4.1. Summary of the results
This analytical cross-sectional study highlights the association between harmful alcohol consumption (AUDIT-C score ≥5) and obesity (BMI, WC). The prevalence of overweight and obesity among the study population was more than 60%. Alcohol consumption was prevalent in this study sample, with nearly 9 out of 10 participants (86.5%) reporting alcohol consumption. Less than one-quarter of alcohol drinkers drank three or more times a week, and almost one-third of drinkers engaged in binge drinking at least one time per week. Nearly half of the participants (49.1%) who completed the AUDIT-C questionnaire had harmful alcohol consumption patterns.
In the univariate analysis, all the sociodemographic variables and most of the health-related variables showed significant associations with WC and BMI. Drinking status was significantly associated with BMI but not with WC. Obesity and overweight were significantly associated with alcohol consumption (78.5% and 84.2%, respectively, p<0.001). Those who drank frequently (≥ 3 times a week) were less likely to be obese and overweight (23.9% and 22.9%, respectively) than those who drank less frequently. However, this difference was not statistically significant. In contrast with participants who engaged in binge drinking less than once per week, over one-third of those who indulged in more frequent binge drinking were obese (35.9%, p < 0.001). Harmful drinkers had a larger WC (93.4±13.86 cm, p<0.001) and were significantly more obese (48.2%, p<0.001) than nonharmful drinkers.
The results of the multivariable linear regression analysis revealed a positive association between harmful alcohol consumption and WC after adjustment for sociodemographic and health-related factors. However, after controlling for other alcohol-related variables (frequency of alcohol intake and binge drinking), this association became nonsignificant. On the other hand, those who frequently binge drank (≥ 1 time per week) had a WC 2.03 times bigger than those who binge drank less frequently (β = 2.03, 95% CI: 0.89, 3.17). Additionally, an inverse association between alcohol consumption frequency and mean WC was observed; however, this association was not statistically significant. In the multivariable logistic regression analysis, participants who scored 5 or higher on the AUDIT-C questionnaire had higher odds of overweight/obesity than nonharmful drinkers. Age, sex, marital status, education level, employment status, general health condition, and frequency of fruit consumption were all significantly and independently associated with BMI.
4.2. Data interpretation
4.2.1. Harmful alcohol consumption and obesity
The current study showed positive associations between harmful alcohol consumption (assessed with the AUDIT-C questionnaire) and obesity indicators (both BMI and WC) after controlling for sociodemographic and health-related factors. After further controlling for binge drinking and alcohol consumption frequency, the association between harmful alcohol consumption and obesity (WC) was no longer significant. Most studies on obesity looked at either the frequency or quantity of alcohol consumed, or both, but did not use the AUDIT-C questionnaire to investigate this association. To the best of author knowledge, this is the first study to examine the association between harmful alcohol consumption, using the AUDIT-C, and obesity in a sample of the Irish population. Since the AUDIT-C is a standardized screening instrument that identifies harmful alcohol consumption in primary health care settings, it can be utilized as a tool in future studies on the association between alcohol consumption and obesity and help further validate the controversial evidence of this association.
4.2.2. Frequency of alcohol consumption and obesity
Although the current study showed an inverse association between alcohol consumption frequency and mean WC, this association was not statistically significant (β = -0.19 95% CI: -1.44, 1.06). This nonsignificant association could be attributed to the small proportion of the study population who consumed alcohol at least three times per week (n=886, 22.5%); thus, it was difficult to obtain a significant result. Examining the association between frequency of alcohol consumption and BMI was not possible, as the fully adjusted model showed poor model fit (Hosmer–Lemeshow p = 0.002 and Nagelkerke R2= 0.126). Previous studies examined the association between alcohol frequency and obesity, and the results were discordant. Some studies found inverse associations between the frequency of alcohol consumption and obesity indicators (BMI and WC) in both sexes (5-7). Dumesnil et al. (5), found that the inverse association between the frequency of alcohol intake and obesity existed regardless of total alcohol intake (6). O'Donovan et al. (5), on the other hand, discovered a bell-shaped association between the frequency of alcohol consumption and obesity, with no difference in risk observed between those who never drank and those who drank the most frequently. Several factors could explain such an inverse relationship between alcohol frequency and obesity. First, alcohol intake might affect macronutrient absorption, leading to reduced energy intake. Furthermore, alcohol consumption may stimulate thermogenesis by activating the ethanol oxidizing system, which can result in weight loss (16). Park et al. (10), on the other hand, found no association between the frequency of alcohol consumption and abdominal obesity in individuals with normal weight. However, this lack of an association could be related to the lower prevalence of abdominal obesity in the study population, < 8% in both sex; thus, an exact association might be difficult to obtain. Overall, based on the current evidence, the promotion of the consumption of alcohol to reduce the risk of obesity is not advisable, as the exact mechanism is not well explored.
4.2.3. Binge drinking and obesity
Binge drinking was also examined in this study, and the results showed that those who frequently engaged in binge drinking (≥ 1 time per week) had a larger mean WC than those who engaged in binge drinking less frequently. Most of the studies conducted on the association between binge drinking and obesity have shown positive associations. A Korean study conducted in normal weight; middle-aged adults of both sexes showed that those who engaged in daily binge drinking had a significantly higher rate of abdominal obesity (WC) than those who engaged in binge drinking less frequently (10). Similarly, a dose–response relationship between binge drinking and obesity was found by Arif and Rohrer, (17). Tolestrup et al. (5) found that binge drinkers were 77% more likely to be obese (OR= 1.77, 95%: 1.18, 2.65) than nonbinge drinkers. Rohrer et al. (8), on the other hand, used BMI to examine the relationship between the frequency of binge drinking and obesity in nonsmoking participants in the United States, and they found no correlation. However, Rohrer et al. used a purposive sample for their study, which might not have allowed the calculation of an exact value for the association. The reason for the positive association between binge drinking and obesity could be the presence of other impulsive behaviours, e.g., binge eating or abnormal eating patterns, which could confound the association between binge drinking and obesity (18).
4.3. Causes of the conflicting results of the association between alcohol intake and obesity
The aetiology of obesity is considered multifactorial, with several factors contributing to the development of obesity. Not all these factors have been studied or adjusted for when examining the association between alcohol consumption and obesity, and this in turn might bias the estimated relationship between them. The current study controlled for a considerable number of sociodemographic and health-related factors that might confound the relationship between alcohol intake and obesity, with the highest estimated effect sizes for both mean WC and BMI found in males. Type of employment, which was not explored in this study, might function as a potential confounder. Most of the studies on alcohol consumption did not examine individual preferences or cultural influences behind alcohol intake neither examine the type of legislation that might regulate alcohol intake within a country.
Epidemiological studies have examined the association between alcohol consumption and obesity using different instruments. This might also contribute to the conflicting results obtained from different studies. Furthermore, it makes comparisons among studies exceedingly difficult, as no single well-established method was used to measure alcohol consumption. Moreover, the baseline prevalence rates of both alcohol consumption and obesity in a study population can also contribute to inconsistencies in the results obtained when analysing this association. The window period used to recall alcohol intake varied between studies, ranging from a 24-hour recall period (10,19), a 7-day recall period (5, 20), to a 12-month recall period (5). However, a short-term recall period does not account for the usual drinking patterns of individuals, the context under which individuals drink, or the influence of different seasons on alcohol consumption. The current study used a 12-month recall period to examine the association between alcohol consumption and obesity, which is considered more accurate in measurements of the usual consumption trends in individuals.
Types of alcoholic beverages might also affect the life habits of individuals, including eating patterns and physical activity, subsequently affecting body weight. Those who consume beer tend to have worse dietary habits than those who consume other beverages. A US study showed that individuals who drank beer tended to eat fewer fruits, vegetables, and grains than those who consumed wine (21) and were more likely to eat ready-made food (22). Beer consumption was found to be positively associated with smoking, and an interaction of these factors might alter the effect of smoking on body weight. A study showed that current smokers who were heavy drinkers (> 60 grams/day) had a lower BMI than never smokers/former smokers. On the other hand, WC was largest among smokers with heavy lifetime alcohol consumption (23). The current study found that smoking was negatively associated with WC but not BMI after adjustment for sociodemographic and health-related factors. Physical activity is another lifestyle factor that might confound the relationship between alcohol intake and obesity; however, it is difficult to measure.
Most of the studies used a self-report questionnaire to collect data; however, self-report questionnaires are prone to several types of bias (nonresponse bias, recall bias, social desirability bias), and the results may be affected by intentional and unintentional misinterpretations of the questions being asked. Bellis et al. (24) found that self-reported alcohol intake accounted for only 40-60% of total sales. Specifically, heavy drinkers tend to underreport their alcohol intake. The period for recall can also affect the accuracy of self-reported data. However, the data used in the current study were collected during face-to-face interviews conducted by trained staff with the aid of CAPI to minimize errors that might occur during the interview. However, a 12-month recall period can lead to recall bias, which cannot be avoided in studies with such a design.
A limited number of studies have examined the effect of the interaction between genetic factors and environmental factors on obesity. Lio et al., 2016, examined male twins and concluded that alcohol consumption was positively associated with BMI after controlling for sociodemographic and lifestyle factors. However, this association was not observed in the within-pair analysis (25). Edward and colleagues found that in drinkers, alcohol consumption interacted with the presence of a certain allele, (PPARGC1A) rs4619879 (26). Yokoyama et al. found that a specific genotype (alcohol dehydrogenase-1 B) functioned as a strong determinant of body weight among drinkers (27). However, the exact mechanism by which different genes can affect body weight is still not well defined. More research is needed to elucidate the influence of genetic effects on the association between alcohol consumption and obesity.
4.4. Strengths and limitations
This is the first study to examine the association between alcohol consumption and obesity in a nationally representative sample in Ireland. Data collection, including anthropometric measurements, was done by trained personnel, so the chances of question misinterpretation or having missing data are extremely low. The overall response rate for the 2017 Healthy Ireland Survey was significantly high (above 60%), making the data more generalizable to the entire Irish population. Moreover, this study used the AUDIT-C score in the analysis of the association between obesity and alcohol consumption, making the results more generalizable, as the AUDIT-C is a standardized tool to measure harmful alcohol consumption. Last, this study controlled for a variety of sociodemographic and health-related factors that could confound the association between alcohol consumption and obesity.
Nonetheless, there are some limitations to this study. The major limitation is the cross-sectional design, which precludes the inference of a causal relationship between harmful alcohol consumption and obesity. Additionally, this study was prone to recall bias and social desirability bias, which tends to be more prevalent in face-to-face interviews. The study did not look at the type or the quantity of alcohol consumed, nor did it account for other potential confounders like sleep patterns, mental health, or type of occupation as these variables were not collected in the original survey. Moreover, confounders, such as physical activity and diet, were poorly presented in the parent data, which made it difficult to control for them. Furthermore, overweight and obesity were prevalent in nearly two-thirds of the study population, increasing the likelihood of finding an association between alcohol consumption and obesity. The current study did not stratify participants by sex to identify variations in the relationship between harmful alcohol use and obesity between the strata. Furthermore, it did not look at total energy intake; thus, it is not clear if the association is a true association or confounded by unmeasured risk factors. Last underreporting of the amount of alcohol intake is problematic in both self-reporting and face-to-face interviews, especially among heavy drinkers, which might cause significant bias.
4.5. Implications of the study
The results of this study have many implications owing to the high prevalence of both alcohol consumption and obesity in Ireland. Current national and international guidelines for obesity management have not emphasized the possible association between alcohol intake and the risk of obesity development; thus, no recommendation regarding this matter has been made (28, 29). This is partly because of the conflicting evidence of the association between alcohol consumption (both quantity and frequency) and obesity. Nevertheless, these guidelines should highlight the current evidence available and recommendations around the relationship.
Obesity is a public health problem in Ireland, where more than 60% of the population is overweight or obese. Furthermore, the Health Service Executive reported in 2021 that the prevalence of obesity was higher (one in every four people) in the most deprived areas than in the least deprived areas (one in every six people), necessitating more investment in tackling obesity in these disadvantaged communities (28). The management of obesity and overweight in primary healthcare is challenging due to several issues, including a shortage of health services, access to health services, the availability of nutritious food, and the built environment conducive to physical exercise. Additionally, treatment of this condition is highly stigmatized, even among health care workers, and obese patients are commonly subjected to negative judgement. Furthermore, individuals may lack the necessary skills and knowledge to address obesity, rendering them unable to manage their problems. As many determinants, including alcohol consumption, play a role in the development of obesity, treating obesity is considerably difficult and requires a holistic, multilevel, cross-sectoral approach. Ireland established the "Healthy Weight for Ireland: Obesity Policy and Action Plan 2016-2025," which involves various sectors and divides responsibility for obesity prevention among the health and other sectors (transportation, industrial, educational sectors, etc.) (28). However, alcohol intake recommendations were not included in the action plan strategies to combat obesity, due to a lack of definitive evidence of the association between alcohol consumption and obesity. However, it is critical to raise public awareness of the current evidence linking alcohol consumption to obesity, as this may help individuals control their drinking habits. Integrating alcohol consumption recommendations into obesity management action plans is also important at this stage, as it may help standardize the care provided to patients.
Alcohol consumption is a major health issue in Ireland, where more than 80% of the population consumes alcohol. The current study showed that almost half of the participants who completed the AUDIT-C questionnaire were harmful drinkers (scored 5 or more), and over one-third of drinkers engaged in at least one binge drinking occasion per week. Despite current legislation to control alcohol intake, including minimum price units and a ban on advertising alcohol in public areas, the prevalence of harmful alcohol consumption is still high in Ireland. This necessitates a multisectoral approach to tackle the problem and reduce the associated burden. Increasing awareness of psychological as well as physical adverse effects of harmful alcohol consumption is recommended at the population level. It is also important to strengthen the capacity of screening for and treatment of harmful alcohol patterns. Ireland has started a brief advice service through the Making Every Contact Count (MECC) programme that tackles different health-related problems, including obesity and alcohol intake; this service increases awareness of the adverse effects of alcohol dependence on different health factors and provides support for the treatment of harmful alcohol consumption. However, data on the influence of alcohol consumption on obesity are scarce in this programme and thus need to be updated regularly as the evidence evolve. Increasing public awareness about the possible contribution of alcohol consumption, especially harmful alcohol consumption and binge drinking, to obesity is important at this stage. Finally, the information that healthcare professionals convey to patients on this matter needs to be consistent and up to date.
When addressing the association between alcohol consumption and obesity in epidemiological studies, it is important to consider the baseline prevalence of obesity and alcohol consumption in the study population, as this might affect the overall results. The measurement of exposure should be standardized to improve the generalizability and applicability of findings to other population settings. The current study was unique in that it examined the relationship between alcohol consumption and obesity using the AUDIT-C questionnaire, which can reduce inconsistencies in the results obtained. Personal interviews are also preferable to self-report questionnaires because they provide more accurate, complete, and high-quality data. The alcohol intake recall period should be long enough to accurately predict the pattern of alcohol consumption and account for periods where alcohol intake is high. A prospective study design is better for examining temporal sequences and reverse causation than a cross-sectional design, where such relationships cannot be revealed.
Increased spending on research that addresses alcohol consumption and obesity is recommended, especially in Ireland, where both are considered public health issues. This will help deepen the understanding of the exact relationship between alcohol consumption and obesity and further refine the future recommendations regarding alcohol consumption in a population with a high prevalence of obesity. Tailoring advice about alcohol intake according to an individual’s medical background is also recommended. The current recommendations promote moderation in the consumption of alcohol, but further elaboration of an individual’s risk factors is needed.
4.6. Conclusion
This is the first analytical, cross-sectional study to examine the association between alcohol consumption and obesity in an Irish population using Healthy Ireland Survey 2017 data. Harmful alcohol consumption was found to be associated with overweight and obesity (BMI ≥ 25.0 kg/m2) and a larger mean WC after adjustment for sociodemographic and health-related factors. Further controlling for the frequency of alcohol consumption and binge drinking, harmful alcohol consumption was no longer associated with mean WC. Frequent binge drinking was positively and significantly associated with mean WC. Alcohol consumption frequency was not associated with mean WC in this study. Further longitudinal studies are required to explore the causal relationship between alcohol consumption and obesity.