Weight gain and incident obesity among male snus users

Snus, a moist smokeless tobacco product used orally, is receiving growing attention in public health research and debate. This is probably due to the increasing use of the product and the ban on smoking in public areas.

Snus has historically been used mainly by men in Sweden, and to some extent in other Scandinavian countries [1]. However, it has now also reached new markets, for example the United States and South Africa [2]. The potential health effects of snus use have not been thoroughly investigated, and the relationship between the use of snus and metabolic processes such as the regulation of body weight is unclear. However, research on the effect of smoked tobacco (with an exposure to nicotine comparable with snus use) [3, 4] has found that smokers have a lower body mass index (BMI) than to non-smokers [5‐7], possibly as a consequence of increased energy expenditure. Smoking may also affect the body fat distribution and it is associated with abdominal obesity [6, 7], impaired glucose tolerance and insulin resistance [5‐7]. It is unclear whether the metabolic effects are due to nicotine or to other constituents in tobacco smoke [6]. With regard to snus use, one prospective study reported an association with the onset of obesity [8] while another failed to detect any differences in weight gain between snus users and non-tobacco users [9]. Results of cross-sectional studies of BMI [4, 9‐15] and abdominal obesity are conflicting [10, 15].

To contribute to an understanding of the potential role of snus use on changes in body weight, we studied the association between the use of snus and weight gain (≥ 5%) as well as incidence of obesity (BMI ≥30 kg/m²) during a five year follow-up among men in a population-based cohort study set in Stockholm County.

Baseline characteristics of the study participants are described in Table 1, and Figure 2 shows how the exposure categories concerning snus users were derived. In total, 18% of participants (n = 1,793) reported current snus use at baseline but among these only 839 were never-smokers (i.e. exclusive snus users). At follow-up, 445 were still exclusive snus users, 178 had quit using snus and 216 reported mixed tobacco use (i.e. both snus use and smoking). Such mixed use was categorised as "Other". This group also included mixed users at baseline and smokers in 2002 that began using snus during follow-up. Out of the 44% (n = 4,375) who had never used tobacco regularly at baseline, 3,877 were still never users of tobacco at follow-up. Fifty-two men had started using snus (categorised as "Began during follow-up").

In the group of stable snus users (n = 445, corresponding to 4.5%) the mean weight was 82.2 kilograms and the mean BMI was 25.2, which were slightly higher than the values for the never users of tobacco. On average, snus users were younger than both never users of tobacco and smokers. Regular physical activity during leisure time was more common in all categories of snus users compared to never users of tobacco and all smokers. Smokers in particular, but also stable current users of snus, less often reported a university degree, than never users of tobacco. An intermediate level of education was most common among the stable current users of snus. The proportion of heavy consumers of alcohol was higher among stable current users of snus than in any other group. Stable current users of snus and stable current smokers had less regular breakfast habits and were less often daily consumers of fruit and berries compared to all the other categories.

During follow-up, stable current snus users gained on average 1.9 kilograms, while never tobacco users gained 0.7 kilograms. The ORs for weight gain according to tobacco use are presented in Table 2. Stable current snus users had a moderately increased OR for weight gain, compared to never tobacco users, after adjustment for age, baseline weight, alcohol consumption, physical activity, education, consumption of fruit and berries, and frequency of having breakfast (OR = 1.31, 95% CI: 1.04-1.65). No significant associations were observed among stable former users of snus, or among men who quit or began using snus during follow-up. Smoking cessation was strongly associated with weight gain (OR = 3.15, 95% CI: 2.39-4.15) and a moderate association was seen among stable current users (OR = 1.24, 95% CI: 1.00-1.54). No associations were seen among stable former smokers or among those who began to smoke during follow-up.

Stable current snus use was associated with incident obesity (OR = 1.93, 95% CI: 1.13-3.30) (Table 3). Neither stable former use nor cessation during follow-up appeared to be associated with the development of obesity. No cases of obesity were observed among men who began to use snus during follow-up. Neither stable current nor stable former smoking was associated with incident obesity. However, quitting smoking during follow-up seemed to be associated with incident obesity (OR = 1.87, 95% CI: 0.99-3.53) as was the uptake of smoking (based on 6 cases).

In this study, based on a five-year follow-up of the Stockholm Public Health Cohort, the current use of snus was found to be moderately associated with weight gain and incident obesity. Previously, three longitudinal studies explored the association between snus use and weight. Two of these studies, both based on the Västerbotten Intervention Programme, reported results similar to ours. One observed that the heavy use of snus (>4 cans/week) was associated with incident obesity (OR = 1.70, 95% CI: 1.36-2.18), when the outcome was assessed 10 years after baseline [8]. In the second study, non-users of snus were reported to have a greater chance of maintaining their weight than snus users [16]. The third study found no differences in weight gain between exclusive snus users and non-users of tobacco [9]. However, in a cross-sectional analysis of the same study population, the prevalence ratio for BMI ≥27 among exclusive snus users was slightly elevated as compared to non-users of tobacco. Similarly, another cross-sectional study found that snus users had a higher prevalence of overweight (defined as BMI >26) than non-users of tobacco [12]. Further, one study found a higher mean BMI among snus users than among non-users [17], while four other studies found no differences in mean BMI [4, 10, 11, 14], of which two were partly based on the same study population [4, 11]. The use of snus has also been associated with obesity in a cross-sectional analysis of controls in a case-control study [13]. One study investigated the relationship between snus use and obesity based on three different measures (BMI ≥30, waist-hip-ratio ≥1.0 and waist circumference >102 centimetres) [15]. The researchers found no association between exclusive snus use and obesity based on any of these measures. However, a positive association between snus use and waist-hip-ratio has been reported previously [10].

The BMI at baseline did not differ between stable smokers and never users of tobacco, but the findings indicate that weight gain among smokers was higher than among never users of tobacco. This association persisted (although it was weakened) after adjusting for several life-style factors.

Discrepancies in results between different studies may be due to differences in sample size, differences in definition of exposure and/or outcome, or to differences in adjustment of potential confounders, especially cigarette smoking. Five studies presented results for exclusive snus users, (i.e. never smokers) [9, 11, 12, 14, 15], five included current and/or former smokers [4, 8, 10, 13, 17], whereof three presented results controlled for smoking [8, 13, 17]. One longitudinal study did not clearly report exclusion or adjustment for smoking [16]. Previous studies with large sample size (>10,000) and large numbers of exposed individuals (>700) all found a positive association between snus use and the respective outcome measure. These studies include the two longitudinal studies based on the Västerbotten Intervention Programme [8, 16], and two cross-sectional studies based on the Construction Workers Cohort [12] and the Malmö Diet and Cancer Study [17]. In studies of exclusive snus users, results were conflicting [9, 11, 12, 14, 15].

Little is known about the metabolic effects of snus use. However, cigarette smoking is associated with abdominal obesity [6, 7], increased cortisol secretion [18‐20] and a risk for type 2 diabetes [21]. If these metabolic effects can be attributed to the effect of nicotine on the central nervous system [20], it could be anticipated that they would be similar or more pronounced among snus users, due to similar levels of and sustained exposure to nicotine from this type of tobacco [3, 4]. Our finding, of very similar ORs for weight gain among stable current snus users and among stable current smokers, agrees with this hypothesis. Other similarities and differences between metabolic events among smokers and snus users are not easily interpreted. Associations with abdominal obesity [6, 7] and impaired glucose tolerance [5‐7, 21] have been documented for smoking. Among snus users, no increase in waist circumference [10, 15] but an increase in waist-hip-ratio [10] has been observed, and results regarding insulin resistance are ambiguous [4, 8, 11, 22, 23].

Obesity, overweight and changes in weight can be defined in several ways. We chose to define outcomes as weight gain ≥5% and as incidence of obesity. A weight gain of ≥5% is a suggested cut-off for clinically relevant gain [24]. Obesity, defined by the World Health Organisations as BMI ≥30 [7], is a component of the metabolic syndrome [25] and is often used in studies of weight and health outcomes. It is therefore both clinically relevant and enables comparison with other studies. BMI as a measure of body composition has limitations and does not consider the relative proportions of body fat or muscle mass. Nevertheless, among most individuals a BMI as high as 30 or above is unlikely to be due to muscle mass. The study is based on self-reported information. This is a potential source of bias, which however is likely to be non-differential with regard to tobacco exposure. The low participation rate at baseline, in line with other Swedish studies from the same years, could affect external validity. However, we have no reason to believe that the relationship between snus use and weight seen in this population would be different among men in the general population. Also, there is no reason to believe that attrition at follow-up was differential with regard to both exposure and outcome. The association between smoking cessation and weight gain, in line with previous studies [5, 26], suggests no major bias in our results. Strengths of this study include its prospective design and information on several covariates, making it possible to control for potential confounding. We had no information on energy intake, and cannot exclude the possibility of residual confounding. We attempted, however, to control for potential differences in eating habits using available information on the consumption of fruit and berries as well as information on the frequency of eating breakfast, both of which have been associated with energy balance and weight stability [27]. To our knowledge, this is the first study that has attempted to adjust for covariates related to energy intake.

Our findings suggest that snus use is moderately associated with weight gain and incident obesity. This indicates that there may be an increased risk for metabolic disturbances among snus users, a field that deserves further investigations.