We found that people with diabetes in this insured population reported lower levels of current alcohol consumption than those that have been reported by the general US adult population. The prevalence of any alcohol consumption in the past year was 50.8% in adults with diabetes, compared with 61.9% reported in the 2002 National Health Interview Survey [40
]. This difference appeared to be as a result of the higher prevalence of former drinkers among people with diabetes compared with the general population (28.0 and 15.0%, respectively), as the prevalence of lifetime abstainers was nearly identical (21.2 and 22.1%, respectively). This suggests that people with diabetes may have curtailed their alcohol consumption because of declining health, perceived risk of alcohol on diabetes course [41
] or because of physician advice to limit alcohol intake [43
Alcohol use was associated with key self-care behaviours that are important for the health of patients with diabetes. We observed a gradient of increasing risk for poor adherence to diabetes self-care behaviours with increasing alcohol consumption, starting with those who consume even one drink a day. For use of exercise and smoking abstinence, we found statistically significant differences between lifetime abstainers and consumers of less than one drink a day and, for SMBG adherence, we found statistically significant differences between former drinkers and consumers of less than one drink a day. Former drinkers had the greatest compliance with each self-care behaviour, except current smoking. Our findings confirm those of previous investigators that former drinkers and lifetime abstainers have a different profile of risk behaviours [47
]. Former drinkers may include those who stopped drinking as a result of a perceived or actual worsening of diabetes disease course.
Our findings might be explained by alcohol consumption being a marker for a set of disadvantageous health-related behaviours. Alcohol use has been shown to be inversely associated with frequency of outpatient visits in the insured population from which the patients in our study were drawn [48
]. Alternatively, the disinhibitory effects or expectations of alcohol might explain poor adherence among regular, heavy drinkers. However, dis-inhibition would be less likely to explain differences among patients with low vs. moderate levels of alcohol consumption.
This is the largest study to date to examine the association of alcohol consumption with self-care behaviours within an ethnically diverse cohort of patients with diabetes. Because we had a high survey response rate of 83% and the demographic composition of our study population was representative of the general population, our findings are likely to reflect general patterns in insured patients with diabetes. Our findings extend those of past studies that found alcohol consumption was related to poorer compliance with diabetes self-care behaviours in more limited populations, including 154 older men treated at a Veterans Administration clinic [49
], 176 patients treated in a tertiary-care clinic in Mexico City [50
], and 392 minority patients at inner-city primary care clinics [51
]. The finding that alcohol consumption was consistently associated with poorer adherence with each of six diabetes self-care behaviours strengthens our conclusion that excess alcohol consumption may be detrimental to the health-care behaviours that improve control of diabetes.
Our study had several limitations. This cross-sectional study was designed to assess associations, not causation. Our study was not designed to determine the prevalence of alcohol use disorders. As with all human studies of the relationship between alcohol consumption and behaviours, randomization was not possible. Heavy alcohol consumption is likely to be a marker for a larger set of adverse health-care behaviours and risk factors. We relied on self report of alcohol consumption. If some of the heavy drinkers underreported their levels of alcohol consumption, this would have created a conservative bias (i.e. an underestimate of the gradient of association).
Our study findings have methodological implications for epidemiological studies of the effects of alcohol consumption on physiological outcomes such as glycaemic control, dyslipidaemia, and cardiovascular events. As an example, moderately increased alcohol consumption has been associated with lower risk of cardiovascular events, despite its associations with lower adherence to self-care behaviours. Thus, the estimates of the effect of alcohol consumption on cardiovascular events will be conservatively biased unless they control for confounding as a result of self-care behaviours, given that increasing alcohol consumption is associated with lower adherence to self-care behaviours, which in turn is associated with poorer glycaemic control, a predictor of diabetes complications.
We observed modestly reduced adherence to recommended self-care behaviours even in people with low to moderate alcohol consumption. Furthermore, this alcohol-behaviour gradient persisted even after adjustment for a wide variety of socio-economic, disease severity, and treatment variables. Our study highlights the importance of alcohol consumption as a marker and potential risk factor for poorer adherence to diabetes self-care behaviours. This suggests that diabetes health-care providers should routinely ask their patients about alcohol consumption and be aware that heavy consumption may be a marker for poor self-care behaviours, as well as for increased risk of alcohol use disorders.
Further study is warranted to assess whether physician advice to decrease alcohol consumption among heavy drinkers is associated with improved adherence to self-care recommendations and reduced risk for diabetes complications. Additionally, given the evidence that low to moderate alcohol intake may have cardiovascular benefits for patients with diabetes [52
], examination of the trade-offs between cardiovascular benefits vs. risk of lower adherence with self-care behaviours is needed. Similarly, clinical recommendations for alcohol consumption among people with diabetes need to balance the clinical benefits of moderate consumption and the potential risks of lowered adherence to self-care behaviours.