Gender-Specific Association between Tobacco Smoking and Central Obesity among 0.5 Million Chinese People: The China Kadoorie Biobank Study

Abstract

ObjectivesLifestyle factors are well-known important modifiable risk factors for obesity; the association between tobacco smoking and central obesity, however, is largely unknown in the Chinese population. This study examined the relationship between smoking and central obesity in 0.5 million Chinese adults, a population with a low prevalence of general obesity, but a high prevalence of central obesity.SubjectsA total of 487,527 adults (200,564 males and 286,963 females), aged 30-79 years, were enrolled in the baseline survey of the China Kadoorie Biobank (CKB) Study conducted during 2004-2008. Waist circumference (WC) and WC/height ratio (WHtR) were used as measures of central obesity.ResultsThe prevalence of regular smokers was significantly higher among males (60.6%) than among females (2.2%). The prevalence of central obesity increased with age and BMI levels, with a significant gender difference (females>males). Of note, almost all obese adults (99.4%) were centrally obese regardless of gender. In multivariable regression analyses, adjusting for age, education, physical activity, alcohol use and survey site, regular smoking was inversely associated with BMI in males (standardized regression coefficients, β= -0.093, p<0.001) and females (β= -0.025, p<0.001). Of interest, in the BMI stratification analyses in 18 groups, all βs of regular smoking for WHtR were positive in both genders; the βs showed a significantly greater increasing trend with increasing BMI in males than in females. In the analyses with model adjustment for BMI, the positive associations between regular smoking and WHtR were stronger in males (β= 0.021, p<0.001) than in females (β= 0.008, p<0.001) (p<0.001 for gender difference). WC showed considerably consistent results.ConclusionsThe data indicate that tobacco smoking is an important risk factor for central obesity, but the association is gender-specific and depends on the adjustment for general obesity.

Trends in the association between smoking history and general/central obesity in Catalonia, Spain (1992-2003)

“…A recent large cohort study in the Chinese adult population has also shown that tobacco smoking is an important risk factor for central obesity. However, the positive association of regular smoking with WC was observed especially in male normal-weight adults after adjustment for BMI (4). Again, changes in associations at different points in time have not been reported previously, but our results in men suggest that disparities between current smokers and never smokers are diminished as levels of central obesity rise among the never smokers.…”

“…With some exceptions indicating no association (3), the majority of studies on this topic have found negative associations between current smoking -especially moderate and heavy smoking-and general obesity (2,4,13,26,27). No previous studies have looked at changes in associations coinciding with shifts in the prevalence of obesity and smoking over time.…”

“…In men, VAT increases when testosterone concentration decreases (35), and testosterone administration in middle-aged men reduces VAT by increasing lipolysis (36); in addition, smoking may reduce testosterone concentrations (35,36). However, in the case of heavy smokers, the mentioned increase in metabolism induced by nicotine might be outweighed by the metabolic effects of nicotine that favour abdominal fat accumulation and the smokers propensity for unhealthy lifestyle habits, thus causing a direct relationship for heavy smokers and WC as compared to light smokers (4,5).…”

“…Smoking cessation has been associated with increased risk of weight gain (2). In addition, it has been suggested that current smoking -particularly of high intensity-may increase insulin resistance and may thus be associated with central fat accumulation (3,4), which could increase the risk of diabetes and metabolic syndrome and, hence, the risk of cardiovascular disease (5,6). Thus in addition to more direct pathways, smoking may also contribute to morbidity and mortality indirectly through an influence on obesity, particularly as numerous studies suggest that central fatness is a more important determinant of disease risk than is generalized obesity (7).…”

“…Although the literature on the obesity-smoking relationship is accumulating (4,5,(11)(12)(13), a greater pool of evidence is needed, especially on the central obesity-smoking relationship, with some very recent studies in Asian populations among which the prevalence of central obesity is greater than that of Caucasians (4,13). In particular, it is crucial to explore both the emerging evidence that central fatness and current heavy smoking may co-occur, and of the attenuation over the longer term of the weight status-smoking cessation relationship.…”