Body mass decrease after initial gain following smoking cessation

Transcription

1 International Epidemiological Association 1998 Printed in Great Britain International Journal of Epidemiology 1998;27: Body mass decrease after initial gain following smoking cessation Tetsuya Mizoue, a Ryoji Ueda, b Noritaka Tokui, a Yoshiyuki Hino b and Takesumi Yoshimura a Background Although smoking cessation is strongly associated with subsequent weight gain, it is not clear whether the initial gain in weight after smoking cessation remains over time. Method Results Cross-sectional analyses were made, using data from periodic health examinations for workers, on the relationship between body mass index (BMI) and the length of smoking cessation. In addition, linear regression coefficients of BMI on the length of cessation were estimated according to alcohol intake and sport activity, to examine the modifying effect of these factors on the weight of former smokers. Means of BMI were 23.1 kg/m 2, 23.3 kg/m 2, 23.6 kg/m 2 for light/medium smokers, heavy smokers and never smokers, respectively. Among former smokers who had smoked 25 cigarettes a day, odds ratio (OR) of BMI 25 kg/m 2 were 1.88 (95% confidence interval [CI] : ), 1.32 (95% CI : ), 0.66 (95% CI : ) for those with 2 4 years, 5 7 years, and 8 10 years of smoking cessation, respectively. The corresponding OR among those who previously consumed 25 cigarettes a day were 1.06 (95% CI : ), 1.00 (95% CI : ), and 1.49 (95% CI : ). Conclusions The results suggest that although heavy smokers may experience large weight gain and weigh more than never smokers in the few years after smoking cessation, they thereafter lose weight to the never smoker level, while light and moderate smokers gain weight up to the never smoker level without any excess after smoking cessation. Keywords Smoking cessation, body mass index, cross-sectional studies, alcohol drinking, exercise Accepted 6 May 1998 Cigarette smoking has been consistently identified as a risk factor in the development of cancer, atherosclerotic disease and a wide range of other diseases. 1 3 In addition, those who quit smoking have a lower mortality rate than continuing smokers. 4 5 Based on these findings various efforts have been made to encourage the general public to give up smoking. Body weight gain after smoking cessation, however, has been regarded as one of the main reasons for quitters to relapse, and fear of weight gain may inhibit any attempt to stop smoking. 6 Although quitters tended to gain weight and weighed more than continuing smokers as a result of smoking cessation, it would be likely that quitters did not exceed never smokers in weight in the long run since former smokers weighed as much a Department of Clinical Epidemiology, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu , Japan. b Nishinihon Occupational Health Service Centre, Japan. as lifetime non-smokers, 7 9 and quitters with long duration of smoking cessation approached in weight never smokers However, there have been discordant findings on body mass among past smokers in relation to cessation years. Chen et al. 18 found a decreasing trend in body mass with increasing years of cessation beginning 2 years after quitting, while Williamson et al. 15 observed increased risk of severe weight gain irrespective of the duration of cessation. Therefore, it is not clear whether weight gain in the short period after stopping smoking remains over time or not. Using data from worksite physical examinations on Japanese male civil servants we examined body mass relating to smoking status, especially focusing on cessation years among former smokers. The study questions are as follows: Does body mass decrease with increasing years of smoking cessation according to the number of cigarettes smoked a day before quitting? If so, do alcohol intake and sport activity modify the change in body mass after smoking cessation? 984

2 BODY MASS AFTER SMOKING CESSATION 985 Method Data source The data analysed were from worksite periodic health examinations of civil servants in the north-east part of Fukuoka prefecture, Japan. A total of 7324 workers were examined from April 1992 to March 1993 by Kitakyushu Industrial Health Clinic, Nishinihon Occupational Health Service Centre; one of the biggest health service providers for workers in Japan. This centre provides various types of health examination service, mainly at worksites, using mobile equipment. Body height and body weight Examinees underwent physical examination after overnight fasting. Height was measured using a vertical ruler, except for those aged 25 with a record of their height, which was revised every 5 years. Body weight was measured using a spring scale with examinees in light clothing and adjusted by subtracting 1 kg from the measured weight for clothes. Body mass index (BMI) was calculated as body weight (in kg) divided by the body height (in m 2 ). Those with BMI 25 or 28 were defined as having large body mass and extremely large body mass, respectively. Smoking and other covariates Information on personal habits was obtained from a selfadministered questionnaire. After smoking status was determined, current smokers were asked about daily consumption of cigarettes and duration of cigarette smoking in years, and former smokers were asked about cigarette consumption before quitting and duration of smoking cessation in years. Alcohol intake was determined by providing options for frequency of drinking per week, and for consumption per occasion. (Alcohol in go, a conventional unit of Japanese sake containing 27 ml of ethanol.) Frequency for any sport activity participated in was obtained by providing the options: never, less than twice a week, twice a week or more. Current smokers were defined as those smoking at least one cigarette a day for 5 years. Former smokers were defined as those who had smoked regularly at least one cigarette a day but had not smoked for over one year before the examination. Those who replied one year for the duration of cessation, however, were excluded from the analyses because they might include those who stopped smoking within one year. Former smokers were sub-divided according to cessation years; those who quit 2 4 years, 5 7 years, and 8 10 years ago. Subjects who had never smoked in their lives were classified as never smokers. Alcohol consumption was categorized into three levels: 12 go per week as heavy drinkers, 3 12 go as moderate drinkers, and 3 go as non/light drinkers. Subjects who participated in any sport activity twice a week or more were categorized in a group as doing habitual sport activity. Exclusions In this study only males aged (n = 3975) were analysed because of the low number of female former smokers and the relatively short duration of smoking for smokers in their twenties. Other exclusions were those who had missing data on smoking status (n = 8), current and former smokers with unknown number of cigarettes smoked (n = 23), current smokers with 5 years of smoking, including missing information (n = 89), former smokers with unknown cessation years (n = 15), and those unclear on sport activity (n = 20), alcohol intake (n = 11) or body weight (n = 3). Additional exclusions from former smokers were those who quit; within 1 year (n = 59), before 25 years old (n = 55) or 10 years ago (n = 227). The reason for the exclusion of the last group was that since they were about 5 years older (48.1 years) than the other smoking categories (current smokers, 42.6 years; non-smokers, 44.1 years; former smokers who quit 2 10 years ago, 43.6 years), the possibility of a cohort effect on body mass could not be eliminated. After the exclusions, 3541 subjects remained for the analyses. Statistical analysis Because cigarette consumption has been consistently identified as a factor related to both body mass among current smokers 7 9 and weight gain after smoking cessation, 9,11,12,14,15 separate analyses were made for those who smoked 1 24 cigarettes a day and for those smoked 25. Means of BMI and proportions of those with BMI 25 or 28 were calculated according to smoking status. Secondly, odds ratios (OR) and their 95% confidence intervals (CI) were estimated for large body mass (BMI 25) and for extremely large body mass (BMI 28) taking never smokers as controls, adjusted for age, alcohol intake and sport activity. Thirdly, age-adjusted linear regression coefficient of BMI on cessation years was calculated among former smokers with 2 10 years of cessation who previously smoked 25 cigarettes a day, according to alcohol intake and sport activity. The above calculations were performed using the Statistical Analysis System. 19 Results Table 1 shows basic characteristics according to smoking status. Heavy smokers who consumed 25 cigarettes were less prevalent among former smokers with longer duration of cessation. Former smokers were not so different in alcohol intake from current smokers but had a higher proportion of heavy drinkers than never smokers. The proportion of heavy drinkers decreased and moderate drinkers increased as cessation years increased. The proportion of those who engaged in habitual sport activity was much higher among former smokers than that among current smokers and was as high as that among never smokers. Table 2 shows means of BMI and proportions of those with BMI 25 or 28, according to smoking status and cigarettes consumption. Former smokers who consumed 1 24 cigarettes a day before quitting had a higher mean BMI and a higher proportion of large BMI than current smokers in the same category but had almost same values as never smokers. Among the past light/medium smokers, there was no clear trend in mean BMI or proportion of large BMI according to years of cessation, though the values were somewhat higher among those with 8 10 years of cessation. For the category of those who consumed 25 cigarettes a day, those who quit 2 4 years ago had a considerably higher mean BMI and a higher proportion of large BMI compared not only to current smokers but also to never smokers. In this group there was a decreasing trend in the mean BMI and proportion of those with large BMI with increasing years of cessation. The OR and their 95% CI for large body mass, taking never smokers as the reference, are presented in Table 3, according to

3 986 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY Table 1 Basic characteristics according to smoking status Former smokers (cessation years) Current smokers Never smokers n = 2291 n = 108 n = 134 n = 156 n = 852 Mean age (SE) 42.6 (0.2) 43.2 (0.8) 43.7 (0.7) 45.1 (0.6) 44.1 (0.3) No of cigarettes/day Alcohol intake a Non/light Medium Heavy Sport activity 2/week All figures in the Table are percentages except mean age. a Light, 3 go/week; medium, 3 12 go/week; heavy, 12 go/week. Table 2 Mean body mass index (BMI) and proportion (in percentage) of those with large body mass, according to the smoking status Former smokers (cessation years) Current smokers Never smokers 1 24 cigarettes/day n = 1251 n = 57 n = 75 n = 96 n = 852 Mean BMI (SE) 23.1 (0.1) 23.6 (0.3) 23.5 (0.3) 24.1 (0.3) 23.6 (0.1) BMI BMI cigarettes/day n = 1032 n = 51 n = 56 n = 54 n = 852 Mean BMI (SE) 23.3 (0.1) 24.8 (0.4) 23.9 (0.4) 23.3 (0.3) 23.6 (0.1) BMI BMI Table 3 Odds ratios (OR) and their 95% confidence intervals (CI) for large body mass according to number of cigarettes currently or previously smoked a day, adjusted for age, alcohol intake and sport activity Any amount of cigarettes BMI 25 BMI 28 OR 95% CI OR 95% CI Current smokers cigarettes/day Current smokers cigarettes/day Current smokers

4 BODY MASS AFTER SMOKING CESSATION 987 Table 4 Means a of body mass index (BMI) among those with 2 4 years of cessation, and the regression coefficients a of BMI on cessation years among those with 2 10 years of cessation, according to alcohol intake and sport activity, for former smokers who had smoked 25 cigarettes a day 2 4 years of cessation 2 10 years of cessation n mean (SE) of BMI n coefficient 95% CI Alcohol intake b Non/light (0.7) , Medium (0.7) , Heavy (0.8) , Sport activity 2 times/week (0.5) , times/week (0.9) , a Adjusted for age. b Light, 3 go/week; medium, 3 12 go/week; heavy, 12 go/week. number of cigarettes smoked a day. In the group who consumed 1 24 cigarettes a day, former smokers showed no increase in OR during 2 7 years of cessation, although those who quit 8 10 years ago had a somewhat increased OR. Current smokers had significantly decreased OR (BMI 25: OR = 0.79, 95% CI : ; BMI 28: OR = 0.66, 95% CI : ). For those who consumed 25 cigarettes a day, former smokers who quit 2 4 years before showed significantly elevated OR (BMI 25: OR = 1.88, 95% CI : ), while those quit 5 years before showed no such increase. Current smokers showed no decrease in OR. For assessing potential factors modifying body mass after smoking cessation, Table 4 shows linear regression coefficients of BMI on cessation years during 2 10 years of cessation, along with mean BMI during 2 4 years of cessation, according to alcohol intake and sport activity. This analysis was only made for those who consumed 25 cigarettes a day since a significant trend in BMI was not found in former smokers with lighter consumption. As alcohol consumption increased, BMI in the initial period increased and the coefficient decreased, with statistical significance in heavy alcohol drinkers (coefficient, 0.425; 95% CI : 0.740, 0.111). Little difference was observed in BMI in the initial period and the coefficient between those who engaged in sport activity and those who did not. Discussion The present study examined the relation of body mass to duration of smoking cessation in former smokers and found that the number of cigarettes smoked a day before quitting influenced the body mass; BMI in those who previously smoked 25 cigarettes a day was significantly greater than that of never smokers during the few years after smoking cessation. This was followed by a decrease to the never smoker level. However, the BMI in those who previously smoked 1 24 cigarettes a day did not differ greatly from that of never smokers, irrespective of the length of cessation. Body weight of those with a few years of smoking cessation could be determined by both weight before quitting and the amount of weight gain after smoking cessation. Body weight among current smokers showed a U-shaped pattern according to the amount of cigarettes smoked; 9,10 heavy and light smokers weigh almost the same as never smokers while medium smokers weigh least. The amount of weight gain after smoking cessation was positively related to the number of cigarettes smoked a day before quitting These facts support the finding in the present study that, during the few years after quitting smoking, only former smokers who had smoked large amounts of cigarettes showed excess body mass compared to never smokers. Cross-sectional analyses, 7 10 as well as follow-up studies over extended periods, revealed that former smokers weighed almost the same as never smokers. Therefore, it would be naturally expected that the excess weight in recent quitters who smoked a large number of cigarettes diminishes over an extended period, as the present study showed. Chen et al. 18 using cross-sectional data, found that body weight and BMI decreased with increasing years after smoking cessation, particularly in women. To the contrary, one longitudinal study showed the risk of severe weight gain remained high regardless of the duration of cessation. 15 These studies, however, did not take into consideration the amount of cigarettes previously smoked, which was consistently identified as a predictor of the amount of weight gain after smoking cessation. Dividing former smokers according to their past consumption of cigarettes, the present study detected both higher body mass than never smokers in the initial period and the subsequent decrease in body mass only among those who previously smoked 25 cigarettes a day. The present study found that, among former smokers who had smoked 25 cigarettes a day, those with higher alcohol consumption had a higher BMI than those who consumed less alcohol during the few years after smoking cessation. In addition, the study demonstrated that BMI among former smokers with heavy alcohol intake showed a decreasing trend with increasing years of smoking cessation. These results suggest that alcohol intake may enhance the weight gain over a definite period after smoking cessation, but the effect may diminish afterwards. To our knowledge, no previous study has examined this effect. Rodin 20 showed that those who gained weight after cessation ate carbohydrate significantly more than quitters whose weight remained stable, without any difference in total calorie intake. Therefore, if there was a dietary difference according to the alcohol intake category, the results in the present study might be confounded. Further study is needed on the independent

5 988 INTERNATIONAL JOURNAL OF EPIDEMIOLOGY association between alcohol intake and weight gain after smoking cessation. Inconsistent findings have been reported with regard to the effect of physical activity on weight gain after smoking cessation. Williamson et al. 15 indicated that regular physical activity at baseline was related to a somewhat higher risk for the subsequent large weight gain in males, while the same study showed a significantly lower risk in women. Terence et al. 16 reported no weight gain in quitters with habitual sport activity. Perkins et al. 21 reported greater thermic effect of nicotine in more fit and active males, suggesting greater weight gain in individuals with these characteristics after smoking cessation than others who quit. The present study found little difference in BMI during the initial period and linear regression coefficient of BMI on cessation years between those who presently participated in habitual sport activity and those who did not. This indicates that habitual sport activity does not modify the change in weight after smoking cessation. However, caution is necessary when interpreting this result since sport activity obtained in the present study was for post-cessation status. Future study should focus on the differential effect of physical activity both pre- and post-cessation on subsequent weight gain. This study had the following limitations. Firstly, interpretation of the present results from cross-sectional data was based on the assumption that former smokers when they quit had the same body mass as continuing smokers. Although it is not possible to confirm the assumption, separate analyses according to cigarette consumption, an identified factor related to body mass among current smokers, are comparable to some extent between the two groups. Secondly, if weight gain precipitated a relapse of smoking, former smokers with shorter periods of cessation might weigh more, or even less, than those with longer cessation periods. The present study excluded those who quit within one year, when quitters were at higher risk of relapsing to smoking than in subsequent periods, and thus this could minimize the effect of relapse. Thirdly, smoking status was determined by self-report. Although the smoking rate in Japan has been on the decrease, the proportion of current smokers among Japanese adult males was two-thirds 22 and, moreover, there was no legal restriction on advertising cigarette smoking through mass media at the time of the survey. Therefore, it is unlikely that ever smokers tended not to report or underreport their smoking status. In conclusion, although heavy smokers might experience large weight gain and weigh more then never smokers after smoking cessation, they thereafter lose weight to the never smokers level. 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