Lifetime and twelve-month prevalence of heavy-drinking in Singapore: Results from a representative cross-sectional study

Adverse effects of over-consumption of alcohol are well-documented, and two forms of alcohol use disorder- alcohol abuse and alcohol dependence, are classified in the Diagnostic and Statistical Manual of Mental Disorders, 4^th edition (DSM-IV) of the American Psychiatric Association. However, some patterns of alcohol consumption may be harmful even in the absence of alcohol abuse or dependence, and binge drinking is recognised as a potential cause of morbidity and mortality [1–7].

Binge drinking refers to high volume alcohol consumption over a short period of time, and is frequently defined as the consumption of four or more drinks at a single sitting for women, and of five or more drinks at a single sitting for men [8]. Binge drinking is associated with physiological effects such as behavioural disinhibition, temporary impairment of judgment, nausea and vomiting, and hangover symptoms. Studies have linked binge drinking to increased coronary heart disease risk [1], psychiatric morbidity [2], and cognitive impairment [3]. Children born to women who binge drink during the pregnancy appear to have a higher risk of psychiatric and behavioural difficulties [4]. In addition, binge drinking is also associated with a myriad of social issues–and is associated with risky sexual behavior [5, 6], violence [5], and injuries resulting from motor and other accidents [5, 7]. Overall, binge drinking is relatively prevalent; data from representative samples in the US suggest a 30-day period prevalence of 17.1% [9], while data from Brazil suggest that 26.7% had at least 1 episode of binge-drinking in the past year [10].

Singapore is an island city-state in South-East Asia, with a multi-ethnic population of about 5 million, with 3.77 million Singapore citizens and Permanent Resident [11]. The resident population comprises Chinese (74.1%), Malays (13.4%), Indians (9.2%) and Other ethnic groups (3.3%) (11). We recently showed that the prevalence of alcohol use disorders as established using DSM-IV was relatively low in Singapore, with a lifetime prevalence of alcohol abuse and alcohol dependence of 3.1 and 0.5% respectively [12]. We had also earlier noted an increase in past-month binge drinking rates in the Singapore resident population, from an age-adjusted prevalence of 5.1% in 1992 to 10% in 2004 [13], based on data obtained from the National Health Surveys, which were representatively-sampled serial cross-sectional surveys conducted in Singapore with a 6-yearly interval. The definition of binge drinking was operationalised as consuming 5 drinks or more in a single drinking session for both men and women. The data available suggest that while diagnoses of alcohol use disorders were low, harmful patterns of alcohol drinking may be relatively common in Singapore.

In this paper, we examine the prevalence of heavy drinking (as a proxy for binge drinking) using data from a nationally representative cross-sectional survey. We also evaluated correlations between heavy drinking and socio-demographic factors and the concomitant presence of self-reported physical conditions and psychiatric conditions (based on DSM-IV criteria). Finally, we assessed the impact of heavy drinking by evaluating differences in self-reported quality of life and days of work-loss.

From an initial study frame of 13,500 individuals, 9116 (67.5%) were identified, and of these, 6648 (72.9%) were successfully interviewed. 854 (9.4%) refused to participate, 664 (7.3%) were either not contactable or were deceased, 554 (6.1%) had moved to another location or country, and 396 (4.3%) were ineligible due to language barrier or inability to complete the interview. Subsequently, 32 completed interviews were voided during the quality review, leaving a total study population of 6616 individuals. The overall response rate for the study, excluding the ineligible 396 cases, was 75.9% (n = 6616).

The prevalence of heavy drinking differed significantly by socio-demographic variables. Men were more likely to drink heavily than women. Younger participants were more likely to drink heavily than older ones. Malays were less likely to drink heavily than the other ethnic groups, while those with an ethnicity of “Others” were more likely to drink heavily. Married and widowed individuals were less likely to drink heavily than single individuals. People with higher incomes were more likely to drink heavily. People of higher education status were more likely to drink heavily, while economically inactive people were less likely to drink heavily (Table 1).

After adjusting for socio-demographic factors, women were less likely to drink heavily than men (OR 0.37, 95% CI 0.29-0.48 for 12-month and OR 0.32, 95% CI 0.25-0.40 for lifetime prevalence), and Malays were less likely to drink heavily than Chinese (OR 0.21, 95% CI 0.16-0.28 for 12-month and OR 0.27, 95% CI 0.22-0.34 for lifetime prevalence), while those with an “Others” ethnicity were more likely to drink heavily (OR 7.20, 95% CI 4.93-10.51 for 12-month and OR 7.29, 95% CI 5.00-10.67 for lifetime prevalence). Older people were much less likely to drink heavily (OR 0.19, 95% CI 0.07-0.50 for 12-month and OR 0.20, 95% CI 0.09-0.42 for lifetime prevalence of heavy drinking in those 65 years and above, compared to those 18–34 years), while participants with high personal income were more likely to drink heavily (OR 1.67, 95% CI 1.08-2.57 for 12-month and OR 1.75, 95% CI 1.19-2.58 for lifetime prevalence in those earning S$50 000 and more annually, compared to those earning less than S$20 000 annually). Divorced or separated individuals were more likely to report lifetime heavy drinking compared to single persons (OR 1.88, 95% CI 1.12-3.16), although the increased OR for 12-month heavy drinking was not significant. Married persons were less likely to report 12-month heavy drinking (OR 0.63, 95% CI 0.47-0.84), although the decreased OR was not significant for lifetime heavy drinking (Table 1).

Overall, no differences in quality of life as measured on the index derived from the EuroQoL 5D were seen among lifetime heavy drinkers who did not have alcohol use disorder compared to non- heavy drinkers, although lifetime heavy drinkers with alcohol use disorder had a significantly lower score as compared to non-heavy drinkers. No differences were seen with 12-month heavy drinkers, with or without alcohol use disorder, compared to non- heavy drinkers. When stratified by age-group, lifetime and twelve-month heavy drinkers with alcohol use disorder in the 18–34 year age group reported significantly lower quality of life compared to non- heavy drinkers (p = 0.0003, 0.0419 respectively). Twelve-month heavy drinkers without alcohol use disorder aged 50–64 reported higher quality of life than older non- heavy drinkers in the 50–64 year age group, (p = 0.0078) (Table 4).

Lifetime heavy drinkers with alcohol use disorder and without alcohol use disorder reported poorer quality of life compared to non- heavy drinkers without alcohol use disorder (p < 0.0001 and 0.019, respectively) on the VAS. Among 12-month heavy -drinkers, significantly lower quality of life was reported only among those with alcohol use disorder (p = <0.0001). Lifetime and 12-month heavy drinkers with alcohol use disorder reported significantly lower quality of life in both the 18–34 year (p < 0.0001 and 0.0158 respectively) and the 35–49 year (p < 0.0001 and 0.037 respectively) age groups. No significant difference in quality of life was reported by lifetime and 12 month heavy drinkers without alcohol use disorder, except for lifetime heavy drinkers in the 35–49 year age group, which reported a significantly lower quality of life (p = 0.0315). No clear differences in self-reported loss in work days were seen, with or without stratification by age, except for 12 month heavy drinkers without alcohol use disorder in the 50–64 year age group, where they reported fewer days lost (p = 0.022) (Table 4).

In this study of a representative population of adult Singaporeans and Singapore permanent residents, we found that 12.6% of all adult Singapore residents reported heavy drinking in the past 12 months, and 15.9% reported lifetime heavy-drinking. There were strong socio-demographic differences between heavy-drinkers and non-drinkers, with heavy-drinkers being more likely to be men, younger, single, and earning higher income. Malays were much less likely to be heavy drinkers compared to the Chinese. Heavy drinking was positively associated with major depression, the presence of any mood disorder, and chronic pain. It was also strongly associated with alcohol dependence and alcohol abuse, and nicotine dependence. Overall, heavy drinkers reported lower quality of life compared to non- heavy drinkers on the EuroQoL indexed score and Visual Analogue Scale.

Data from the National Health Survey in 2004 previously suggested a binge-drinking prevalence of about 10% [13]. Our results of 12.6% for heavy drinking are consistent with the data obtained from 2004. Additionally, both studies identified the young, males, and people with higher incomes as being more likely to drink heavily, while Malays were less likely to do so [13]. The strong ethnic differences in heavy-drinking rates are likely to be due to the role of culture and religion as a protective factor. Malays in Singapore are almost all Muslims, for whom there is a religious prohibition on alcohol consumption. Further analyses of our data show that the proportion of heavy drinkers (both over twelve months or lifetime) in Malays who drink was similar to or higher than the proportion in Chinese who drink (not shown in tables), in contrast to the overall prevalence of heavy drinking, which is much lower among Malays. This suggests that the effect of ethnicity on heavy drinking works via reducing initiation of drinking rather than drinking volume. This is consistent with the hypothesis that the protective effect of ethnicity on heavy drinking is mediated through religion, since Islam prohibits alcohol consumption. We also note a very high prevalence of alcohol consumption among people of “Others” ethnicities, with an odds of heavy drinking of about 7 times higher than the Chinese. This increase is statistically significant. In Singapore, the majority of people classified as “Others” are people of Eurasian or Caucasian origins, although other ethnicities such as Thai, or Japanese are also classified in this group. Further research is needed to evaluate which ethnicities within this group are drinking more, and to understand the context of the heavy alcohol consumption, so that appropriate intervention programmes can be designed and implemented.

The prevalence of heavy drinking is much lower than those reported in non-Asian countries [9, 10]. Heavy drinking in Singapore is primarily a condition of the young, as has been reported in other studies [9, 10]. Our findings with regard to income and marital status are consistent with findings reported previously [9, 10, 19]. We did not detect an inverse association with education, which has been reported elsewhere [19].

Alcohol use in Singapore in the past was much lower compared to Western and some Asian countries, with low rates seen particularly amongst Malays and women [13]. However, both published studies and anecdotal evidence suggest that alcohol use is becoming accepted as a social norm in Singapore [13]. Alcohol use disorder has increased in recent years, especially among the young [12]. Alcohol use and abuse control policies in Singapore depend on a variety of measures, including heavy taxation on alcohol products [20], legislation such as restrictions on sale of alcohol to minors and anti-drink-driving laws, and promotional campaigns to curb misuse of alcohol by the Health Promotion Board and the Traffic Police [21].

We found an association of heavy drinking with mental illnesses, in particular major depression, also consistent with findings from other studies [2, 22, 23]. The strong association with alcohol abuse and use is not unexpected. However, the vast majority of heavy drinkers do not have alcohol use disorders, and alcohol use disorders do not adequately predict heavy drinking. The association of heavy drinking with depression, and to a lesser extent, with anxiety disorders, is consistent with the higher prevalence of unhealthy lifestyle behaviour (including poorer diet, lower levels of physical activity, higher smoking prevalence) that has been reported among people with psychiatric disorders [24, 25]. Heavy drinking was also positively and strongly associated with nicotine dependence, again consistent with results from other studies [26]. In our data, more than a quarter of people who fulfilled criteria for major depressive disorder reported heavy drinking in the last 12 months. This suggests that doctors managing patients with depression may need to assess for and manage unsafe alcohol use in their patients even in the absence of alcohol abuse or alcohol dependence. There is some evidence that reducing alcohol consumption might improve depressive symptoms [2].

We note a significant positive association between chronic pain and lifetime heavy drinking, and a borderline significant finding with twelve-month heavy drinking. Further, heavy drinkers with or without alcohol use disorder reported poorer scores on the pain/discomfort dimension on the EuroQoL 5D compared to non-heavy drinkers. A possible explanation for this association is that this relationship could be mediated through mental disorders such as major depression: we observe a positive association between heavy drinking and depression in this paper, and previous analyses of our dataset have shown that the prevalence of mental disorders including depression is higher among those with chronic pain [27]. Another explanation for these associations may be that the higher prevalence reflects attempts by persons living with depression or chronic pain to alleviate their symptoms through the use of alcohol.

Our results show that the greatest declines to quality of life and to work-day loss relate to the presence of mental illnesses, and do not suggest that heavy drinking in the absence of alcohol use disorder is associated with significant loss of quality of life, nor with loss in work-days. Other studies have reported changes in quality of life associated with binge drinking [28, 29], and a recent study in Norway has suggested that binge drinking is associated with absenteeism in the workforce [30]. This discrepancy could be due to a ceiling effect in the instruments used [31], with a relative lack of discrimination among otherwise well individuals. We did detect differences in quality of life among younger participants who drank heavily, compared to those who did not, on the VAS but not using the index score. These results are consistent with findings from other countries (28,29), and suggest that for younger, otherwise healthy populations, the VAS may be more discriminatory than the index scores.

In the older age-groups, higher quality of life was unexpectedly reported among heavy drinkers without alcohol use disorder compared to non-heavy drinkers. This may reflect reverse causation where healthy individuals are more likely than persons with physical illnesses to continue drinking, or it may be that there is no decline in quality of life associated with heavy drinking for the majority of drinkers, who may find the social interaction associated with drinking a strong promoter of emotional well-being. Interestingly, a recent study in the US also reported that heavy drinkers had higher measures of positive health in some domains [32].

There are several limitations in our study. We used a cross-sectional design, and while our data give nationally representative figures, we were unable to establish the causality of associations that we have found. Our contact rate of 67.5% and response rate of 75.9% are reasonable and consistent with response rates obtained in population-based surveys conducted elsewhere. However, contact and response rates of heavy drinkers may differ from non-heavy drinkers, and this differential response rate may bias our prevalence estimates. A priori, we assume that heavy drinkers are likely to have lower contact and response rates. If so, our prevalence estimates would represent a lower limit, and the true prevalence may be higher than estimated.

We used an operational definition of heavy drinking as a consumption of 4 or 5 drinks (depending on gender) in a single day, in contrast to the traditional binge drinking definition of 4 or 5 units over a single drinking episode. Our results therefore does not measure 12-month binge drinking rates, and direct comparisons with binge drinking rates cited in other studies are not possible. Because binge drinkers are heavy drinkers, but heavy drinkers need not be binge drinkers, our prevalence estimate may be an overestimate of the 12-month binge drinking rate, and serve as an upper estimate of the true binge drinking rate. The definition for 12- month heavy drinking (largest number of drinks in a single day) was different from lifetime heavy drinking (usual number of drinks). The lifetime heavy drinking estimate will underestimate the true prevalence of lifetime binge drinking. We believe 12-month heavy drinking is a better proxy for binge drinking than the lifetime one.

Finally, we used face-to-face interviews for this study. Participants may not have reported accurate consumption rates because of their perceptions of the social acceptability of alcohol consumption. This may be so especially amongst females or Malays, where societal expectations are that they do not drink. Conversely, young males may have over-reported their consumption patterns. We have tried to reduce this misclassification bias by training our interviewers to administer the interviews in a sensitive and neutral manner, and using standard questionnaires.

In summary, despite low reported rates of alcohol abuse and alcohol dependence, we find a relatively high prevalence of 12-month heavy drinking of 12.6%, and lifetime heavy drinking of 15.9%. Although these rates are lower compared to other countries, it is important to continue to monitor alcohol consumption trends. Efforts to improve awareness among the young of the ill effects of heavy drinking, and to mitigate harms associated with heavy drinking and intoxication also need to be continued.