International Journal of Obesity (1998) 22, 949±957 ß 1998 Stockton Press All rights reserved 0307±0565/98 $12.00 http://www.stockton-press.co.uk/ijo Predictors of major weight gain in adult Finns: Stress, life satisfaction and personality traits

M Korkeila1, J Kaprio1,2, A Rissanen3, M Koskenvuo4 and TIA SoÈrensen5

1Department of Public Health, University of Helsinki, Helsinki; 2Department of Mental Health and Alcohol Research, National Public Health Institute, Helsinki; 3Department of Psychiatry, Helsinki Central University Hospital, Helsinki; 4Department of Public Health, University of Turku, Turku, Finland; and 5Danish Epidemiology Science Centre at the Institute of Preventive Medicine, Copenhagen University Hospital, Copenhagen, Denmark

OBJECTIVE: To study how stress, life satisfaction and personality related factors, are related to long-term major weight gain. DESIGN: Prospective cohort study, with follow-up by questionnaire at 6 y and 15 y with a within-study replication. SUBJECTS: 5867 twin pairs aged 18±54 y at baseline, considered as two sets of unrelated individuals in analyses. MAIN OUTCOME MEASURES: Adjusted odds ratios (OR) for 10 kg weight gain over 6 y and 15 y. RESULTS: A high level of stress at baseline, was a predictor for major weight gain over 6 y, and this effect was consistent in some groups even over 15 y. Low levels of life satisfaction and high scores for neuroticism, were predictors for weight gain in older women. These effects were consistent, even after adjustments for confounding variables (education, dieting, smoking, alcohol consumption and pregnancy in women). High levels of extroversion showed a trend towards lesser weight gain in younger men. CONCLUSION: Psychological traits did not affect the risk of major long-term weight gain in a uniform fashion. The observed effects of the factors related to psychological health were modest and consistent, but varied by age and gender. Thus, there may be trait-speci®c effects in selected subgroups of the population that should be further investigated.

Keywords: weight change; stress; life satisfaction; extroversion; neuroticism

Introduction scale, and it is not easy to incorporate reliable measures of personality into such studies. Thus, to our knowledge there have been no earlier prospective Personality characteristics or pro®les, speci®c to studies of personality factors or experienced stress as obesity, have not been found,1,2 although group dif- predictors of weight gain. ferences between obese and normal weight subjects We studied baseline measures on stress, life satis- on some dimensions, have been identi®ed in selected faction, extroversion and neuroticism, in relation to studies. Cross-sectional data show that depressive weight gain, over 6 y and 15 y, respectively. The study symptoms, psychological distress and low levels of population is a twin cohort, from which we included life satisfaction, are more common among obese than one member of each twin pair, selected at random, for normal weight subjects.3±6 Stress, induced by nega- the initial analysis. Then, a set of con®rmatory ana- tive life events, and depressive symptoms, have been lyses were carried out on the subjects not included in identi®ed as risk factors for short- and long-term the initial analyses, to assess the consistency of the weight gain in prospective studies.7,8 Obese subjects results, as has been done in the previous studies from have been reported to be more extrovert than their the Finnish Twin Cohort.11 The aim of the present normal weight controls, whereas no differences have study was to examine whether personality related been found in the levels of neuroticism.9,10 In cross- factors are predictors for long-term major weight sectional studies, the resolution of causality is not gain in Finnish adults. possible, and thus the observed differences in psycho- logical characteristics, between obese and non-obese subjects, may be as much cause as effect. There have been very few prospective studies of psychosocial Subjects and methods factors as predictors of weight gain and obesity. Such prospective studies are necessarily of a large The Finnish Twin Cohort This study is based on data from the older part of the Finnish Twin Cohort compiled in 1974. The Cohort Correspondence: M Korkeila, Department of Public Health, includes 13 888 monozygotic and same-gender di- PO Box 41, 00014 University of Helsinki, Finland. Received 1 December 1997; revised 22 April 1998; accepted zygotic twin pairs, born before 1958 with both mem- 12 12 May 1998 bers alive in 1967. Twin individuals received a Predictors of major weight gain M Korkeila et al 950 questionnaire in 1975 and the response rate was 89%. metropolitan area of Helsinki in 1994±1995.15 The questionnaire had items on health, weight, height, There were 100 men (mean age 52.5 y, s.d. 6.5) and life-style and psychosocial factors, including person- 125 women (mean age 50.4 y, s.d. 7.9) with self- ality and stress. A second questionnaire was mailed in reported height and weight from the 1990 question- 1981 to the living twin individuals in the cohort, with naire, and whose height and weight were measured as an overall response rate of 84%. A third questionnaire a part of a clinical examination. BMI values were was mailed in 1990 to those twins born between computed from the self-reported and measured values, 1930±1957, with both twins in a pair known to be and these were in agreement. The regression equations alive (n ˆ 17 876 individuals, 8938 pairs). The were: for men, BMImeasured ˆ 3.4 ‡ 0.90 BMI1990 response rate to the 1990 questionnaire was 77%. (standard error for regression coef®cient ˆ 0.047) Both of the follow-up questionnaires included items and for women, BMImeasured ˆ 0.9 ‡ 1.02 BMI1990 on current weight and height used in the present (s.e. 0.04), and the correlations were correspondingly analyses. 0.89 and 0.90.

The study population Predictive variables and co-variables The present study is based on two follow-up periods extending to 6 y (1975±1981) and 15 y (1975±1990), Stress. Stress of daily activities, was de®ned by four respectively. Two groups were formed by selecting at self-reported items, asking the respondent to assess random one co-twin from each pair, to form two how well the following statements ®t them: samples of unrelated individuals. These were termed 1. In general, I am unusually tense and nervous. Twin A and Twin B samples, but were also random 2. There is a great deal of stress connected with my with respect to birth order. The pairs of twins were daily activities. aged 18±54 y in 1975 and provided complete data on 3. At the end of day, I am mentally and physically weight from the surveys in 1975 and 1981, and with completely exhausted. data on height from at least one of the surveys. For the 4. My daily activities are extremely trying and stress- analyses of weight changes over 6 y, each group had ful. 3536 men and 4193 women at baseline. For the analyses on the 15 y follow-up, we included subjects The response alternatives (very well, well, poorly, who had also responded to the last questionnaire very poorly) were scored 1±4, with sum score ranging (2152 men and 2721 women). All the analyses were from 4±16. Correlation coef®cients of scale items and made of both men and women in two age groups (18± total score distributions, have been described else- 29 y and 30±54 y at baseline) separately, because where.16 Cronbach's alpha, which is a measure of test patterns of weight gain differed by gender and age.13 reliability, was 0.80 for males and 0.81 for females. Women with pregnancies were excluded from some This scale was then divided into three groups with analyses (n ˆ 1195 for the 6 y follow-up and n ˆ 1191 high levels of stress (4±8 points), some stress (9±15 for the 15 y follow-up). In brief, data from the national points) and little stress (16 points), experienced hospital discharge registry on deliveries, were used to daily.17 identify women pregnant at the time of the question- naire studies, or in the period between them, using the time-related criteria given in detail elsewhere.14 Life satisfaction. Life satisfaction was measured Women who had been pregnant between the last two according to Allardt's four item scale (1973) on surveys (1981±1990) were identi®ed by a question on levels of interest, happiness, easiness and loneliness 16 family structure in the 1990 questionnaire and hospital of life, as described previously in detail. Cronbach's data. The remaining number of women included in the alpha was 0.74 for both men and women. The scale analyses for the Twin A sample was 2998 for the was then divided into groups with high (0±7), mod- shorter (6 y) and 1530 for the longer (15 y) follow-up. erate (8±10) and low (11±15) levels of life satisfac- tion. A detailed presentation on the scales, correlation coef®cients of scale items and total score distribu- Determination of weight change tions, have been described in detail earlier.16,18 Weight change (Dwt) was determined as the differ- ence between the self-reported weights given in 1975 and 1981, and in 1975 and 1990. In the questionnaires, Extroversion and neuroticism. Extroversion and weight was given in kg and height in cm, which, when neuroticism were measured using the abbreviated necessary, were rounded to the nearest integral Eysenck Personality Inventory (EPI)19 including ten number. Body mass index (BMI) (weight (kg)=height items for the assessment of neuroticism and nine items (m) squared) was used as a measure of fatness. A gain for extroversion.20,21 The ten-item scale for neuroti- of > 10 kg was regarded as a major weight gain and cism was analysed in three groups (0±2 points for was the outcome measure in analyses. low, 3±6 points for medium and 7±10 points for high The validity of self-reported weights in 1990, was levels of neuroticism). The nine-point extroversion ascertained in a sample of twins living in the scale was also trichotomized to yield high (7±9 Predictors of major weight gain M Korkeila et al 951 points), moderate (3±6) and low (0±2) levels of variable across categories. The categories of the study extroversion. variable were assigned scores from unity onwards In addition to baseline age and BMI, the following (1, 2, 3). The signi®cance of the trend was assessed baseline (1975) variables were included as covariates from the regression coef®cient of the scored variable in the multivariate analysis. relative to its standard error. The multivariate analyses were then repeated on the Twin B sample. We also undertook power analysis (EGRET.SIZ, Dieting at baseline. The subjects were asked Epidemiological Graphics, Estimation, and Testing whether they were attempting to lose weight because package, 1992±1993, Statistics & Epidemiological of obesity. Research Corporation, Seattle, USA) to assess whether there was a theoretical possibility of detecting Smoking. Based on a detailed smoking history, the personality-related effects, given the size of our respondents were classi®ed as non-smokers or occa- sample. Thus, the power analysis aims to relate a sional, previous or current cigarette smokers.22 Smok- chosen level of power directly to an OR value. The ing quantity was based on the number of cigarettes program requires sample distributions (n, %) of all smoked daily and categorized for current smokers as covariates (for example, age, BMI at baseline, stress), 1±14 or  15 cigarettes=d. the proportions of subjects with the outcome in the sample, and univariate outcome OR values, whereas power and an alpha-level can be chosen freely by the Use of alcohol. The frequency, quantity and type of investigator. As an example, a power analysis for alcohol used, were rated by the responses to six stress (three categories) using the distributions by questions on current use of alcoholic beverages and gender (men, women), baseline age (®ve-year age converted into grams of ethanol, to give the monthly groups) and BMI (< 22, 22±24.99, 25±26.99, 27± 23 consumption of pure alcohol. The subjects were 29.99,  30) indicated that the study had 80% power classi®ed into abstainers (no use), occasional users at an alpha-level of 0.05 to detect an OR of 1.3 (1±150 g=month), moderate users (151±399 g/month) between the highest and lowest categories of stress. and heavy users (  400 g=month). For an OR ˆ 1.2, the power was 48%, while for an OR ˆ 1.4 the power was 94%. Educational level. This was classi®ed into three classes: primary (lowest level), secondary (middle level) and tertiary (highest level) education. Results Statistical methods Statistical analyses were made using the BMDP soft- The baseline characteristics of the sample are shown ware program. Analysis of covariance (ANCOVA) in Table 1. Weight gain was most common in young was used to test the hypothesis that means of BMI, by and initially lean subjects and more common in males categories of psychological variables, were equal than females. The ORs for major weight gain were while adjusted for age. therefore adjusted for the initial BMI, and strati®ed by Odds ratios (OR) for gaining > 10 kg in the male gender and age group. and non-pregnant female Twin A sample, were The means of BMI for the study subjects, in relation assessed by logistic regression analysis.24 Weight to the levels of stress, life satisfaction, extroversion changes were adjusted for age and BMI at baseline and neuroticism, are presented in Table 2. Few sig- and the OR were computed over the two follow-up ni®cant associations emerged in the cross-sectional periods (6 y and 15 y) within age groups 18±29 y and analysis. Older men with much stress and older 30±54 y. Signi®cance was estimated by the 95% women with high scores for neuroticism, had higher con®dence intervals (CI). BMI (ANCOVA P < 0.05) at baseline than other To test the independence of effects of personality subjects in the respective groups. related factors, on weight change over 6 y and 15 y, In the univariate analyses (Figure 1 and Figure 2), further logistic regression analyses were carried out on elevated levels of stress at baseline predicted major the Twin A sample. In addition to initial age and BMI, weight gain in men over 6 y. This effect was not seen four additional terms (education, dieting, alcohol over 15 y. A low level of life satisfaction predicted consumption and smoking at baseline Ð results to be major weight gain in older women over 6 y. No clear reported elsewhere) were included in the logistic trends emerged for men or younger women over the regression equation, to obtain covariate-adjusted risk follow-up. There was a decreased risk for weight gain estimates. Pregnancy during or in between the in younger men with high scores of extroversion. questionnaires, was included as a covariate in the Extroversion did not predict major weight gain in model among women. A trend test was performed in women. High levels of neuroticism were related to conjunction with the multivariate approach, to assess risk for major gain over 6 y in women only. Neuroti- whether there was a signi®cant trend in the ORs for the cism was not related to risk for gaining weight in men. Predictors of major weight gain M Korkeila et al 952 Table 1 Body mass index (BMI) at baseline (x, s.d.), weight changes (kg) (x, s.d.), and the proportion gaining > 10 kg (%) in 6 y and 15 y. Twin A sample, The Finnish Twin Cohort, 1975, 1981 and 1990 questionnaire studies.

BMI at baseline Weight change (kg) Proportion gaining >10 kg n

(x , s.d.) 6 y (x , s.d.) 15 y (x , s.d,) 6 y (%) 15 y (%) 6 y (n) 15 y (n)

Men Age 18±29 y 22.36 (2.50) 3.60 (5.54) 7.57 (7.70) 8.8 29.8 1877 1220 Age 30±54 y 24.86 (2.81) 1.36 (4.51) 3.50 (6.22) 3.2 11.3 1659 932 Women Age 18±29 y 20.84 (2.58) 1.95 (4.57) 5.90 (8.13) 3.5 19.4 1268 589 Age 30±54 y 23.65 (3.37) 1.59 (4.30) 5.54 (7.88) 2.6 15.9 1730 941

A total of n ˆ 1195 and nˆ 1191 women excluded due to pregnancy for the 6 y and 15 y follow-ups, respectively (see Methods).

Table 2 Mean body mass index (BMI) at baseline by levels of stress, life satisfaction, extro-version, neuroticism by gender and age group. Twin A sample, The Finnish Twin Cohort 1975 questionnaire study

Men Women

18^29 y 30^54 y 18^29 y 30^54 y

Stress No 22.43 (0.13) 25.09 (0.17) 20.75 (0.15) 23.70 (0.17) Some 22.33 (0.06) 24.69 (0.08) 20.74 (0.08) 23.45 (0.10) Much 22.43 (0.24) 25.32 (0.26) 20.72 (0.26) 23.60 (0.26) P ˆ 0.74 Pˆ 0.01 P ˆ 0.99 P ˆ 0.44 Life satisfaction High 22.44 (0.08) 24.86 (0.10) 20.76 (0.10) 23.53 (0.11) Moderate 22.32 (0.09) 24.82 (0.11) 20.70 (0.12) 23.84 (0.13) Low 22.21 (0.13) 24.94 (0.19) 20.81 (0.16) 23.58 (0.19) Pˆ 0.28 P ˆ 0.86 P ˆ 0.85 P ˆ 0.18 Extroversion Low 22.12 (0.11) 24.75 (0.13) 20.59 (0.12) 23.54 (0.13) Medium 22.34 (0.08) 24.87 (0.10) 20.85 (0.10) 23.75 (0.11) High 22.61 (0.11) 25.00 (0.15) 20.77 (0.15) 23.55 (0.19) P ˆ 0.51 P ˆ 0.45 P ˆ 0.27 P ˆ 0.37 Neuroticism Low 22.38 (0.10) 24.73 (0.12) 20.91 (0.17) 23.39 (0.15) Medium 22.35 (0.08) 24.85 (0.10) 20.66 (0.09) 23.58 (0.10) High 22.33 (0.13) 25.06 (0.16) 20.79 (0.13) 24.10 (0.19) Pˆ 0.95 Pˆ 0.25 P ˆ 0.39 P  0.001

P ˆP-value from F-test for equality of means by ANCOVA. A total of nˆ 1195 and n ˆ 1191 women excluded due to pregnancy for the 6 y and 15 y follow-ups, respectively (see Methods).

The ORs for weight gain > 10 kg over 6 y and 15 y 0.86±2.66 for women), but were so at 15 y in relation to baseline variables, after adjustment for (OR ˆ 2.77, 1.06±7.26 for men and OR ˆ 1.40, education, dieting, alcohol consumption, smoking at 1.02±1.93 for women), but these were not found baseline and pregnancy in women, are shown in Table upon replication. Two signi®cant results (high levels 3. High levels of stress in young males (OR ˆ 2.72, of neuroticism over 6 y and low levels of life satisfac- 95% CI 1.29±5.73, P for trend ˆ 0.007), low life tion over 15 y in women) were found in the replication satisfaction (OR ˆ 2.21, 95% CI 1.05±4.64, not found in the original analysis. P ˆ 0.043) and high neuroticism (OR ˆ 4.29, 95% CI 1.70±10.8, P < 0.001) in older women, remained signi®cant predictors for major weight gain after Discussion adjustment for covariates in the multivariate analysis. These trends were replicated in the Twin B sample, yet the trend was signi®cant only for neuroticism in The aim of this study was to examine whether older women. Young men with high levels of extro- personality related variables predict major weight version, showed a trend towards less weight gain gain over two relatively long follow-up periods (6 y (OR ˆ 0.65, 95% CI 0.41±1.04, P for trend 0.080), and 15 y). Earlier prospective studies are few and which was found for the second twin on replication. focus on short-term weight changes during, at max- The ORs were elevated for moderate to high levels of imum, one year. These studies show that current stress, which were not signi®cant at 6 y (OR ˆ 2.25, depression and recent negative life events are con- 95% CI 0.55±9.31 for men and OR ˆ 1.51, 95% CI nected to subsequent weight changes.7,8 To our Predictors of major weight gain M Korkeila et al 953

Figure 1 Factors related to personality: stress and life satisfaction. Odds ratios (OR) adjusted for age and body mass index (BMI) at baseline for > 10 kg weight gain over 6 y and 15 y follow-up in men and non-pregnant women by age-group. Twin A sample, Finnish Twin Cohort, 1975, 1981 and 1990 questionnaire studies.

Figure 2 Factors related to personality: extroversion, neuroticism. Odds ratios (OR) adjusted for age and body mass index (BMI) at baseline for > 10 kg weight gain over 6 y and 15 y follow-up in men and non-pregnant women by age-group. Twin A sample, Finnish Twin Cohort, 1975, 1981 and 1990 questionnaire studies. knowledge, there are no earlier prospective data on extroversion were related to decreased risk of major long-term effects of the factors studied in the present weight gain in young men. These observed ®ndings study. mostly weakened over the longer follow-up. A few signi®cant ®ndings emerged in the present We speculate that an increased fat or energy intake study. The main observations are that a high level of may be a response to stress and may lead to long-term stress at baseline predicts major weight gain over 6 y weight gain. No uniform pattern of how stress affects in men; a low level of life satisfaction and high score food intake has been found in earlier literature.25,26 of neuroticism also tended to be risk factors for major The long-term effects of stress may vary within the gain over 6 y in older women; high levels of population, as the connection between stress and Predictors of major weight gain M Korkeila et al 954 Table 3 Multivariate analysis of weight changes on factors related to personality: stress, life satisfaction, extroversion and neuro- ticism. Subjects (n) and odds ratios (OR) for > 10 kg weight gain over two follow-up periods (6 y and 15 y) adjusted for age, body mass index (BMI), education, dieting, alcohol consumption, smoking at baseline and pregnancy in women. Comparison of twin individuals by random assignment (Twin A, Twin B). The Finnish Twin Cohort 1975, 1981 and 1990 questionnaire studies. Numbers (n) for the Twin B sample differ slightly due to missing values in study variables.

Twin A Twin B

At 6y (n) At15y (n) OR (CI) 6y OR (CI) 15y OR (CI) 6y OR (CI) 15y

Stress Men 18±29 y No 333 216 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Some 1324 869 1.65 (1.01±2.71) 1.10 (0.79±1.54) 1.37 (0.89±2.11) 1.03 (0.74±1.44) Much 92 58 2.72 (1.29±5.73) 1.06 (0.56±2.03) 1.38 (0.60±3.19) 0.75 (0.36±1.58) P for trend 0.007 0.667 0.190 0.746 Men 30±54 y No 256 147 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Some 1099 646 2.24 (0.78±6.44) 2.04 (0.98±4.24) 0.74 (0.30±1.85) 0.92 (0.49±1.72) Much 111 71 2.25 (0.55±9.31) 2.77 (1.06±7.26) 1.36 (0.41±4.55) 1.32 (0.53±3.24) P for trend 0.190 0.029 0.780 0.672 Women 18±29 y No 459 342 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Some 1552 1090 1.51 (0.86±2.66) 1.40 (1.02±1.93) 0.96 (0.55±1.68) 0.85 (0.63±1.16) Much 142 96 0.83 (0.26±2.57) 1.13 (0.63±2.04) 1.74 (0.78±3.88) 1.16 (0.68±1.99) P for trend 0.582 0.165 0.322 0.889 Women 30±54 y No 344 190 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Some 1112 690 1.70 (0.69±4.19) 1.07 (0.67±1.70) 1.19 (0.57±2.49) 1.18 (0.76±1.82) Much 151 89 2.35 (0.72±7.66) 1.35 (0.68±2.66) 1.94 (0.71±5.33) 1.21 (0.62±2.35) P for trend 0.139 0.440 0.234 0.490 Life satisfaction Men 18±29 y High 877 582 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Moderate 656 432 1.16 (0.80±1.66) 1.05 (0.80±1.38) 0.88 (0.61±1.27) 1.04 (0.78±1.39) Low 311 185 0.98 (0.61±1.59) 0.95 (0.65±1.38) 1.14 (0.74±1.76) 0.86 (0.59±1.26) P for trend 0.852 0.903 0.738 0.567 Men 30±54 y High 790 484 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Moderate 618 350 0.78 (0.41±1.48) 1.26 (0.81±1.98) 0.83 (0.36±1.92) 1.32 (0.83±2.09) Low 224 90 1.36 (0.64±2.88) 1.61 (0.84±3.10) 2.40 (1.07±5.37) 0.99 (0.49±2.00) P for trend 0.659 0.124 0.078 0.621 Women 18±29 y High 1162 843 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Moderate 757 526 1.11 (0.72±1.74) 1.0 (0.77±1.31) 1.26 (0.80±2.01) 1.20 (0.92±1.58) Low 339 232 1.11 (0.62±1.98) 1.28 (0.91±1.80) 1.53 (0.86±2.73) 1.65 (1.16±2.35) P for trend 0.638 0.246 0.126 0.005 Women 30±54 y High 948 586 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Moderate 625 353 1.29 (0.66±2.54) 1.17 (0.81±1.69) 2.00 (1.13±3.56) 0.98 (0.68±1.40) Low 289 139 2.21 (1.05±4.64) 1.00 (0.59±1.70) 1.25 (0.56±2.79) 1.15 (0.73±1.82) P for trend 0.043 0.729 0.230 0.636 Extroversion Men 18±29 y Low 423 284 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Medium 957 618 0.66 (0.44±0.99) 0.96 (0.70±1.32) 0.78 (0.53±1.17) 1.09 (0.78±1.53) High 463 297 0.65 (0.41±1.04) 1.06 (0.74±1.53) 0.64 (0.40±1.02) 1.12 (0.77±1.65) P for trend 0.080 0.728 0.059 0.555 Men 30±54 y Low 465 268 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Medium 821 451 1.61 (0.78±3.35) 1.88 (1.10±3.21) 0.59 (0.27±1.26) 0.84 (0.50±1.43) High 347 205 1.39 (0.58±3.36) 1.01 (0.51±2.00) 0.80 (0.32±1.97) 1.11 (0.56±2.02) P for trend 0.443 0.876 0.509 0.724 Women 18±29 y Low 683 494 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Medium 1082 775 0.75 (0.47±1.19) 0.72 (0.55±0.95) 1.45 (0.86±2.44) 1.37 (1.02±1.85) High 491 332 0.96 (0.56±1.65) 0.88 (0.63±1.23) 1.44 (0.77±2.67) 1.37 (0.95±1.97) P for trend 0.772 0.303 0.234 0.070 Women 30±54 y Low 636 376 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Medium 907 517 1.05 (0.56±1.98) 1.21 (0.83±1.76) 0.81 (0.46±1.43) 0.80 (0.56±1.15) High 323 185 0.93 (0.39±2.21) 0.95 (0.57±1.59) 0.74 (0.35±1.61) 1.01 (0.65±1.58) P for trend 0.919 0.927 0.395 0.846 Neuroticism Men 18±29 y Low 582 378 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Medium 917 612 1.14 (0.77±1.69) 0.89 (0.67±1.18) 1.37 (0.94±2.01) 1.13 (0.84±1.53) High 344 210 1.42 (0.88±2.28) 0.98 (0.68±1.43) 0.96 (0.57±1.61) 0.98 (0.66±1.47) P for trend 0.159 0.793 0.827 0.926

continued Predictors of major weight gain M Korkeila et al 955 Table 3 continued.

Twin A Twin B

At 6y (n) At15y (n) OR (CI) 6y OR (CI) 15y OR (CI) 6y OR (CI) 15y

Men 30±54 y Low 512 299 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Medium 818 461 1.24 (0.63±2.44) 1.25 (0.76±2.04) 0.96 (0.42±2.18) 0.96 (0.59±1.57) High 299 166 0.90 (0.37±2.19) 1.12 (0.59±2.10) 1.75 (0.71±4.28) 1.02 (0.54±1.90) P for trend 0.894 0.972 0.242 0.991 Women 18±29 y High 397 292 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Medium 1211 850 0.82 (0.48±1.39) 1.01 (0.72±1.41) 0.83 (0.45±1.51) 0.75 (0.55±1.03) High 646 457 0.75 (0.41±1.37) 1.10 (0.76±1.59) 1.62 (0.87±3.01) 0.84 (0.59±1.21) P for trend 0.368 0.585 0.038 0.464 Women 30±54 y Low 459 259 1.0 (±) 1.0 (±) 1.0 (±) 1.0 (±) Medium 997 590 1.48 (0.59±3.75) 0.94 (0.61±1.43) 1.03 (0.50±2.13) 0.88 (0.59±1.32) High 405 227 4.29 (1.70±10.8) 1.25 (0.77±2.04) 2.05 (0.96±4.35) 1.12 (0.71±1.78) P for trend < 0.001 0.360 0.038 0.603

OR ˆ odds ratios; CI ˆ 95% con®dence intervals. eating has been shown to be modi®ed by dietary Women who were pregnant at the time of each restraint.27 Schachter et al28 stimulus response questionnaire or in between, they corresponded close theory suggests that the response to stress may differ to one third (28.5%) of the initial female sample. The according to initial weight status and there are studies baseline BMI among pregnant vs non-pregnant demonstrating that stress leads to overeating only in women did not differ, but the 15 y weight gains subgroups of initially obese subjects.8,29,30 Psycho- were higher if pregnant women were included. We social stress has been shown to favour central obe- excluded pregnant women from the logistic regression sity.31 The observed association between stress and analyses, where psychological factors were adjusted weight gain might therefore have been stronger, if the for age and initial weight only. In the multivariate localisation of fat could have been taken into account. analyses of the confounding factors, pregnancy was Fluctuating weight has been shown to relate to lower included as a covariate in the model. Pregnancy had levels of well-being, especially in women, so recent no substantial confounding effect, as the exclusion of weight changes may even increase stress.32,33 pregnant women from the multivariate analyses did The signi®cant effects of predictors for major gain not change the results substantially. tended to disappear during the longer follow-up. The We wanted to include variables measured with effects of the study variables may not extend over the validated scales representing both stable and circum- longer follow-up, or this inconsistency may be due to stantial characteristics of personality in the analyses. the fact that the 15 y sample was a subsample of the Extroversion and neuroticism are regarded as stable 6 y sample. The developmental state of weight history characters of personality and are central dimensions of during adulthood might be one additional explanatory personality theory.21,37 Stress and life satisfaction are factor, as well as the fact that predisposition to gain considered more circumstantial and therefore labile, weight is reported to vary on the lifespan.34,35 but they also had adequate psychometric proper- In the present study, twinship was ignored and the ties.16; 17 Stress has face validity as a measure of the analyses carried out as two sets of unrelated indivi- degree to which current activities are considered duals to examine whether psychological measures stressful by the respondent and predicts the onset of consistently predict weight gain in a prospective peptic ulcers.17 The life satisfaction scale is an index setting. We repeated the multivariate analyses using of global happiness with the current life situation. data of the other twin and the results showed weaker, Poor life satisfaction predicts suicidal behavior and but consistent relationships as similar trends were incidence of mental illness.18 seen in both samples. The weaker effect observed in A 10 kg cutpoint, corresponding to an approximate some of the con®rmatory analyses, may result from increase of three units of BMI, was used as the sample variation, because the power analysis indi- threshold value of major weight gain in the present cated suf®cient sample size to detect even quite study. Unfortunately, any arbitrary cutpoint leads to modest effects. loss of information. However, a high cutpoint is If psychological traits with major effect on weight unlikely to re¯ect random variation and small gain had been detected, a next stage would have been weight ¯uctuations, and it may be less sensitive to to examine whether these are independent of genetic query bias. A high cutpoint might also be less sensi- effects on weight gain using the twin design.36 How- tive to unavoidable misreporting when using self- ever, strong associations between the psychological reported weight data.38±42 measures and weight gain were not detected, and We adjusted the studied variables for initial age and therefore the twin analyses were not carried out. BMI. It is possible that the distribution and effects of Predictors of major weight gain M Korkeila et al 956 personality-related factors are dependent on the 8 Van Strien T, Rookus MA, Bergers GPA, Frijters JER, weight status of the subjects. These interactions, Defares PB. Life events, emotional eating and change in body mass index. Int J Obes 1986; 10: 29±35. however, were not the focus of the study. In a multi- 9 HaÈllstroÈm T, Noppa H. Obesity in women in relation to mental variate approach, after the adjustment for signi®cant illness, social factors and personality traits. J Psychosom Res additional environmental factors, the effects of stress, 1981; 25: 75±82. life satisfaction and neuroticism, remained as inde- 10 Kittel F, Rustin RM, Dramaix M, de Backer G, Kornitzer M. pendent predictors in some subgroups. The multi- Psycho-sociobiological correlates of moderate overweight in an industrial population. J Psychosom Res 1978; 22: variate approach may mask important relationships, 145±158. if the covariates are mediating the effect of person- 11 Aarnio M, Kujala UM, Kaprio J. Associations of health- ality on weight gain.43 For example, psychological related behaviors, school type and health status to physical health is shown to be dependent on socioeconomic activity patterns in 16 year old boys and girls. Scand J Soc status, as well as educational achievement is shown to Med 1997; 25: 156±167. 12 Kaprio J, Sarna S, Koskenvuo M, Rantasalo I. The Finnish modify the effects of personality and weight gain in a Twin Registry: Formation and compilation, questionnaire 7; 44 longitudinal setting. The multivariate results study, zygosity determination procedures and research should thus be regarded as a con®rmation of the program. Prog Clin Biol Res 1978; 24b: 179±184. univariate analyses and the results should not be 13 Korkeila M, Kaprio J, Rissanen A, Koskenvuo M. Weight interpreted separately from the original context. changes among 13 097 adult Finns over six years. In: Ail- haud G, Guy-Grand B, Lafontan M, Ricquier D (eds) Obesity in Europe 91. John Libbey: London, 1991, pp 129±133. Conclusion 14 Korkeila M, Kaprio J, Rissanen A, Koskenvuo M. Effects of gender and age on the heritability of body mass index. Int J Obes 1991; 15: 647±654. Circumstantial factors related to psychological health 15 Harrela M, Koistinen H, Kaprio J, Lehtovirta M, Tuomilehto at baseline, predict major weight gain over 6 y in some J, Eriksson J, Toivanen L, Koskenvuo M, Leinonen P, groups. High neuroticism scores in older women, and Koistinen R, SeppaÈlaÈ M. Genetic and environmental compo- nents of interindividual variation in circulating levels of IGF- low levels of extroversion in young men were stable 1, IGF-II, IGFBP-1, and IGFBP-3. J Clin Invest 1996; 98: personality characters related to subsequent weight 2612±2615. gain. However, the observed effects were fairly 16 Koskenvuo M, Langinvainio H, Kaprio J, Rantasalo I, Sarna S. modest and extended over 6 y but not over 15 y of The Finnish Twin Registry: Baseline characteristics. Section follow-up. Further studies on the long-term effects III. Occupational and psychosocial factors. Kansanterveystie- teen julkaisuja M 49 (Publications in Public Health), 1979, of chronic stress on weight changes in adults are Helsinki Univ. Press, Helsinki. warranted. 17 RaÈihaÈ I, Kemppainen H, Kaprio J, Koskenvuo M, Sourander L. Life-style, stress and genes in peptic ulcer disease. A nationwide twin cohort study. Arch Int Med 1998; 158: Acknowledgements 698±704. Supported by the Academy of Finland. MK is sup- 18 Koivumaa-Honkanen HT. Life satisfaction as a health ported by the Doctoral Programs in Public Health, predictor. Academic dissertation. Kuopio University Publica- University of Helsinki. We thank Olli Lounela, sys- tions D. Medical sciences 1998, 143, pp 80±83. 19 Floderus B. Psycho-social factors in relation to coronary heart tems analyst, for producing the ®gures and Kauko disease and associated risk factors. Nord Hyg Tidskr Suppl 6, HeikkilaÈ, systems analyst, for database management. 1974. 20 Rose RJ, Koskenvuo M, Kaprio J, Sarna S, Langinvainio H. Shared genes, shared experiences, and similarity of personal- References ity: Data from 14 288 adult Finnish co-twins. J Pers Soc 1 Larsen F, Torgersen S. Personality changes after gastric Psychol 1988; 54: 161±171. banding surgery for morbid obesity. A Prospective study. 21 Viken RJ, Rose RJ, Kaprio J, Koskenvuo M. A developmental J Psychosom Res 1989; 33: 323±334. genetic analysis of adult personality: Extroversion and neuro- 2 Leon G, Roth L. Obesity: Psychological causes, correlations, ticism from 18 to 59 years of age. J Personality and Soc and speculations. Psychol Bull 1977; 84: 117±139. Psychol 1994; 66: 722±730. 3 Moore ME, Stunkard AJ, Srole L. Obesity, social class, and 22 Kaprio J, Koskenvuo M. A prospective study of psychological mental illness. JAMA 1962; 15: 962±966. and socioeconomic characteristics, health behavior and mor- 4 Sullivan M, Karlsson J, SjoÈstroÈm L, Backman L, Bengtsson C, bidity in cigarette smokers prior to quitting compared to Bouchard C, Dahlgren S, Jonsson E, Larsson B, Lindstedt S, persistent smokers and non-smokers. J Clin Epidemiol 1988; NaÈslund I, Olbe L, Wedel H. Swedish obese subjects (SOS) ± 41: 139±150. an intervention study of obesity. Baseline evaluation of health 23 Romanov K, Rose RJ, Kaprio J, Koskenvuo M, Langin- and psychosocial functioning in the ®rst 1743 subjects exam- vainio H, Sarna S. Self-reported alcohol use: a longitu- ined. Int J Obes 1993; 17: 503±512. dinal study of 12 954 adults. In: Lindros KO, Ylikahri R, 5 Istvan J, Zavela K, Weidner G. Body weight and psycho- Kiianmaa K (eds). Advances in Biomedical Alcohol logical distress in NHANES I. Int J Obes 1992; 16: 999±1003. Research Alcohol and Alcoholism, 1987; suppl. 1, 6 Rosmond R, Lapidus L, Marin P, BjoÈrntorp P. Mental distress, 619±623. obesity and body fat distribution in middle-aged men. Obes 24 Kleinbaum DG. Logistic regression. A self-learning text. Res 1996; 4: 245±251. Springer Verlag: New York, 1994. 7 Dipietro L, Anda RF, Williamson DF, Stunkard AJ. Depres- 25 Grunberg NO, Straub RO. The role of gender and taste class in sive symptoms and weight change in a national cohort of the effects of stress on eating. Health Psychol 1992; 11: adults. Int J Obes 1992; 16: 745±753. 97±100. Predictors of major weight gain M Korkeila et al 957 26 Bellisle F, Louis-Sylvestre J, Linet N, Rocaboy B, Dalle B, 36 Kujala UM, Kaprio J, Sarna S, Koskenvuo M. Relationship of Cheneau F, L'Hinoret D, Gyot L. Anxiety and food intake in leisure-time physical activity and mortality. JAMA 1998; 279: men. Psychosom Med 1990; 52: 452±457. 440±444. 27 Baucom DH, Aiken PA. Effect of depressed mood on eating 37 Bouchard TJ. Genetic and environmental in¯uences on adult among obese and nonobese dieting and nondieting persons. personality: evaluating the evidence. In: Hettema J, Deary IJ J Pers Soc Psychology 1981; 41: 577±585. (eds). Foundations of Personality. Kluwer Academic Publish- 28 Schachter S, Goldman R, Gordon A. Effects of fear, food ers: Netherlands, 1993, pp 15±44. deprivation and obesity on eating. J Pers Soc Psychology 38 Perry GS, Byers TE, Mokdad AH, Serdula MK, Williamson 1968; 10: 91±97. DF. The validity of self reports on past body weights by US 29 Lowe MR, Fisher EB. Emotional reactivity, emotional eating, adults. Epidemiology 1995; 6: 61±66. and obesity: A naturalistic review. J Behav Med 1983; 6: 39 Kuskowska-Wolk A, Karlsson P, Stolt M, RoÈssner S. 135±149. The predictive validity of body mass index based on 30 Schlundt DG, Taylor D, Hill JO, Sbrocco T, Pope-Cordle J, self-reported weight and height. Int J Obes 1989; 13: Kasser T, Arnold D. A behavioral taxonomy of obese female 441±453. participants in a weight-loss program. Am J Clin Nutr 1991; 40 Fortenberry JD. Reliability of adolescents' reports of height 53: 1151±1158. and weight. J Adolesc Health Care 1992; 13: 114±117. 31 BjoÈrntorp P. The regulation of adipose tissue in humans. Int J 41 Casey VA, Dwyer JT, Berkey CS, Coleman KA, Gardner J, Obes 1996; 20: 291±302. Valdian I. Long-term memory of body weight and past weight 32 Foreyt JP, Brunner RL, Goodrick GK, Cutter G, Brownell KD, satisfaction ± a longitudinal follow-up study. Am J Clin Nutr Jeor St S. Psychological correlates of weight ¯uctuation. Int J 1991; 53: 1493±1498. Eating Disorder 1995; 17: 263±275. 42 Jalkanen L, Tuomilehto J, Tanskanen A, Puska P. Accuracy of 33 Rumpel C, Ingram DD, Harris TB, Madans J. The association self-reported body weight, compared to measured body between weight change and psychological well-being in weight. Scan J Soc Med 1987; 15: 191±198. women. Int J Obes 1994; 18: 179±183. 43 Concato J, Feinstein AR, Holford TR. The risk of determining 34 Rissanen A, HelioÈvaara M, Aromaa A. Overweight and risk with multivariable models. Ann Int Med 1993; 3: anthropometric changes in adulthood: a prospective study of 201±210. 17 000 Finns. Int J Obes 1988; 12: 391±401. 44 Power C, Manor O. Explaining social class differences in 35 Williamson DF, Kahn HS, Remington PL, Anda RF. The 10- psychological health among young adults: a longitudinal year incidence of overweight and major weight gain in US perspective. Soc Psychiatry Psychiatr Epidemiol 1992; 27: adults. Arch Int Med 1990; 150: 665±672. 284±291.