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Nutritional Epidemiology

Middle-Aged and Older Chinese Men and Women in Singapore Who Smoke Have Less Healthy Diets and Lifestyles than Nonsmokers¹

Department of Community, Occupational and Family Medicine, National University of Singapore, Singapore and ^* University of Minnesota Cancer Center, Minneapolis, MN 55455

²To whom correspondence should be addressed. E-mail: cofkwp{at}nus.edu.sg.

	ABSTRACT

TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
Although studies in Western populations have shown that smokers have decreased dietary intakes of antioxidants and other health-related nutrients, this has not been established in oriental populations. This study aimed to identify differences in dietary and lifestyle characteristics between current, former, and never-smokers among middle-aged and older Chinese in Singapore. The subjects, 45–74 y old, were participants in the Singapore Chinese Health Study, a prospective cohort that enrolled 63,257 (27,959 men and 35,298 women) Chinese in Singapore between 1993 and 1998. Data on current dietary habits (using a validated, semiquantitative FFQ) and other lifestyle factors were collected through face-to-face interviews. Mean daily intakes of various nutrients were estimated using a food composition table that was specifically developed for this population. The current smoking rates were 36% in men and 6% in women; an additional 22% of men and 3% of women were former smokers. In both sexes, current smokers were less educated, had lower BMI, led a more sedentary lifestyle, and drank more alcohol and coffee than those who never smoked. Current smokers had dose-dependent decreases in the intakes of a wide range of antioxidants, vitamins, fiber, and calcium, but increases in the intakes of cholesterol and nitrosamines compared with people who never smoked. Former smokers had dietary intakes that either were similar to never-smokers or intermediate between current and never-smokers. Our results are consistent with findings among Western populations, and suggest that the unhealthy diet and lifestyle in smokers occur across diverse cultures.

KEY WORDS: • cigarette smoking • nutrient intakes • physical activities • Chinese

Cigarette smoking is a major risk factor for multiple potentially fatal health outcomes, including cardiovascular and respiratory diseases, as well as cancers at various sites (1). Cigarette smoke contains a large number of oxidants and free radicals that contribute directly to carcinogenesis and atherogenesis; cigarette smoking accounts for an estimated 30% of all cancers and 20% of total deaths in developed countries (1,2). Studies in Western populations showed that smokers tend to have unhealthy food intake patterns, including consuming fewer fresh fruits and vegetables; therefore, they have lower intakes of nutrients such as vitamin C, fiber, folate, and carotenoids, which are believed to possess cancer-preventive and cardioprotective properties. Smokers also consume more alcohol and are more sedentary than those who never smoked (3–7). These undesirable dietary intake and lifestyle patterns may further enhance their risk of developing cardiovascular diseases and cancers. From a methodological viewpoint in epidemiology, these dietary differences across individuals with differing smoking status complicate the interpretation of any observed dietary effects on tobacco-related diseases.

Although the association between unhealthy dietary intakes and smoking seems to exist across populations in Western countries, there is a paucity of information from non-Western populations (8). One study involving 1010 Chinese men and women in Hong Kong reported that smokers did not vary in their dietary habits relative to those who never smoked (9). Because of the methodological limitations of that Chinese study, including the small number of female smokers (n = 19), the suboptimal statistical power to detect significant difference among male participants (68%), and possible missing food composition information as stated by the authors, caution should be exercised in the interpretation of these null results.

The present study examined the relations between lifestyle patterns, including diet and smoking status (never, former, and current), among participants of the Singapore Chinese Health Study, a population-based prospective cohort investigation of 63,000 Chinese men and women in Singapore.

	SUBJECTS AND METHODS

TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
    Study population. The subjects were participants in the Singapore Chinese Health Study, a population-based, prospective investigation of diet and cancer risk. From April 1993 through December 1998, a total of 63,257 Chinese women and men aged 45–74 y enrolled in the study (10). We restricted study subjects to the 2 major dialect groups of Chinese in Singapore, i.e., the Hokkiens, who originated from the southern part of Fujian Province, and the Cantonese, who came from the central region of Guangdong Province. The subjects were residents of government housing estates; 86% of the Singapore population resided in these facilities during the enrollment period. They were recruited by door-to-door invitation and 85% of eligible subjects who were invited responded positively. At recruitment, a face-to-face interview was conducted in the subject’s home by a trained interviewer using a structured, scanner-readable questionnaire, which requested information on demographics, lifetime use of tobacco, usual physical activity, menstrual and reproductive history (women only), medical history and family history of cancer. The questionnaire also included a dietary component assessing current intake patterns, which were subsequently validated against a series of 24-h diet recalls (10). The Institutional Review Boards at the University of Southern California and the National University of Singapore approved this study.

The study population was divided into never-, former, and current smokers based on their choice of 3 possible responses to the following question, "Have you ever smoked at least 1 cigarette a day for 1 y or longer?" Subjects who answered "no" were classified as "never-smokers," those who answered "yes, but I quit smoking" were classified as "former smokers," and those answered "yes, and I currently smoke" were classified as "current smokers." There were 6 predefined categories of average number of cigarettes smoked/d: 6 cigarettes, 7–12 cigarettes, 13–22 cigarettes, 23–32 cigarettes, 33–42 cigarettes, and 43 cigarettes. The number of years of active smoking was categorized as: 9 y, 10–19 y, 20–29 y, 30–39 y, and 40 y, whereas the number of years since quitting smoking for former smokers was categorized as: <1 y, 1–2 y, 3–4 y, 5–9 y, 10–14 y, 15–19 y, and 20 y.

    Baseline questionnaire. The development and validation of the baseline FFQ were described earlier (10). At recruitment, information on usual diet over the past 12 mo was obtained via this semiquantitative FFQ, which was administered in person at the subject’s home. The questionnaire listed 165 food and beverage items, and the respondent was asked to select from 8 food frequency categories (ranging from "never or hardly ever" to "2 or more times a day") and 3 portion sizes with accompanying photographs.

For the assessment of physical activity, subjects were asked to estimate the number of hours spent watching TV each day, and the numbers of hours each week spent on moderate activities such as brisk walking, bowling, bicycling on level ground, tai chi, or chi kung, and on strenuous sports such as jogging, bicycling on hills, tennis, squash, swimming laps, or aerobics.

    Statistical analysis. For each subject, we computed the mean daily intakes of roughly 100 nutritive and nonnutritive compounds by combining information obtained from the baseline interview with nutrient values provided in the Singapore Food Composition Table (10). All nutrients were expressed as weight per 1000 kJ or % energy to adjust for total energy intake.

Study subjects were classified according to demographic and other lifestyle variables by smoking status. ² statistics were used to examine the association between demographic/lifestyle factors and smoking status. Analysis of covariance (ANCOVA) was used to calculate the means of dietary nutrients and energy intake by various smoking categories after adjustment for age (continuous), BMI (continuous), education (no formal education, primary school, secondary school or higher), and dialect group (Cantonese or Hokkien). All analyses were performed separately for men and women. Due to the large study sample size, virtually all statistical comparisons reached the conventional level of significance (i.e., 2-sided P < 0.05). We proposed that an examination of the magnitude (in percentages) of the difference in diet between current, heavy smokers, and those who never smoked represents a more meaningful assessment of the potential association between diet and smoking. Statistical analysis was carried out using the SAS software version 8.2 (SAS Institute).

	RESULTS

TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 
In our study population, 36% of men and 6% of women were current cigarette smokers, whereas 22% of men and 3% of women were former smokers at enrollment. The remaining 42% of men and 91% of women never smoked cigarettes on a regular basis. In both genders, former smokers were older than either current or never-smokers. Independent of gender, current smokers had the lowest mean BMI. In both men and women, current smokers had the lowest level of education, whereas those who never smoked had the highest. Former smokers had levels between the 2 extremes in current and never-smokers, respectively. On the whole, women drank less alcohol than men. In both genders, use of cigarettes was positively correlated with alcohol consumption and coffee drinking. Tea consumption was comparable across all smoking categories (Table 1).

	DISCUSSION

TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

Our findings are consistent with those obtained in Western populations, including the United States, Canada, Europe, and Australia, which showed that those who never smoked in general have healthier dietary and lifestyle patterns compared with smokers (3,4,7,8,13–17). Because the Chinese culture is distinct from that in the West, our findings suggest that the diet-smoking association noted in diverse populations is not a culturally based phenomenon. The pertinent question is why smokers across all cultures eat differently from those who do not smoke. A possible explanation is that smokers are generally of a lower educational and income background than never-smokers, and are therefore less informed about healthy food choices or are unable to afford them (18,19). Our study does not support this explanation; all smoking-diet associations persisted after adjustment for level of education. Another possible explanation is that smokers are less health conscious than those who never smoked. Again, one would have to assume that this is a culture-free sentiment because we noted similar diet-smoking associations in this Chinese population whose culture and religious beliefs are distinct from their Western counterparts. In support of this hypothesis, our data also showed that another health-related behavior, physical activity, was much lower among smokers (Table 4).

Another possible explanation for the persistent difference in diet between smokers and never-smokers across diverse cultures and educational backgrounds is that there is a biological basis for this phenomenon. Studies showed that nicotine and other chemicals in cigarettes may affect food choices indirectly by altering the physiological processes relating to smell, taste, or appetite (20,21). Smokers have reported a decreased liking for sweet taste after smoking, and this may explain why smokers generally find sweet foods such as fruits and fruit juices less palatable than dried or processed foods (22). Those who stop smoking resume eating more fruits and vegetables (13,23), and it is possible that this is due to a physiologically based improvement in the senses of smell and taste. This notion, if confirmed, has implications in the design and implementation of an effective tobacco control program regardless of the culture and ethnicity of the target population.

Cigarette smoke contains many oxidants and free radicals, which can increase lipid peroxidation and induce oxidative damage to DNA (24,25). Smokers are therefore subjected to increased oxidative stress relative to nonsmokers. In other words, smokers actually require more antioxidants than those who never smoked to counter their heightened level of oxidative stress; an example of this is the higher recommended daily intake of vitamin C in the United States for smokers compared with that for nonsmokers (26). In our study, current smokers had dose-dependent decreases in intakes of fruits and fruit juices compared with those who never smoked; the difference between the current heavy smokers and those who never smoked was 33% in men and 37% in women (data not shown). The same pattern of differences was also seen in the consumption of all types of vegetables. It is possible that both taste aversion for fruits and vegetables and a poor attitude toward healthy living may act together to account for unhealthy dietary choices among smokers. If this is indeed the case, in addition to public education programs that aim to encourage consumption of fruit and vegetables, dietary supplements, or an attempt to remedy the altered taste response to foods through pharmacological means, may represent other options that could be effective in smokers. Finally, this study emphasizes the need to consider residual confounding effects when studying diet-disease associations in tobacco-related diseases.

	ACKNOWLEDGMENTS

 
We thank Ms. Siew-Hong Low for supervising the field work of the Singapore Chinese Health Study, and Ms. Kazuko Arakawa for the development and management of the cohort study database.

	FOOTNOTES

 
¹ Supported by National Institutes of Health grants R01 CA55069, R35 CA53890, and R01 CA80205 from the National Cancer Institute, Bethesda, MD.

Manuscript received 9 May 2005. Initial review completed 15 June 2005. Revision accepted 12 July 2005.

	LITERATURE CITED

TOP ABSTRACT SUBJECTS AND METHODS RESULTS DISCUSSION LITERATURE CITED

 

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