83 89) Table 4 Hazard ratio (HR) of death, odds ratio of hospitalization and physician visit to smokers by age groups for males Medical costs ( ) b Mortality a (HR) (95% CI) Never smokers (A) Smokers (B) Ratio (B/A) All ages 1.47 ( ) ( ) ( ) ( ) (0.90, 1.62) a Adjusted for confounding factors. b Per capita per month costs adjusted for Medical Outcome Study scores. the present study (male 1.11; female 1.00) and from national smoking rate, 3.8% of total medical costs were attributable to smoking. In the US, where the prevalence of smoking among adults is 26%, 7.1% of medical care cost was estimated to be attributable to smoking. 14 Our estimate seemed to be relatively small, but the difference in the method of estimation and definition of medical care cost should be considered. To reduce tobacco use, comprehensive programmes such as limiting tobacco advertisements and increasing tobacco excise tax to finance anti-tobacco health programmes have been proposed in several countries. 15,16 Smoking cessation programmes for current smokers, including nicotine replacement therapies, are proving to be useful and cost effective, 17,18 and insurance coverage of these programmes is advocated. 19,20 We expect that, in Japan, health policy makers and insurers could also improve and promote their tobacco control programmes in the context of health promotion and medical care cost reduction.

6 IMPACT OF SMOKING ON HEALTH CARE USE 621 Acknowledgement The study was conducted in close collaboration with the Miyagi NHI Association and the Ohsaki Public Health Center. We thank Dr Atsushi Sasaki, Director of Ohsaki Public Health Center, for managing administrative issues at the study project site. Funding for this study was supported by a Health Science Research Grant of Health Services, Ministry of Health and Welfare, Japan. KEY MESSAGES The impact of smoking on medical care use was examined in a 30-month prospective population-based cohort study in Japan (N = ). Male smokers incurred 11% more medical costs than never smokers but for female smokers and never smokers the costs were almost the same. This difference was mainly attributable to the increased use of inpatient medical care among smokers, especially in males, where per month cost of inpatient care was 33% higher in smokers. References 1 Doll R, Peto R, Wheatley K, Gray R, Sutherland I. Mortality in relation to smoking: 40 years observations on male British doctors. BMJ 1994;309: Shinton R, Beevers G. Meta-analysis of relation between cigarette smoking and stroke. BMJ 1989;298: Rice DP, Hodgson TA, Sinsheimer P, Browner W, Kopstein AN. The economic costs of the health effects of smoking, Milbank Q 1986;64: Hodgson TA. Cigarette smoking and lifetime medical expenditures. Milbank Q 1992;70: Ministry of Health and Welfare, Japan. National Nutrition Survey (Kokumin Eiyo Chosa). Tokyo: Ministry of Health and Welfare, 1996, 1997 (in Japanese). 6 Tsuji I, Nishino Y, Ohkubo T et al. A prospective cohort study on National Health Insurance beneficiaries in Ohsaki, Miyagi Prefecture, Japan: study design, profiles of the subjects and medical cost during the first year. J Epidemiol 1998;8: Tsuji I, Kuwahara A, Nishino Y et al. Medical cost for disability: a longitudinal observation of National Health Insurance beneficiaries in Japan. J Am Geriatr Soc 1999;47: Stewart AL, Hays RD, Ware JE. The MOS short-form general health survey. Med Care 1988;26: Stewart AL, Greenfield S, Hays RD et al. Functional status and wellbeing of patients with chronic conditions: results from the Medical Outcomes Study. JAMA 1989;262: SAS Institute. SAS/STAT User s Guide, Release 6.03 Edn. Cary, NC: SAS Institute Inc., Ministry of Health and Welfare, Japan. National Health Insurance Reimbursement Report (Kokumin Kenkou Hoken Iryou Kyufu Jittai Chosa Hokoku). Tokyo: Ministry of Health and Welfare, 1995 (in Japanese). 12 Ministry of Health and Welfare, Japan. National Medical Expenditures (Kokumin Iryohi). Tokyo: Ministry of Health and Welfare, 1996 (in Japanese). 13 Fries JF, Koop CE, Beadle CE et al. Reducing health care costs by reducing the need and demand for medical services. N Engl J Med 1993;329: Centers for Disease Control and Prevention. Medical care expenditures attributable to cigarette smoking United States, MMWR 1994; 43: Centers for Disease Control and Prevention. Decline in cigarette consumption following implementation of a comprehensive tobacco prevention and education program Oregon, MMWR 1999;48: Watson R. Europe agrees complete ban on tobacco advertising by BMJ 1997;315: The Smoking Cessation Clinical Practice Guideline Panel and Staff. AHCPR Smoking Cessation Guideline. JAMA 1996;275: Cromwell J, Bartosch WJ, Fiore MC, Hasselblad V, Baker T. Costeffectiveness of the clinical practice recommendations in the AHCPR guideline for smoking cessation. JAMA 1997;278: Curry SJ, Grothaus LC, McAfee T, Pabiniak C. Use and cost effectiveness of smoking-cessation services under four insurance plans in a health maintenance organization. N Engl J Med 1998;339: Smeeth L, Fowler G. Nicotine replacement therapy for a healthier nation: nicotine replacement is cost effective and should be prescribable on the NHS (editorial). BMJ 1998;317: