This study identified interaction effects of BMI and gender on predicting likelihood of lifetime and past-year alcohol use disorders and lifetime and past-year nicotine dependence. BMI was positively associated with lifetime risk for alcohol abuse and dependence in men and inversely associated with past-year risk in women. Overweight and obesity were associated with decreased odds for both lifetime and past-year nicotine dependence among men. Among women, overweight was associated with increased odds of lifetime nicotine dependence, and obesity was associated with decreased odds of past-year nicotine dependence. Overweight and obesity were not related to prevalence of lifetime or past-year illicit drug use disorders in either gender, with no significant interactions.
Our findings on BMI and alcohol use disorders are consistent with other studies examining associations between alcohol consumption and body weight. Prior research suggests that men who consume alcohol do not consume fewer calories from other food sources than men who do not drink (Colditz et al., 1991
). It is therefore not surprising that men with alcohol use disorders, who in most cases consume higher quantities of alcohol than men without disordered drinking, should be heavier than their counterparts without alcohol use disorders. The lack of association with past-year alcohol use disorders may reflect a gradual process of alcohol associated weight gain in men. Nicotine and/or drug use appear to attenuate the relationship between BMI and alcohol dependence, as the association was no longer significant when they were removed as covariates.
The inverse association between BMI and past-year alcohol use disorders among women is consistent with previous studies showing negative associations between quantity of alcohol consumed and BMI in women in the general population. Prior research also suggests that women who consume alcohol substitute alcohol calories for other sources of energy (Colditz et al., 1991
). If decreased caloric intake explains lower body weight among women with alcohol use disorders, effects of reduced food intake on body weight could be temporary. This could explain why the category of women with lifetime alcohol use disorders, most of whom do not currently meet criteria, do not differ from women without a history of problem alcohol use. The failure to find an association between BMI and alcohol dependence may indicate that women who drink most heavily are consuming excessive calories from alcohol, thereby replacing calories avoided through reduction in food intake. Removing nicotine dependence and drug use disorder covariates resulted in a significant negative association between obesity and past-year alcohol dependence, suggesting that the alcohol dependent women who smoke or use illicit drugs may consume fewer calories than those who do not.
BMI was not associated with risk for illicit drug use disorders in general or any specific drug use disorder. Although there was a trend toward increased risk for lifetime opiate use disorders among overweight women, the association between BMI and risk for opiate use disorders was not significant. Our results do not support the commonly held belief that opiate abuse leads to weight loss (Torpy, 2004
Marijuana enhances appetite, and medications based on its main psychoactive ingredient, tetrahydrocannabanol (THC), have been used to improve appetite and restore body weight in patients with AIDS-related wasting (Wilkins, 2006
). Cocaine suppresses appetite, and there is evidence that desire for weight control motivates many cocaine users, particularly women (Cochrane, Malcolm, & Brewerton, 1998
). Although this study did not examine drug effects on appetite, marijuana and cocaine use disorders are not related to body weight in this large epidemiologic sample.
It is unclear why relationships between BMI and nicotine dependence were more robust and consistent for men compared to women. Given the findings in men, it is not surprising that obese women were less likely than normal weight women to have past-year nicotine dependence. The fact that overweight women were more
likely to have a lifetime history of nicotine dependence is a bit more puzzling
. Nicotine use is generally associated with weight loss (Schechter & Cook, 1976
), and cessation of use is associated with weight gain (Caan et al., 1996
; Klesges et al., 1997
). Male smokers generally smoke more cigarettes per day than female smokers (Etter, Prokhorov, & Perneger, 2002
). By smoking fewer cigarettes per day, female smokers may decrease exposure to nicotine’s effects on appetite or metabolism. In the NESARC sample, male smokers with past-year nicotine dependence smoked an average of 19.5 cigarettes per day compared to 17.2 per day for past-year female smokers, and the difference was statistically significant (F=32.2, p
<.001). It is therefore possible that the level of nicotine absorbed by women who currently smoke is sufficient to avoid obesity but not overweight. The category of lifetime nicotine dependence includes former smokers, so the higher risk among overweight women could be due to post-cessation weight gain, a problem that affects women more frequently than men (O'Hara et al., 1998
Although scientists have long speculated, and evidence increasingly shows, that similar brain mechanisms underlie addictions to alcohol, drugs, and nicotine and excessive food intake (Grigson, 2002
; Simansky, 2005
; Volkow & Wise, 2005
), only a handful of studies have looked at associations between overweight and obesity and various substance use disorders. Negative associations between substance use disorders and overweight and/or obesity would support the hypothesis that compulsive overeating and compulsive use of substances compete for the same reward systems in the brain. Our results do not provide consistently strong support for this hypothesis. Our findings suggest that excessive and dysfunctional substance use can co-occur with overweight and obesity, and in some cases the risk for substance use disorders is elevated among individuals with higher BMI. It therefore appears that many individuals with substance use disorders are sensitive to the rewarding properties of both psychoactive substances and food. Gender differences in relationships between BMI and substance use disorders require further investigation. For instance, although prior research indicates that women who drink alcohol consume fewer calories from other sources (Colditz et al., 1991
), it is not clear why alcohol calories replace food calories among women but not men.
Strengths of this study include the large sample size, careful diagnosis of DSM-IV substance use disorders, and evaluation of a range of specific substance use disorders. We were also able to control for a variety of other psychiatric disorders that may independently impact BMI and substance use disorders. Weaknesses of this study must be acknowledged. It is a cross sectional study and therefore does not provide information about the direction of causality. Although prior research suggests that use of various substances can affect body weight, the possibility that overweight and obesity enhance or attenuate risk for various substance use disorders, rather than the other way around, can not be ruled out. Although it used a large, representative sample of U.S. adults, this study, like most prior epidemiologic studies examining substance use disorders, included relatively small numbers of individuals with specific drug use disorders. It is therefore possible that some null findings for specific drug use disorders were due to insufficient power. Another concern is that self-reported height and weight were used to calculate BMI, which could lead to underestimation (Flood, Webb, Lazarus, & Pang, 2000
; Kuczmarski, Kuczmarski, & Najjar, 2001
). Finally, one strength of this study, the large sample, can also be viewed as a weakness. With samples this large, even fairly small effects are significant, and their clinical significance may be questionable. Some of the significant odds ratios we found are fairly modest, but in the population as a whole, even a modestly increased risk for substance use disorders can have detectable effects in terms of costs to society, such as treatment costs, associated medical costs and effects on crime.
Our findings on associations of BMI with past-year substance use disorders differ somewhat from those of Pickering et al. (2007)
using the same sample, which we believe resulted from methodological differences between their study and ours. Pickering et al. (2007)
divided their obese sample further into obese and extremely obese subsamples, and dividing the sample in this way could have reduced the likelihood of identifying significant findings as the number of extremely obese respondents was small, particularly when the sample was further divided by gender. In addition, those authors controlled for a number of additional covariates including eleven past-year medical conditions, and twelve past-year stressful life events. We chose not to control for these variables because both overweight/obesity and substance use disorders appear to increase risk for medical conditions and many of the life stressors examined rather than be caused by them (Chou, Grant, & Dawson, 1996
; Klein et al., 2004
; Laitinen, Power, Ek, Sovio, & Jarvelin, 2002
; Pingitore, Dugoni, Tindale, & Spring, 1994
; Poirier et al., 2006
; Rohde et al., 2007
; Stein, 1999
). Although controlling for all possible contributing variables is a rigorous and appropriate approach to examining causal relationships, we felt it would mask some genuine associations in this study of population associations between the conditions of interest.
In conclusion, we found both positive and negative associations of BMI with various substance use disorders, and significant gender differences in those relationships. Further research is needed to identify potential reasons for gender differences and to understand potential neurological, metabolic, and psychosocial contributions to the different relationships among men and women.