Body Mass Index and Disability Pension in Middle-Aged Men Non-Linear Relations

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1 Iteratioal Joural of Epidemiology O Iteratioal Epridemlotoglcal Associatio 199 Vol. 25, No. 1 Prited i Great Britai Body Mass Idex ad Disability Pesio i Middle-Aged Me No-Liear Relatios NILS-OVE MANSSON,* KARL-FREDRIK ERIKSSON,* BO ISRAELSSON,* JONAS RANSTAM,* ARNE MELANDER* AND LENNART RASTAM* Masso N-0 (Departmet of Commuity Medicie, Lud Uiversity, Uiversity Hospital MAS, Malmo, Swede), Eriksso K-F, Israelsso B, Rastam J, Melader A ad Rastam L. Body mass idex ad disability pesio i middleaged me o-liear relatios. Iteratioal Joural of Epidemiology 199; 25: Backgroud. Obesity has, i a umber of studies, bee foud to correlate to disability ad mortality, primarily due to diseases of the circulatory ad musculoskeletal systems. I additio, a excess mortality amog uderweight subjects has bee observed i previous studies. Methods. Five complete birth-year cohorts ( ) of male residets i Malmfi ( = 9) were ivited to the survey at the Departmet of Prevetive Medicie, Malmo Geeral Hospital, ad 592 (%) atteded with complete data. Each subject was followed from iclusio, defied by the date of examiatio, util the ed of the caledar year whe he tured 58, a total study period of approximately 11 years. Data o about 300 questioaire Items ad laboratory tests were determied at the health survey visit. Natiowide Swedish data registers were used for surveillace. Results. Of the participats,.% were uderweight, 3.% overweight,.3% obese ad 50.3% ormal weight; 89 (1.3%) had bee grated disability pesio at the ed of follow-up, 1 after screeig. After adjustmet for smokig there was a J-shaped relatio betwee body mass idex (BMI) ad icidece of disability pesio, the relative risk (with the ormal group as referece) amog uderweight me beig 1.9. For the overweight subjects it was 1.3 ad for the obese 2.8, all differeces were sigificat. Diseases of the musculoskeletal ad circulatory systems ad metal disorders accouted for.2% of all mai diagoses resultig i disability pesios durig follow-up. A total of 3 (.%) me died durig follow-up. Diseases of the circulatory system, eoplasms, Ijury/poisoig ad diseases of the respiratory system accouted for 91.8% of the deaths. Coclusios. Both uderweight, overweight ad obesity were related to risk of disability pesio, with a J-shaped risk relatioship. Keywords: body mass idex, disability pesio, obesity, overweight, uderweight Overweight has a egative impact o cardiovascular health, e.g. by icreasig the risk of diabetes ad hypertesio, ad reduces logevity. 1 " I additio, overweight is associated with other coditios such as osteoarthritis, ad possibly also certai cacers. I a recet Fiish study, overweight was foud to predict early retiremet but the impact o mortality was less. 8 A excess mortality amog subjects with low body mass idex (BMI) has bee observed i previous studies. 9 ' 10 It is likely that much of the health hazard associated with low weight is caused by a iverse relatioship, i.e. that the decreasig body weight is caused by a existig disease, e.g. cacer. However, Departmets of 'Commuity Medicie ad 'Medicie, Lud Uiversity, Uiversity Hospital MAS, MalmO, Swede. Reprit requests to: Dr Nils-Ove Masso, Departmet of Commuity Medicie, Lud Uiversity, Uiversity Hospital MAS, S MalmO, Swede. impaired health could also be caused by low weight or associated factors. I that case, there would be a J- or U-shaped relatioship betwee body weight ad health durig log-term follow-up. The aim of this study was, therefore, to assess the short- ad log-term relatio betwee BMI ad the risk of disability pesio. METHODS Accordig to Swedish legislatio, subjects aged 1-5 years, whose workig capacity is impaired by at least 50% (from July 1993, 25%) due to disease, ca be grated disability pesio. If the impairmet is ot regarded as permaet, temporary pesio is grated. Full disability pesio amouts to 0% of the aual icome. Much of the remaiig 0%, however, is ofte compesated for by supplemetary beefits, regulated i labour market treaties. Applicatios for disability 80

2 BODY MASS INDEX AND DISABILITY 81 pesio are dealt with by the public social isurace offices. A supportig doctor's certificate accompayig the applicatio is compulsory. Subjects The study cohort has bee preseted i detail elsewhere." I , Five complete birth-year ( ) cohorts of middle-aged male residets of Malmo, Swede ( ihabitats, 1 Jauary 19), were ivited to participate i a health screeig programme. 12 Of those ivited (9), 5932 (.1%) participated. Media age at screeig was years (95% of the subjects were, or 9 years old). This slight variatio is explaied by temporary deviatios from the origial protocol, accordig to which me bor i 192 should be icluded i 19, those bor i 192 i 195 ad so o. I the preset study, each subject was followed from iclusio, defied by the date of examiatio, util the ed of the caledar year whe he tured 58, i.e. a total study period of approximately 11 years. Screeig Methods Of the data obtaied durig the iitial health examiatio, those o body height, weight ad smokig habits were used i the preset study. Height (to the earest cm) ad weight (to the earest 0.1 kg) were measured usig calibrated scales. Body mass idex, defied as weight (kg) divided by height squared (m 2 ), was used to estimate the degree of over/uderweight ad was classified accordig to Bray ad as used o a atioal level by Statistics Swede i the Surveys of Livig Coditios. 13 ' 1 Thus, uderweight was defied as BMI <20.00, ormal weight as BMI , overweight as BMI ad obesity as BMI 3= Data o smokig habits were obtaied from a questioaire. Smokig was defied as daily smokig of cigarettes. Data o Disability Pesio Sice 191, the Natioal Social Isurace Board i Swede maitais a cumulative database of all decisios o disability pesio, permaet as well as temporary. It icludes data o year ad moth of birth, date of retiremet, type (temporary or permaet) ad extet (50, or 100% of full time) of the disability pesio, marital status ad diagoses, coded accordig to the Iteratioal Classificatio of Diseases (ICD). The 8th Revisio (ICD-8) was used util 31 December 198 ad the 9th Revisio (ICD-9) thereafter. A historic database stores data o all disability pesios valid i 191. The latter, however, is limited to type ad extet of the pesio while other data, e.g. diagoses ad time of TABLE 1 Participats i the screeig programme ( = 5932) after separatio by category of body mass idex (BMI) Category of BMI Uderweight Normal Overweight Obese (BMI missig) Rage of BMI (kg/m 2 ) <20 20-<25 25-<3O 30- No () pesio, are ot available. These two data files were used to obtai iformatio for the cohort about disability pesio before ad after the screeig. Data o Mortality I Swede, the uderlyig cause of death is registered for every subject who is residet i the coutry at the time of death. The cause is coded accordig to the ICD ad etered ito a database also cotaiig the deceased's idetificatio umber. As for data o disability pesio, ICD-8 was used util 31 December 198 ad ICD-9 thereafter. This database was used to obtai iformatio about time ad cause of death for those i the cohort who died durig follow-up. A high autopsy rate ehaces the reliability of such a database. I MalmO, the autopsy frequecy was very high from the mid 190s to the late 1980s; i 198 it was 8 ad 91% respectively for males 50-5 ad years old. Statistical Methods Proportios without pesio were aalysed usig the Kapla-Meier method ad differeces were tested with a geeralized Wilcoxo statistic. Multivariate aalyses were performed usig Cox's proportioal hazards model, i which adjusted relative risks ad their 95% cofidece itervals were calculated. A differece was cosidered statistically sigificat whe P < All tests were two-sided. RESULTS For all but six of the participats (N = 592), complete data o body height ad weight were available. Table 1 shows their distributio amog the categories of BMI. Oly half of the me had a ormal BMI. Disability Pesio A total of 89 of the me (1.3%) had bee grated a disability pesio at the ed of the year whe they tured 58. However, this proportio was ot equal

3 82 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY < Body mass idex J FIGURE 1 Rates of disability pesios durig follow-up by four categories of body mass idex amog the four categories of BMI. It was lowest amog those with ormal BMI (11.%) ad larger amog both the overweight (1.5%), the obese (2.%) ad uderweight me (.2%). Of the pesios, 132 (.5%) were grated before screeig. This proportio did ot differ sigificatly betwee the four categories of BMI. Whe oly those grated durig follow-up ( = 1) were used i the aalysis, the result was oly a mior chage i the shape of the curve which was still J-shaped (Figure 1) $ 0.85 I CO CD ~ 0.5^ 0.0 The proportio amog those with ormal weight was 9.9% ad i all other categories the proportios were sigificatly higher: uderweight 18.8% (P < ), overweight 12.% (/> = 0.01) ad obese.9% (/> < ). Figure 2 presets life-tables (Kapla-Meier) of pesio-free survival amog those who atteded the screeig without disability pesio. The two groups of uderweight ad obese me did ot differ sigificatly from each other; or did subjects with ormal weight ad overweight. Both extreme groups were sigificatly differet from those with ormal weight (P < ). Sigificat differeces were foud also betwee overweight subjects ad me who were uderweight (/> = 0.002) ad obese (P < ). After adjustmet for smokig, the relative risk (with the ormal group as referece) for acquirig a disability pesio was 1.9 (95% CI : 1.-2.) i the uderweight, 1.3 (95% CI: ) i the overweight ad 2.8 (95% CI: ) i obese me. These results persisted but were slightly weakeed after additioal adjustmet for hypertesio. Three disease categories predomiated as reasos for disability pesio (Table 2). Together, they accouted for.2% of all mai diagoses behid the disability pesios grated durig follow-up. However, the relative umber of each group of diagoses varied betwee BMI BMI BMK20.00 BMI> Follow-up (years) FIGURE 2 Pesio-free survival amog subjects who atteded the screeig without disability pesio by category of body mass idex

4 BODY MASS INDEX AND DISABILITY 83 TABLE 2 Mai diagoses servig as the foudatio for a decisio about disability pesio after separatio by category of body mass idex (BMI). Oly pesios grated after screeig were cosidered Diagosis category Category of body mass idex BMI: <20.00 Uderweight ( = 21) % 20-<25 Normal ( = 2925) % 25-<3O Overweight ( = 2190) D % 30- Obese (»18) * All ( = 59) % Diseases of the musculoskeletal system Diseases of the circulatory system Metal disorders Alcohol depedece Diabetes mellitus Other No pesio TABLE 3 Diagoses regardig musculoskeletal diseases servig as the foudatio for a decisio about disability pesio after separatio by category of body mass idex (BMI). Oly pesios grated after screeig were cosidered Diagosis category Collageoses icludig rheumatoid arthritis Arthrosis Diseases of the back Diseases of muscles ad coective tissue Other musculoskeletal diseases BMI: <20.00 Uderweight % 33 1 the differet BMI groups. For these three groups of diagoses the highest ratio of disability pesioers was foud amog subjects with obesity, ad for musculoskeletal diseases also amog those with the lowest BMI. There was a heterogeeity i this group of diagoses; arthroses were most commo amog obese me while collageoses seemed to predomiate amog those with the lowest BMI (Table 3). The highest rate of alcohol depedece as a reaso for disability pesio was foud i the group of uderweight me. Subjects who were grated disability pesio prior to screeig, i.e. i youger ages, were maily foud i the lowest BMI category. The distributios amog the differet BMI categories, from low to high, were (5.%), 55 (1.8%), (2.1%) ad (3.5%), respectively. For those who were grated disability pesio before the screeig examiatio but after 190 whe diagoses became available the predomiat diagoses were metal disorders ( = 2), diseases <25 Normal (= 101) * Category of body mass idex 25-<30 Overweight (= 118) % Obese ( = 33) * All ( = 20) % 9 13 of the musculoskeletal system (=18) ad alcohol depedece ( = 11), accoutig for 3.% of all diagoses. All of these diagoses were more commo amog subjects i the lowest BMI category. Mortality The total umber of subjects who died durig follow-up was 3 (.%). While 1 (5.9%) of those with ormal BMI ad 130 (5.8%) of those who were overweight died durig follow-up, the correspodig rates for those uderweight ad those obese were 2 (9.8%) ad 3 (9.9%), respectively. Diseases of the circulatory system, eoplasms, ijury/poisoig ad diseases of the respiratory system accouted for 91.8% of all deaths. While there was a accumulatio of deaths caused by diseases of the circulatory system i both the lowest ad highest BMI categories, eoplasms were most commo amog those with obesity ad diseases of the respiratory system i

5 8 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY the group of uderweight me. I 30 cases (2.3%) of the 110 deaths due to eoplasms the reaso was cacer i the airways or lugs. Five of these occurred amog obese me ad accouted for almost half of the mortality i eoplasms i the highest BMI category. DISCUSSION I this study BMI proved to be associated with risk of disability pesio ad also with mortality. These fidigs support the results gaied by other ivestigators, who foud that overweight icreased the risk for early retiremet. 8 The high pesio rate amog the obese me was, as expected, maily a result of a icreased morbidity i illesses that are related to obesity, e.g. diseases of the circulatory ad musculoskeletal systems. The risk of disability from metal disorders was icreased as well, a fidig cotradictory to previous results. 8 The risk of disability pesio was also higher amog me who were uderweight. This depeded primarily o two categories of disease, amely, alcohol depedece ad diseases of the musculoskeletal system. Diseases of the musculoskeletal system are a heterogeeous group i which collageoses ad diseases of muscles ad coective tissue i this study costituted the subgroup resposible for the icreased umber of disability pesios amog uderweight me (Table 3). The figures were, however, too small to make ay valid coclusios. It is well kow that death from diseases of the circulatory system is associated with overweight, but i this material uderweight subjects were also overrepreseted amog those who died from cardiovascular disease. This may be explaied by cofoudig from smokig, however, it was ot possible to draw ay coclusios i this respect sice the umber of deaths, especially i the two extreme BMI categories, was too small. Relative risks were adjusted for smokig but ot for age at etry as the me were of almost idetical age whe they participated i the screeig programme. The Cox's model would compesate for differeces i duratio of follow-up, ad, hece the age at pesioig. Although this study was based upo a relatively large material there are some circumstaces affectig the geeralizability. Accordig to the Swedish Surveys of Livig Coditios the ratio of overweight me 5-5 years old i 1988 was.%, which is slightly more tha the figure preseted i this study. It could be suspected, therefore, that if the o-participats had bee icluded the relative umber of overweight subjects would have icreased ad thus possibly iflueced the results of this study. A weakess with BMI as a idicator of overweight is also the lack of iformatio about fat distributio; the latter is cosidered to be a better risk idicator for disease, especially diseases of the circulatory system. 1 Aother problem is the effects of early selective mortality which, of course, could ot be accouted for i the curret study. Daily smokig of cigarettes may be too rough a measure sice the umeasurable aspects of smokig, such as depth of ihalatio, ca affect the outcomes. The results may also have bee iflueced by other cofouders, of which oly smokig was cosidered i this material. I additio it seems that the associatio betwee weight ad disability pesio was iflueced by the age at which a pesio was grated. This supports the fidigs i a previous study i which obesity was foud to correlate with morbidity ad mortality i log-term but ot i short-term prospective aalyses. 1 The cessatio of follow-up at age 58 was motivated by the fact that, i those aged 59-0 years ad older, other optios for retiremet (volutary with o demads for disability) are available i Swede. It is likely, therefore, that at those ages, retiremets due to disability were ot registered as such. I this study BMI was aalysed i relatio to disability pesio; ot morbidity per se. The diagosis reported as the foudatio for the decisio about disability pesio may ot be the oly, or eve the accurate, reaso for the early retiremet. Socioecoomic factors, such as legislative cosideratios, level of educatio, uemploymet, marital status ad type of commuity, may have played a role i the process leadig to disability pesio. 18 However, it seems clear that both uder- ad overweight, especially obesity, were associated with disability pesio ad, to a lesser degree, with mortality. Diseases of the musculoskeletal ad circulatory systems accouted for disability amog both uderweight ad obese subjects. However, the excess umber of thi me grated disability pesio was small ad the risk of beig uderweight might have bee overestimated due to bias discussed above. Thus, accordig to the fidigs i this study, obesity i particular remais a risk factor for disability ad mortality. Severe overweight also affects risk of morbidity i a wider cotext, quality of life ad for society, icreased costs for health care ad loss of productivity. Thus, prevetig overweight is a importat task with a umber of positive effects, e.g. a probable reductio of disability. ACKNOWLEDGEMENTS This study was supported by grats from The Medical Faculty Lud Uiversity, Malmo City Coucil, the

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