Smoking and unhealthy food habits

Transcription

1 EUROPEAN JOURNAL OF PUBLIC HEALTH 1998; 8: Smoking and unhealthy food habits How stable is the association? RITVA S. PRATTALA, MIKKO T. LAAKSONEN, OSSIJ. RAHKONEN * The aim of this study was to compare the food habits of male and female current smokers, ex-smokers and never-smokers in Do differences between smoking categories vary by study period or sociodemographic factors? The data were collected by mailed questionnaires in connection with a nationwide programme, 'Monitoring Health Behaviour among the Finnish Adult Population'. In this study, data from the years , and were used (n= 5,773-7,249, response rate 72-80%). Two examples of healthy food choices were included: avoidance of milk fat and daily use of vegetables. Cross-tabulation and logistic regression analysis were used to examine the effects of smoking, the time period and sociodemographic factors on food habits. Male and female smokers used vegetables and low-fat milk least often. -smokers alone or together with never-smokers most often avoided milk fat and used vegetables. Among men the differences between ex-smokers and current smokers increased. Among women the differences in the use of low-fat milk remained stable; in the use of vegetables, they first increased, then decreased. The differences in food habits between the smoking categories diminished when educational level was taken into account. After adjusting for place of residence and marital status, the association between smoking and diet persisted. Smokers tended to make unhealthy food choices, but the association varied by time period and gender. Between 1980 and 1995, Finnish male smokers seem to have become more consistent in their unhealthy behaviour, while a corresponding trend was not observed among women. Key words: food habits, lifestyle, smoking _} mokers eat differently from non-smokers. Generally, the diets of non-smokers follow dietary recommendations better than those of smokers, 1 " 3 typical foods eaten more by smokers are meat and white bread as well as beverages (including alcohol), whereas non-smokers eat more polyunsaturated margarines, fruit and vegetables. As a consequence, the intake of saturated fat and alcohol is higher and that of dietary fibre lower among smokers. With regard to diet, ex-smokers seem to be similar to those who have never smoked 3 " 5 or an intermediate group between them and current smokers, 6 "" 8 approaching the food habits of those who have never smoked since giving up. 4 ' 8 In some respects, however, ex-smokers are the group following the healthiest food habits. Whichelow et al. 9 showed that female ex-smokers used vegetables, 'brown' bread and semi-skimmed or skimmed milk more often than did women who had never smoked. Among men, a similar pattern was found only in the use of skimmed milk. Otherwise, those who had never smoked followed the dietary guidelines most closely and heavy smokers had the poorest diets of all. In Finland, food habits changed greatly between 1980 and The use of high-fat milk and butter has decreased * R.S. PrSttala 1, M.T. Laaksonen 1, O.J. Rahkonen 2 1 National Public Health Institute, Department of Epidemiology and Health Promotion, Health Education Research Unit, Helsinki, Finland 2 University of Helsinki. Department of Social Policy, Helsinki, Finland Correspondence: Ritva Prattala, PhD, National Public Health Institute, Department of Epidemiology and Health Promotion, Health Education Research Unit, Mannerheimintie 166, FIN-O03OO Helsinki, Finland, tel , fax , ritva.prattala ktl.fi and that of vegetables has increased. The changes have been observed among both men and women. Finnish men have followed the trend set by women with a time lag of five to ten years. Food habits have also changed in all socioeconomic groups. Class differences in food habits and fat intake that is, the proportion of saturated fat out of the total energy intake - have diminished since the early 1980s Contrary to trends in food habits, changes in the prevalence of smoking during the last 15 years have been small. Finnish men smoke more than women. However, among men smoking has decreased slightly, while among women it has increased. 12 Smoking varies by educational level, place of residence and marital status. and women having a lower educational level smoke more often and the differences have widened. 13 Urban women smoke more than those in rural areas and divorced persons smoke more than married or single people. 14 Thus, favourable changes in Finnish health behaviour have taken place in the area of diet but not in smoking. The contradictory trends might indicate a decreasing consistency in health behaviour, people adapting one healthy behaviour, for example the use of vegetables, while engaging in a second unhealthy one, that is smoking. Our previous analyses 15 showed that the consistency of health behaviour did not change greatly in Finland between 1982 and Male smokers, however, seemed to be more consistent in their unhealthy behaviour than were other Finnish men. The number of women having several unhealthy practices was too small for reliable conclusions. 16

2 Smoking and food habits The association of smoking and food habits implies that they are components of a greater entity, a lifestyle. A lifestyle involves an integrated set of orientations and practices such as routines of eating and habits of dress and, hence, has a certain unity. 17 ' 18 If an orientation towards health is a component of lifestyle, people should be consistent in their healthy or unhealthy behaviour. However, empirical studies do not show a strong relationship between various kinds of health behaviour except the association of smoking with other unhealthy behavi- Our.15,19-21 Previous studies on smoking and diet have been crosssectional except for a few short-term follow-up studies on those who have given up smoking. 22 ' 23 These studies do not shed light on the question of whether the association between smoking and diet remains unchanged when smoking and eating habits move in different directions in a population. In this paper we investigate the stability of the association between smoking and food habits. If smokers are increasingly prone to unhealthy behaviour, then changes towards a healthier diet should be less among them. The specific questions to be answered are as follows. Are there differences in the use of vegetables and milk between current smokers, ex-smokers and never-smokers? Are the differences similar in both men and women?. Were the differences similar in , and ? Does educational level, marital status or place of residence modify the associations between smoking and food habits? MATERIAL AND METHODS The data for our study were compiled by the National Public Health Institute in connection with a programme entitled 'Monitoring Health Behaviour among the Finnish Adult Population'. From 1978 a postal questionnaire was sent annually to a random sample of Finns between the ages of 15 and 64 years. 14 Six data sets from the years were pooled into three periods: , and The number of respondents was 7,249 in , 6,306 in and 5,773 in The response rates were 80%, 80% and 72% respectively. The index of smoking was formulated on the basis of two questions: i) Have you ever smoked? ii) When did you last smoke? Respondents who reported to have smoked cigarettes regularly or occasionally during the previous month were classified as current smokers. Those who reported to have last smoked over one month before were called ex-smokers. The others were never-smokers. Two indicators of 'healthy' food choices were included: avoidance of milk fat and daily use of vegetables. These choices are emphasized in the current Finnish dietary recommendations. The variable on the use of milk fat was based on the question what kind of milk do you usually drink? The multiple-choice answers were: 'full milk' (with 4.2% fat content), 'high-fat milk' (3.9% fat content), 'low-fat milk' (2.9% fat until 1982, and reduced to 1.9% in 1983), '1% milk', 'skimmed milk', and 'no milk at all'. The preliminary analyses showed that the changes and variation in the proportion of users of 1% milk, skimmed milk or no milk mirrored the proportion of those who used high-fat milk and butter. No additional information was obtained by using two variables describing the use of milk fat. Thus, only one variable was included in the final analyses. Those who reported usually drinking skimmed milk, 1% milk or no milk at all were grouped together and called as avoiders of milk fat. Vegetable consumption was measured by answers to the following question: how often have you eaten vegetables or root vegetables (potatoes exluded) during the last week in either a salad or as a separate dish? Participants reporting to have used vegetables at least six times during the previous week were considered daily users. Respondents younger than 25 years were excluded from the study, because in younger age groups health behaviour has probably not stabilized. The respondents were classified into four age groups: 25-34,35 44,45-54 and years. Educational level was divided into low (under 10 years), medium (10 12 years) and high (over 12 years). The respondents' places of residence were classified as urban, semi-urban or rural. Marital status was single, married or divorced/widowed. The distribution of smoking, food habits and the sociodemographic variables in the study population is presented in table 1. The data were analysed by cross-tabulation and multivariate logistic regression analyses (SPSS 24 ). Cross-tabulation was used to study the time trends in the use of milk and vegetables by smoking categories. The statistical significance of the change in the differences between the smoking categories was tested by the interaction of smoking and the time period (SAS 25 ). Multivariate logistic regressions were conducted to investigate further the association between smoking status and food habits. The avoidance of milk fat and the daily use of vegetables were the dependent variables. The analyses were performed separately for both food habits and for both sexes. The results are presented in odds ratios and 95% confidence intervals, relative to one category of each independent variable chosen as a reference, with a value of one., study period and age were first included in the models. Interactions were included if they were statistically significant and if the model including only the main effects did not fit to the data. In addition, the association of smoking and food choices was analysed separately for each study period. To elaborate the associations between smoking and food habits, educational level, marital status and place of residence were first added separately then simultaneously to the models including the effects of age group and smoking status. RESULTS smoked more often than women, but during the study period the proportion of male smokers decreased while that of female smokers increased. Food habits

3 EUROPEAN JOURNAL OF PUBLIC HEALTH VOL NO. 1 changed in a healthier direction and the level of education increased among the both sexes (table Avoidance of milk fat Figure 1 shows the age-adjusted trends in the use of milk fat among the three categories of smokers. The proportion of men and women who avoided milk fat increased remarkably from to (figure I and table 2). The direction of the change was similar in each smoker category for both sexes, but the differences between the smoker categories were not similar for men and women. I). In men, ex-smokers avoided milk fat most and current smokers least often, with never-smokers being the intermediate group (figure 1 and tables 2 and 3). The increase was larger among ex-smokers than current ones and, as a consequence, the difference between the ex-smokers and current smokers increased significantly from to (p=0.0004). Among women too, ex-smokers avoided milk fat most often, but the differences between the smoking categories did not change significantly. Contrary to the men, there was no difference in the use of milk fat between female current smokers and never-smokers (figure I and tables 2 and 3). Table 1 Distribution of smoking status, food habits and sociodemographic variables in the study population (%) (N=3,747) (N=3,502) (N=2,975) (N=3,331) (N=2,71O) (N=3,063) Use of vegetables Daily Avoidance of milk fat Yes Educational level Low Medium High Marital status Single Married Divorced/widowed Place of recidence Urban Semi-urban Rural Table 2 Odds ratios () and 95% confidence intervals (95% CI) of avoidance of milk fat and daily use of vegetables by smoking status, period and age group Study period group (years) (N=8,604) Avoidance of milk fat (N=9,032) 95% CI 95% CI ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) (N=8,869) Daily use of vegetables (N=9,429) 95% CI 95% CI ( ) ( ) ( ) ( ) (-1.30) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) Each model adjusted for other independent variables

4 Smoking and food habits Fat avoiders Vegetable users "' i- " " 20 ' Period Period Figure 1 -adjusted percentage of milk fat avoiders and daily users of vegetables by smoking status in , and among men ( ) and women ( ). smokers ( ), ex-smokers ( ) and those who have never smoked (A) Educational level had an impact on the associations between smoking and die avoidance of milk fat. Among both men and women the associations weakened slightly when the educational level was taken into account (table 3). When marital status or place of residence were added to the model separately or simultaneously the associations did not change any more than after adding educational level only (data not shown here). Daily use of vegetables As in the case of milk, a general trend towards healthier food habits could be seen in the use of vegetables, even though the changes in vegetable consumption were smaller (figure I and table 2). Differences between smoking categories were not quite the same for men and women and the differences were not stable during both study periods. Among men, current smokers used vegetables the least and consumption had not increased, whereas among exsmokers and never-smokers consumption had increased (figure 1 and tables 2 and 4). The difference between current and ex-smokers was significantly larger in than in (p=0.0002). Those who had never smoked and ex-smokers did not differ from each other in the use of vegetables. Among women, when all study periods were taken into account, ex-smokers were the group using vegetables the most and current smokers die least (table 2). In , there were no differences in the daily use of vegetables between the smoking categories (figure I and table 4) The use of vegetables increased in all groups between the first and second study period and it increased most among ex-smokers. In , ex-smokers used vegetables the most, never-smokers the least often and current smokers were the intermediate group. Between the second and third period, the increase continued only in the group of never-smokers. As a consequence, differences between the smoking categories first increased and then decreased. Between and , the use of vegetables among never-smokers reached the level of the exsmokers. In the former group used vegetables somewhat more than the others did. Table 3 Odds ratios () and 95% confidence intervals of avoidance of milk fat by smoking status and study period, adjusted for age group and educational level Period 1( ) Period 2 ( ) Period 3 ( ) ( ) (-1.65) ( ) ( ) ( ) ( ) and education (95% CD 1.49 ( ) 1.17 ( ) 1.73 ( ) 1.24 ( ) 1.69 ( ) 1.25 ( ) and education ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

5 EUROPEAN JOURNAL OF PUBLIC HEALTH VOL NO. 1 As in the case of milk, the association between smoking and the use of vegetables weakened when educational level was taken into account. Among women, the differences between smoking categories in the use of vegetables practically disappeared when educational level was taken into account (table 4). No additional effect was observed after controlling for the other sociodemographic variables (data not shown here). DISCUSSION There exists only a few data sources suitable for studies on trends in health behaviour. To our knowledge, this is the first time that associations between food habits and smoking have been analysed as time trends of several years. Our data might have some limitations. Since the beginning of the survey, response rates have decreased. If it is the case that respondents have healthier habits than non-respondents, the observed proportions of non-smokers, avoiders of milk fat and daily users of vegetables will be higher than those prevailing in the target population. Previous analyses based on the same survey material, however, have shown that the proportions of smokers or users of high-fat milk or butter do not vary with the response rate. 2^ Therefore, it can be assumed that our results are not significantly influenced by the response rate. If the decreasing response rate leads to any bias, the observed associations will become weaker than those in the target population. Classifying people into followers of a healthy versus an unhealthy diet is problematic because there are no objective criteria. The data used in our study do not give reliable estimates about the quantities of food consumption or nutrient intake. However, our results on changes and sociodemographic variation in food habits are in line with other Finnish information sources such as consumption statistics 28 or previous analyses using slightly different combinations of food questions. 10 The items selected as indicators of a 'healthy' diet are representative of satisfactory dietary habits according to the Finnish dietary recommendations. In line with previous studies,' 1 we found differences in the use of vegetables and milk between current smokers, ex-smokers and never-smokers. Although the differences were sometimes small and inconsistent, exsmokers alone or together with those who had never smoked were the group which most often made the healthy food choice. The associations between smoking and food choices weakened when educational level was taken into account. This was expected on the basis of previous analyses: men and women having a higher educational level smoke less but avoid dairy fat and use vegetables more often. ^ Systematic differences in food habits by educational level were observed in all smoking categories (data not shown). This implies that educational level is a more important determinant of food habits than is smoking. Previous studies have not compared the effect of smoking to other potential determinants of diet. In studies on the interrelationships of health behaviour, special attention should be paid to the modifying effects of educational level and other sociodemographic factors. seemed to be more consistent in their behaviour than were women. If men smoke, their eating habits are also unhealthy. Among men, the gap between smokers and never-smokers or ex-smokers increased from 1980 to For women, it seems to be easier to follow a healthy diet yet smoke. The idea of the consistency of unhealthy behaviour among Finnish smokers was discussed by Marti et al.- 52 who showed that the association of smoking and a low body-mass index had weakened between 1982 and They assumed that smokers, especially male smokers, had become more prone to unhealthy behaviour. Table 4 Odds ratios () and 95% confidence intervals of daily use of vegetables by smoking status and study period, adjusted for age group and educational level Period 1 ( ) Period 2 ( ) Period 3 ( ) ( ) ( ) ( ) ( ) ( ) ( ) and education ( ) ( ) ( ) ( ) ( ) ( ) and education ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )

6 Smoking and food habits The eclectic and contradictory behaviour we observed among Finnish women is typical of a late or post-modern lifestyle In post-traditional societies, lifestyle is characterized by individual choices within a plurality of options, even if socioeconomic circumstances still condition lifestyle choices. Health behaviour is no more a coherent pattern, either. However, Finnish men seemed to be more traditional than women; they behaved in either a healthy or unhealthy way. These contradictory trends among men and women show that behavioural change is the outcome of a complex interaction between individual beliefs, value systems and the social and cultural context in everyday life. 34 As an answer to the question in the title of this paper, we conclude that the association between smoking and food habits is both stable and unstable: smokers have a tendency to make unhealthy food choices, but the strength of the association changes with time and is different for men and women. The financial support of the Juho Vainio Research Foundation and the Adademy of Finland for the study is gratefully acknowledged. 1 Thompson RL, Margetts BM, Wood DA, Jackson AA. Cigarette smoking and food and nutrient intakes in relation to coronary heart disease. Nutr Res Rev 1992;5: Margetts BM, Jackson AA. Interactions between people's diet and their smoking habits: the dietary and nutritional survey of British adults. BMJ 1993;307: Subar AF, Harlan LC. 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