ORIGINAL INVESTIGATION. Increase in Weight in All Birth Cohorts in a General Population

Increase in Weight in All Birth Cohorts in a General Population The Tromsø Study, 1974-1994 ORIGINAL INVESTIGATION Bjarne K. Jacobsen, PhD; Inger Njølstad, MD, PhD; Inger Thune, MD, PhD; Tom Wilsgaard, MSc; Maja-Lisa Løchen, MD, PhD; Henrik Schirmer, MD, PhD Background: Obesity is a risk factor for a number of chronic diseases. Few longitudinal studies have examined changes in body mass index ( [calculated as weight in kilograms divided by the square of the height in meters]). Objective: To investigate the changes in mean and the prevalence of obesity in a large cohort examined several times during a 20-year period. Methods: Mean, the percentage of subjects with low ( 20 kg/m 2 ), and the percentage who were obese ( 30 kg/m 2 ) were determined in a large population of men and women who were examined up to 4 times during a 20-year period (1974-1994/1995). In a longitudinal design, we observed 3541 men who attended all 4 screenings (1974-1994/1995) and 4993 women who attended the last 3 screenings (1979/ 1980-1994/1995). Results: The age- (25-49 years) and sex-adjusted mean increased 1 kg/m 2 in men from 1974 to 1994/1995 and 0.9 kg/m 2 in women from 1979/1980 to 1994/1995. In the last survey, subjects aged 25 to 85 years were included. In most age groups, the mean exceeded 25 kg/m 2 and the prevalence of obesity was 10% or higher in men and women aged 45 years or older. In the longitudinal analysis, the mean in men aged 20 to 49 years increased 2.0 kg/m 2 during 20 years of observation and increased 2.4 kg/m 2 in women aged 20 to 49 years during 15 years of observation. The increase in was larger in younger men than in older men. Conclusions: Body mass index increased in every examined birth cohort (1925-1964) during the 15- to 20- year observation period. Primary prevention of further increased body weight should be a priority. Arch Intern Med. 2001;161:466-472 From the Institute of Community Medicine, University of Tromsø, Tromsø, Norway. OBESITY IS a significant risk factor for a number of diseases, including cardiovascular diseases, type 2 diabetes mellitus, certain types of cancer, and osteoarthritis as well as mental distress. 1,2 Maintaining a lasting weight reduction is for many people an insurmountable task 3 ; therefore, the primary prevention of obesity, through a change in eating habits and/or an increase in physical activity, is an important objective for public health. It is therefore of great concern that the prevalence of obesity is increasing in most parts of the world. We are experiencing a global epidemic; often in the nonindustrialized world obesity occurs along with widespread malnourishment. 1,4 In the United States, the prevalence of being overweight in men and women aged 20 to 74 years has increased in the last 40 years. 5-7 The prevalence of obesity (body mass index [] 30 kg/m 2 ) was 10% in men and 15% in women in 1960/1961. Between 1988 and 1994, the prevalences were 20% and 25%, respectively. 5 The major increase in the prevalence of being overweight was observed in the last part of this 30-year period, between the second National Health and Nutrition Examination Survey (NHANES II, 1976-1980) and the third National Health and Nutrition Examination Survey(NHANESIII,1988-1994). 5,6 Recent data indicate that the prevalence of obesity in the United States is still increasing. 7 The age-standardized (35-64 years) prevalence of obesity in the European part of the World Health Organization (WHO)- MONICA survey (1983-1986) was 15% in men and 22% in women. 8,9 There were, however, large differences between the different survey centers. The highest prevalence was found among women in Kaunas, Lithuania (45%), and the lowest among men in Gothenburg, Sweden (7%). 8 The aim of this study was both to give longitudinal data about changes in in the same persons between 1974 and 1995, using data from 4 repeated measure- 466

SUBJECTS, MATERIALS, AND METHODS POPULATION The Tromsø Study was initiated in 1974 and is a singlecenter study of the population in the municipality of Tromsø. Tromsø is situated at the parallel of latitude that is 70 north of the equator (north of the Arctic Circle). 10-12 With approximately 60000 inhabitants, Tromsø is the largest city in northern Norway. The aims of the Tromsø Study are to investigate determinants of chronic diseases, to assess etiological significance, and to identify potentially modifiable determinants that might lead to the development of preventive strategies. The base for this study was men and women who attended 1 or more of the 4 surveys in the Tromsø Study in 1974, 1979/1980, 1986/1987, and 1994/1995. In 1974, all men aged 20 to 49 years were invited to the screening 10 ;in 1979/1980, the invited population was expanded to all men aged 20 to 54 years (thereby including the cohort examined in the first survey) and all women aged 20 to 49 years. 11 In the third screening (1986/1987), all men aged 20 to 61 years and all women aged 20 to 56 years were invited. 12 All individuals older than 24 years living in the Tromsø municipality were invited to the fourth survey in 1994/1995. After excluding subjects who were not able to attend (eg, because of temporary residence outside Tromsø), the attendance rate was 83% in 1974, 10 82% (men) and 88% (women) in 1979/1980, 11 and 76% (men) and 85% (women) in 1986/1987. 12 In 1994/1995, 74% of the invited men and 79% of the invited women attended the screening. In the analysis of data from the fourth survey in 1994/1995, we included men and women up to the age of 84 years. For older groups ( 85 years), attendance by mostly healthy persons was likely, as the 178 attendants represented only half of the population invited to the screening. All men and nonpregnant women who had their height and weight measured were included in the crosssectional analysis. Three percent of the attending women in 1986/1987 were pregnant. In 1974, data were available from 6579 men; in 1979/1980, from 8335 men and 7847 women; in 1986/1987, from 10403 men and 9853 women; and finally, in 1994/1995, from 12784 men and 13959 women. Two cohorts were observed in particular: the 3541 men who attended all 4 screenings and the 4993 women who attended the last 3 screenings. In addition, we have included in the cohort analyses 1189 men and 779 women who were too young to be included in all the surveys but took part in the surveys to which they were invited. Thus, both cross-sectional data and longitudinal data are presented in the tables. Age- and sex-adjusted values presented in Table 1 were calculated by applying the age- and sex-specific mean values to the population consisting of all the attendants of the 1986/1987 screening. MEASUREMENTS OF WEIGHT AND HEIGHT AND COMPUTATION OF At screening, height and weight were measured. Height (without shoes) was measured to the nearest centimeter. In the first survey, weight was measured to the nearest kilogram; in the next 3 surveys, to the nearest halfkilogram. Body mass index was calculated as weight in kilograms divided by the square of the height in meters. According to the WHO, 1 normal weight is a between 18.5 and 25 kg/m 2, overweight is a between 25 and 30 kg/m 2, and obesity is a at 30 kg/m 2 or higher. In the tables and figures, we have presented the mean in different age-sex strata as well as the percentage of subjects with relatively low ( 20 kg/m 2 ) and who are obese ( 30 kg/m 2 ). A lower than 20 kg/m 2 was selected as the indicator of low in our population because very few subjects in the Tromsø population are underweight as defined by the WHO ( 18.5 kg/m 2 ). 1 In our presentation, we will refer to these definitions of underweight, low, normal weight, overweight, and obese. STATISTICAL METHODS AND ETHICAL APPROVAL The statistical analyses were performed using the SAS package (SAS Institute Inc, Cary, NC; 1987). A P value less than.05 was considered statistically significant. The Regional Committee for Medical Research Ethics has approved the Tromsø Study. ments taken in Tromsø, Norway, and to describe the crosssectional distribution of according to age and sex in each of the 4 surveys. RESULTS Table 1 gives the results from the cross-sectional analyses. In general, the age-specific increased in men from one survey to the next, but in women, relatively small changes in were observed between 1979/ 1980 and 1986/1987. The sex- and age-adjusted (25-49 years) mean increased 1 kg/m 2 in men during the 20-year period of observation (corresponding to a 3-kg increase in weight in a man with a height of 1.75 m) and increased 0.9 kg/m 2 in women during the 15-year period of observation (approximately corresponding to a 2.5-kg increase in a woman with a height of 1.65 m). The SD of was higher in women than in men in all age groups (Table 1), and it increased with age in women. The percentage of underweight subjects ( 18.5 kg/m 2 ) was very low in men ( 1% in all 4 screenings). In women, it was somewhat higher (5%, 4%, and 2% in the screenings in 1979/1980, 1986/1987, and 1994/ 1995, respectively). The highest prevalence of underweight subjects (6%-9%) was found in younger women aged 20 to 29 years in the 1979/1980 and 1986/1987 screenings. In men, the prevalence of low ( 20 kg/m 2 ) was less than 10% except in the group aged 20 to 24 years. In women, a reduction in the percentage of the population with low occurred from 1979/1980 to 1994/ 1995 in relatively younger women (aged 39 years). The percentage of obese ( 30 kg/m 2 ) men and women 467

Table 1. Mean Body Mass Index () of Subjects and the Percentage With Low ( 20 kg/m 2 ) or Obesity ( 30 kg/m 2 ) by Age and Year Surveyed: The Tromsø Study, Norway* 1974, M/F 1979-1980, M/F Age, y No. Mean (SD) 20, % 30, % No. Mean (SD) 20, % 30, % 20-24 1012/x 22.6 (2.4)/x 11/x 1/x 1009/1307 22.8 (2.5)/21.5 (2.6) 10/30 1/1 25-29 1371/x 23.5 (2.7)/x 6/x 2/x 1450/1624 23.5 (2.7)/21.7 (2.6) 6/25 2/2 30-34 1318/x 24.0 (2.5)/x 3/x 2/x 1684/1724 24.3 (2.8)/22.4 (3.1) 4/20 3/3 35-39 1021/x 24.5 (2.7)/x 2/x 3/x 1411/1352 24.6 (2.6)/22.9 (3.2) 2/14 3/3 40-44 924/x 24.7 (2.9)/x 3/x 5/x 988/981 25.0 (2.7)/23.8 (3.5) 2/9 5/6 45-49 933/x 24.7 (2.9)/x 3/x 5/x 890/859 25.1 (3.0)/24.3 (3.7) 2/7 6/7 50-54 x/x x/x x/x x/x 903/x 25.1 (3.0)/x 2/x 6/x 55-59 x/x x/x x/x x/x x/x x/x x/x x/x 60-64 x/x x/x x/x x/x x/x x/x x/x x/x 65-69 x/x x/x x/x x/x x/x x/x x/x x/x 70-74 x/x x/x x/x x/x x/x x/x x/x x/x 75-79 x/x x/x x/x x/x x/x x/x x/x x/x 80-84 x/x x/x x/x x/x x/x x/x x/x x/x 20-49 (adj) 6579/x 24.0/x 5/x 3/x 7432/7847 24.2/22.7 4/17 3/3 20-54 (adj) x/x x/x x/x x/x 8335/x 24.3/x 4/x 3/x 25-49 (adj) 5567/x 24.3/x 3/x 3/x 6423/6540 24.5/22.9 3/15 4/4 25-54 (adj) x/x x/x x/x x/x 7326/x 24.5/x 3/x 4/x * is calculated as weight in kilograms divided by the square of the height in meters; x indicates not applicable; adj, age adjusted. For women in 1986-1987, 55-56 years. For men in 1986-1987, 60-61 years. Adjusted to the total population in the 1986-1987 survey. Table 2. The Population of Tromsø Aged 25 to 84 Years in 1994-1995 by Weight Classification: The Tromsø Study, Norway* Weight Classification, kg/m 2 Men, % Women, % Underweight 18.5 0.6 2.1 Low weight 18.5-19.9 2.0 6.2 Normal weight 20-24.9 43.5 51.9 Overweight 25-29.9 44.4 28.4 Obesity class I 30-34.9 8.3 9.1 Obesity class II + III 35 1.2 2.4 * indicates body mass index, calculated as weight in kilograms divided by the square of the height in meters. increased with age and from one survey to the next, particularly from the 1986/1987 survey to the survey conducted 8 years later. In the last survey (1994/1995), the mean was 25.6 kg/m 2 and 24.8 kg/m 2 in men and women, respectively. The increased with age in women. In men, the highest was observed around the age of 50 years in the cross-sectional analysis, and in relatively old men (aged 70 years or older), we observed a tendency toward a higher percentage of subjects with low s (Table 1). Table 2 shows that 9.5% of the men and 11.5% of the women were obese ( 30). Table 3 gives the results from the cohort of 3541 men aged 20 to 49 years in 1974 and observed for 20 years from 1974 to 1994/1995. We also included data from 1189 younger men (aged 10-19 years in 1974) who were observed from either 1979/1980 or 1986/1987 to 1994/ 1995. The mean in men aged 20 to 49 years in 1974 increased 2 kg/m 2 during the following 20 years. The birth cohort specific results are illustrated in a different way in Figure 1. Each line represents the same group of men in a 5-year birth cohort. A cohort effect of steeper increase in with increasing age was more evident in younger vs older cohorts. Men born in the early 1950s had, when they were 42 years old, approximately the same mean as men born in the late 1920s, when they were 67 years old. The prevalence of obesity ( 30 kg/ m 2 ) increased in all birth cohorts to 10% in 1994/1995 (Figure 2, Table 3). Table 4 details a significant increase in the in women during the 15 years between 1979/1980 and 1994/ 1995. The mean increase in in women aged 20 to 49 years in 1979/1980 was 2.4 kg/m 2. The increase in during the 15-year period between 1979/1980 and 1994/ 1995 was larger in women than in men in all birth cohorts. In women, the increased similarly between 1979/1980 and 1986/1987 in all birth cohorts, with a steeper increase in for all birth cohorts between the third and fourth survey (Table 4, Figure 1). In women born between 1955 and 1964, we found a higher at a given age. The prevalence of obesity increased more in the last part of the 15-year period than in the first part (Table 4, Figure 2). The median in the population was somewhat lower than the mean presented in the tables, particularly in women. For example, in 1974 the mean in men observed for 20 years was 24.0 kg/m 2 (Table 3), whereas the median was 23.8 kg/m 2. Similarly, in 1979/ 1980 the mean in women observed for 15 years was 22.7 kg/m 2 (Table 4) and the median was 22.1 kg/m 2. The median increase in during the 15 and 20 years of observation, respectively, was the same as the mean increase. The pattern of the cohort-specific changes in mean and median was quite similar in men, with a larger increase in the median in younger men (aged 20-29 468

1986-1987, M/F 1994-1995, M/F No. Mean (SD) 20,% 30,% No. Mean (SD) 20,% 30,% 1159/1229 23.2 (2.9)/22.1 (3.2) 11/25 3/3 x/x x/x x/x x/x 1317/1449 23.7 (2.7)/22.1 (3.1) 5/24 3/3 1511/1714 24.8 (3.2)/23.4 (3.7) 4/14 6/6 1583/1755 24.1 (2.9)/22.4 (3.1) 4/18 3/3 1555/1736 25.0 (3.2)/23.4 (3.7) 3/13 8/6 1709/1649 24.7 (3.0)/22.9 (3.1) 3/13 5/3 1649/1778 25.3 (3.1)/23.7 (3.7) 2/10 7/6 1484/1520 25.2 (2.9)/23.8 (3.6) 2/9 5/6 1680/1709 25.5 (3.2)/24.1 (3.6) 2/8 8/8 1074/1058 25.5 (2.9)/24.2 (3.6) 1/8 7/7 1599/1659 26.2 (3.4)/24.9 (4.0) 2/6 12/11 891/871 25.5 (3.1)/24.8 (3.8) 2/6 7/10 1304/1276 26.3 (3.2)/25.6 (4.4) 2/6 13/15 834/322 25.3 (3.3)/25.0 (4.1) 4/7 7/10 917/939 26.3 (3.2)/26.0 (4.4) 1/4 11/16 352/x 25.3 (3.0)/x 2/x 7/x 794/771 26.1 (3.5)/26.0 (4.4) 2/5 11/16 x/x x/x x/x x/x 690/853 25.8 (3.4)/26.6 (4.8) 3/5 12/21 x/x x/x x/x x/x 591/699 25.7 (3.7)/26.7 (4.6) 6/5 10/22 x/x x/x x/x x/x 343/535 25.5 (3.3)/26.8 (4.9) 6/7 9/24 x/x x/x x/x x/x 151/290 24.9 (3.5)/26.2 (4.5) 6/5 10/20 8326/8660 24.4/22.9 4/16 4/4 x/x x/x x/x x/x 9217/9531 24.5/23.1 4/15 5/4 x/x x/x x/x x/x 7167/7431 24.6/23.0 3/15 5/4 7994/8596 25.3/23.8 2/10 8/7 8058/8302 24.7/23.2 3/14 5/5 9298/9872 25.4/24.0 2/10 9/8 years) than in middle-aged men (aged 40-49 years) at baseline. In women generally there were some indications that the median increased somewhat less than the mean in younger women, with an opposite tendency in middle-aged women. Thus, among young women there is a stronger tendency for some obese women to increase the mean of the whole group than there is among middle-aged women. COMMENT The main finding in this study is that increased during the 15 to 20 years of follow-up in every examined birth cohort in this population-based study in Tromsø. In younger men, the increase in mean during the 20 years following 1974 was more pronounced than in older men. The increase in during the 15-year period from 1979/1980 to 1994/1995 was larger in women than in men, but the increase in in women differed little among the birth cohorts. Furthermore, the increased mean was not caused by an increase in in a minority of the population. Another salient finding in our study is the difference between the cross-sectional and longitudinal analyses. The former analysis indicates that the in men increases with age up to age 50 years, levels off, and then slowly decreases after age 60 years. The results from the cross-sectional analysis are in accordance with other crosssectional data. 13-15 The results from the longitudinal analysis, however, show that all birth cohorts have experienced an increase in weight. The cross-sectional and longitudinal results are compatible in that younger men have higher s than older men. Thus, in the 1974 survey, the mean increased directly with age in men aged 20 to 49 years. Twenty years later, when the men were 40 to 69 years old, the highest occurred in men aged 45 to 64 years and a somewhat lower mean occurred in men aged 65 to 69 years. When restricting the population in the 1994/1995 survey to subjects aged 35 to 64 years, we found that 10% to 11% of men and women were obese as defined by WHO. 1 Therefore, the prevalence of obesity in Tromsø, was somewhat lower in the mid-1990s than in most Western European countries as measured 10 years before in the WHO-MONICA survey in 1983-1986, 8 although lower prevalences of obesity have also been reported. 16 The prevalence of obesity in our population is also lower than in the United States 5 and in another county in Norway (the North-Trøndelag Health Surveys). 13 We have studied the change in in a relatively large population of both sexes measured 3 or 4 times during a 15- to 20-year period. Some comparable studies have been published. 15,17,18 Based on 2 measurements of in 17000 adult Finns taken an average of 5.7 years apart, Rissanen and colleagues 15 found that young men experienced a greater increase than young women. In middle-aged and older subjects (50 years or older at baseline in 1966-1972), the was unchanged or actually decreased between the 2 examinations. As their data 15 were collected before ours, comparisons are somewhat hampered. Williamson and colleagues 17 analyzed changes in in the United States during a 10-year period starting in 1971-1975 and included 3727 men and 6135 women. In the same age groups also considered in our analysis, Williamson and colleagues found that women experienced a greater increase than men, and younger subjects experienced a greater increase than older subjects. These results confirm some of ours. We found that women gained more 469

Table 3. Mean Body Mass Index () of 3541 Men Observed From 1974 to 1994/1995 by Age and Percentage With Low ( 20 kg/m 2 ) or Obesity ( 30 kg/m 2 ): The Tromsø Study, Norway* Age in 1974, y (No.) Mean 1974 1979/1980 1986/1987 1994/1995 20, % 30, % Mean 20, % 30, % Mean 20, % 30, % Mean 20, % 10-14 (689) x x x x x x 23.6 9 5 25.1 4 9 15-19 (500) x x x 22.8 8 1 24.1 3 4 25.3 2 8 20-24 (424) 22.9 8 1 23.7 4 3 24.6 2 5 25.7 1 10 25-29 (683) 23.6 6 2 24.4 3 3 25.1 3 6 26.2 2 11 30-34 (730) 24.0 3 1 24.6 2 3 25.2 1 5 26.2 1 10 35-39 (620) 24.5 1 3 24.9 1 4 25.4 1 6 26.2 1 12 40-44 (579) 24.6 3 4 25.0 1 5 25.4 3 7 26.1 2 11 45-49 (505) 24.6 2 4 25.0 1 4 25.3 1 6 25.7 2 10 20-49 (3541) 24.0 4 3 24.6 2 4 25.2 2 6 26.0 2 10 * is calculated as weight in kilograms divided by the square of the height in meters; x indicates not applicable. 30, % Mean, kg/m 2 27 25 23 A Birth Year 1960-1964 1955-1959 1950-1954 1945-1949 1940-1944 1935-1939 1930-1934 1925-1929 Percentage With 30 kg/m 2 18 15 12 9 6 3 A Birth Year 1960-1964 1955-1959 1950-1954 1945-1949 1940-1944 1935-1939 1930-1934 1925-1929 21 20 30 40 50 60 70 Age, y, at Screening, Men 27 B 0 20 30 40 50 60 70 Age, y, at Screening, Men 18 B 15 Mean, kg/m 2 25 23 Birth Year 1960-1964 1955-1959 1950-1954 1945-1949 1940-1944 1935-1939 1930-1934 Percentage With 30 kg/m 2 12 9 6 3 Birth Year 1960-1964 1955-1959 1950-1954 1945-1949 1940-1944 1935-1939 1930-1934 21 20 30 40 50 60 70 Age, y, at Screening, Women Figure 1. Mean body mass index () according to birth cohort in 3541 men observed from 1974 to 1994/1995 and 4993 women observed from 1979/1980 to 1994/1995: the Tromsø Study. 0 20 30 40 50 60 70 Age, y, at Screening, Women Figure 2. Prevalence of obesity (body mass index [] 30 kg/m 2 ) according to birth cohort in 3541 men observed from 1974 to 1994/1995 and 4993 women observed from 1979/1980 to 1994/1995: the Tromsø Study. weight than men did from 1979/1980 to 1994/1995, but that the change in weight in women was similar in the different birth cohorts. Williamson and colleagues found in subjects aged 55 years or older at baseline (older than the persons included in our longitudinal analysis) a decrease in the mean during the next 10-year period and a larger decrease in women than in men. This is similar to the findings by Rissanen and colleagues. 15 Recently, Lewis and colleagues 18 published a 10- year follow-up study (the Coronary Artery Risk Development in Young Adults [CARDIA] Study) of Americans aged 18 to 30 years at baseline in 1985/1986. A total of 5115 subjects were included in the baseline, 79% of whom were observed for 10 years. The mean and the prevalence of obesity have increased in both white and African American men and women in the 10 years after 1985/1986. The increase in was most pronounced in African American women, but the mean in all 4 race-sex groups in 1995/1996 (when the sub- 470

Table 4. Mean Body Mass Index () in Women Observed From 1979/1980 to 1994/1995 and Percentage With Low ( 20 kg/m 2 ) and Obesity ( 30 kg/m 2 ): The Tromsø Study, Norway* 1979/1980 1986/1987 1994/1995 Age in 1979/1980, y (No.) Mean 20, % 30, % Mean 20, % 30, % Mean 20, % 30, % 15-19 (779) x x x 22.0 26 2 23.6 13 6 20-24 (584) 21.4 29 1 22.1 22 2 23.7 10 6 25-29 (870) 21.7 23 2 22.5 14 3 24.1 7 7 30-34 (1129) 22.3 19 2 23.2 12 5 24.9 6 11 35-39 (989) 22.9 13 3 23.9 7 6 25.5 6 14 40-44 (761) 23.7 7 5 24.5 6 9 25.9 4 15 45-49 (660) 24.3 6 7 24.9 7 9 26.0 5 17 20-49 (4993) 22.7 16 3 23.5 11 6 25.1 6 11 * is calculated as weight in kilograms divided by the square of the height in meters; x indicates not applicable. jects were aged 28-40 years) was considerably higher than in subjects aged 30 to 39 years in our survey in 1995/ 1996. In terms of the prevalence of obesity, young adult Norwegians in Tromsø in 1994/1995 were comparable with young, white adult Americans in 1985/1986. Thune and colleagues 19 have previously shown that the mean increased in Tromsø during the 7 years after the screening in 1979/1980. No Norwegian data, however, have been available with regard to the change in weight in individuals observed during a long period. The changes in mean weight in repeated samples of Norwegian men and women aged 40 to 42 years have been presented by Tverdal. 20 He found a steady increase in in men from 1963-1972 to 1991-1995, whereas in women the decreased until 1977-1981 and then increased during the next 10 to 15 years from 1980. 20 The Norwegian North-Trøndelag Health Surveys showed that the mean increased from 1984-1986 to 1995/1996 for both men and women 20 years or older, and that the prevalence of obesity increased in all age groups younger than 90 years. 13 However, these results are also comparisons of data from 2 crosssectional studies, not longitudinal data. The increase in assessed from cross-sectional studies observed in our study is compatible with the results from most other European countries 1,8,21 and the United States. 5-7 Our results are based on measured, not selfreported, weight and height, thereby avoiding response bias in the computation of. In 1986/1987, was measured in 99% of the nonpregnant attendants, and in only 0.6% of the subjects was some deviation from the protocol (eg, measurement included shoes or relevant handicap) noted. However, some persons classified as overweight in our study may have a high because of physical training and a relatively high percentage of muscle rather than adipose tissue. The attendance rates of the screenings were relatively high, particularly of those that formed the basis for the 2 longitudinal analyses (83% for men in 1974 and 88% in women in 1979/1980). 10,11 This reduces the likelihood of major bias in the estimates of in the population. As must be expected in the longitudinal analysis with birth cohorts observed for up to 20 years, a relatively high percentage (46% in men) of the initial cohort did not take part in all surveys. Reasons for not attending one of the consecutive screenings include death, emigration from Tromsø, temporary absence from Tromsø, and unwillingness to participate. In this relatively young population, a lack of motivation and emigration are the main reasons, although the percentage that died during the next 20 years was not negligible in men aged 45 to 49 years. Because the characteristics of subjects who attended all screenings may differ from those who did not, a bias may be introduced. A total of 6579 men aged 20 to 49 years had their measured in 1974, whereas 3541 of these men (54%) had their measured in all 4 surveys. In the group aged 20 to 24 years in 1974, men who were observed during the next 20 years had a higher by 0.5 kg/m 2 than men who did not participate in all 4 screenings, whereas in men aged 45 to 49 years who participated throughout, the was lower by 0.4 kg/m 2. The implications of this for our main results, however, are not clear. Perhaps it indicates that the younger men who took part in all 4 surveys had a greater tendency to put on weight relative to the older men. We have no data to address this question formally, but found in the younger men (aged 20-24 years at baseline) who participated in all 4 screenings no correlation (r= 0.03) between the baseline and the change in during the next 20 years. In men aged 45 to 49 years at baseline, an inverse relationship was found (r= 0.2). Thus, there were no indications that men with high s at baseline tended to put on weight. It may also be suggested that the lower mean in men aged 45 to 49 years at baseline who attended all screenings reflects a higher mortality in the men who were most obese at baseline. However, the percentage of men in this age group who were obese differed little between all men in 1974 (5%; Table 1) and men who were observed for the entire 20-year period (4%; Table 3). In 1979/1980, 7847 nonpregnant women aged 20 to 49 years had their measured, whereas 4993 of these women (64%) had their measured in all 3 surveys. Analysis findings of the 6 different birth cohorts revealed that the mean in the women who did not attend all screenings did not differ significantly (P=.14-.97) from the in women who took part in all 3 screenings. Therefore, no bias with regard to the initial was indicated. 471

In the older age groups, the effect of a height reduction due to osteoporosis may somewhat influence the results from the longitudinal analysis. At a given weight, a reduced height would result in an increase in. A recent study has shown that in older age groups, the effect of height reduction on, given no actual change in weight, can be substantial (an increase of 2.5 kg/m 2 between the ages of 20 and 80 years in women). 22 During the 20 years from 1974 to 1994/1995, the mean height of the 505 oldest men observed (aged 45-49 years) was reduced by 14 mm. This corresponds to a 0.4-kg/m 2 increase in, considerably less than the observed 1.1-kg/m 2 increase. In the 660 women aged 45 to 49 years in 1979/1980 and observed for 15 years, there occurred a 10-mm reduction in height, corresponding to a 0.3-kg/m 2 increase in. Thus, in our study the change in body height cannot explain the change in during the follow-up period. Furthermore, with increasing age, the proportion of body weight being lean body mass normally decreases. Therefore, even if the weight of fat in the body is unchanged, the total body mass and are reduced. Thus, the 2 effects of aging (change in height due to osteoporosis and change in body composition) have opposing effects on. The most important implications of our findings are, of course, the effects that increased prevalence of obesity may have on the disease panorama in the years to come. It is noteworthy that this increase in body weight has taken place in age groups where has the strongest relation to mortality. 2 The mean values of in 1994/1995 exceed the optimal for longevity (20.0-24.9 kg/m 2 ) found for nonsmoking Americans with no history of disease. 2 It is, however, a paradox that although we demonstrate a significant increase in body weight in the period between 1974 and 1994/1995, the mortality rate of some of the diseases that may follow obesity (eg, cardiovascular diseases) is actually reduced. In another Norwegian county, the prevalence of self-reported diabetes mellitus increased in men younger than 90 years and in women younger than 60 years between 1984/1986 and 1995/1996. 11 Also in our population, the prevalence of diabetes was assessed by a selfadministered questionnaire. In subjects aged 40 to 49 years at baseline (the oldest age group that was examined in all surveys), we found the same incidence of diabetes from 1979/1980 to 1986/1987 as from 1986/1987 to 1995/ 1996. The incidence of diabetes in men from 1974 to 1979/ 1980 was, however, 40% lower (P=.10). We do not know the type of diabetes, but most new cases of diabetes in the group aged 40 to 49 years are of type 2 diabetes mellitus. In conclusion, we have described a distinct increase in the mean and median in all examined cohorts in Tromsø from 1974 to 1994/1995 (in men) and from 1979/1980 to 1994/1995 (in women). According to our results, the prevalence of obesity has increased in both men and women and is now approximately 10% in men 45 years or older and even higher in women 50 years or older. The pattern of the increase in seems to differ markedly between men and women. 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Diabetes in urban African Americans: functional health literacy of municipal hospital outpatients with diabetes. Diabetes Educ. 1997;23:563-568. Correction Errors in Comment Section. In the original investigation by Jacobsen et al titled Increase in Weight in All Birth Cohorts in a General Population, published in the February 12 issue of the ARCHIVES (2001;161:466-472), an error occurred in the Comment section on page 469. The fifth sentence in the second paragraph should have read: The cross-sectional and longitudinal results are compatible in that younger men have a larger increase in s than older men. Also, on page 472 the reference number in the fifth sentence of the second paragraph should have been 13 (Midthjell et al) and not 11 (Jacobsen and Thelle). (REPRINTED) ARCH INTERN MED/ VOL 161, JULY 9, 2001 1659