IQ and Level of Alcohol Consumption—Findings from a National Survey of Swedish Conscripts

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Smarter People Tend To Drink More Alcohol

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IQ and Level of Alcohol Consumption—Findings from a National Survey of Swedish Conscripts

Sara Sjölund

Tomas Hemmingsson

Peter Allebeck

First published: 20 February 2015

https://doi.org/10.1111/acer.12656

Citations: 14

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Abstract

Background

Studies of the association between IQ and alcohol consumption have shown conflicting results. The aim of this study was to investigate the association between IQ test results and alcohol consumption, measured as both total alcohol intake and pattern of alcohol use.

Methods

The study population consists of 49,321 Swedish males born 1949 to 1951 who were conscripted for Swedish military service 1969 to 1970. IQ test results were available from tests performed at conscription. Questionnaires performed at conscription provided data on total alcohol intake (consumed grams of alcohol/wk) and pattern of drinking. Multinomial and binomial logistic regressions were performed on the cross‐sectional data to estimate odds ratios (ORs) with 95% confidence intervals (CIs). Adjustments were made for socioeconomic position as a child, psychiatric symptoms and emotional stability, and father's alcohol habits.

Results

We found an increased OR of 1.20 (1.17 to 1.23) for every step decrease on the stanine scale to be a high consumer versus a light consumer of alcohol. For binge drinking, an increased OR of 1.09 (95% CI = 1.08 to 1.11) was estimated for every step decrease on the stanine scale. Adjustment for confounders attenuated the associations. Also, IQ in adolescence was found to be inversely associated with moderate/high alcohol consumption measured in middle age.

Conclusions

We found that lower results on IQ tests are associated with higher consumption of alcohol measured in terms of both total alcohol intake and binge drinking in Swedish adolescent men.

Intelligence has been shown to be associated with various health‐related outcomes in several studies (Andersson et al., 2008; Calvin et al., 2011; David et al., 1997; Gale et al., 2010; Hart et al., 2004; Hemmingsson et al., 2007; Martin et al., 2004). However, previous findings on cognitive ability and alcohol‐related problems have not been consistent, possibly due to differences between the outcomes assessed.

One suggested explanation for the association between intelligence and health is that cognitive skills enhance possibilities to make healthy lifestyle choices. Cognitive ability has been found to be associated with several health‐related behaviors, such as smoking, food intake, and physical activity (Batty et al., 2007b,c; Hemmingsson et al., 2008). The scientific literature on intelligence and alcohol consumption in adolescence, measured as total intake and type of drinking, is scarce. A twin study from the United States showed that a high IQ assessed at age 17 was associated with heavier alcohol use as measured by an alcohol use composite, taking into account symptoms of alcohol abuse/dependence, number of intoxications, frequency of use and number of drinks during a year, and maximum number of drinks within 24 hours (Johnson et al., 2009). A study from Switzerland investigated how IQ test results from conscription were associated with frequency of drinking, defined as nondrinking, rare drinking (1 to 5 times/y), occasional drinking (1 to 5 times/month), moderate drinking (1 to 5 times/wk), and daily drinking. It showed that high performance on IQ tests had a positive association with moderate drinking (Muller et al., 2013). In the 1970 British Cohort Study, it was found that higher childhood mental ability was associated with higher alcohol intake as an adult (Batty et al., 2008). Another study from the United States, of a population 14 to 21 years of age, showed, on a measure of verbal intelligence, that lower verbal intelligence was associated with lower alcohol consumption, but also with a higher risk of alcohol‐related problems among those who consumed alcohol (Windle and Blane, 1989).

Intelligence is commonly defined as “a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience” (Gottfredson, 1997). There are several tests of intelligence available, and the main difference between them lies in the recognition, or not, of a general factor, “g,” as introduced by Spearman. The “g” factor theory addresses the positive correlations found between tests designed to capture different suggested areas of intelligence, for example, verbal, logical, and spatial. Instead of 1 “g” factor, Horn and Cattell suggested 5 “general” factors, of which those concerned with “fluid” and “crystallized” abilities are the most influential. The first is a matter of basic ability to reason (g_f), while the latter (g_c) concerns how well the individual has invested his/her fluid ability in society to gain knowledge of value. These 2 theories are often contrasted with that of Thurstone, in whose model primary mental abilities are expected to explain test results more independently (Carlstedt, 2000; Gustafsson, 1984; Nisbett et al., 2012). However, as concluded by Deary (2012), there are few empirical grounds for considering intelligence without the “g”‐factor.

Studies on alcohol consumption should consider both total alcohol intake and pattern of drinking (Rehm et al., 2003). Although few studies have been performed on patterns of drinking, they have been shown to be of importance for certain diagnoses, for example, ischemic heart disease, fetal alcohol syndrome, and injury (Plunk et al., 2014; Rehm et al., 2010). There are different definitions of patterns of drinking in the literature. Normally, binge drinking is contrasted with a moderate or steady type of drinking, but there is a lack of distinct and broadly acknowledged measures of the different patterns of consumption (Field et al., 2008). It is, however, known, that binge drinking is more common among young adults and adolescents (Kuntsche et al., 2004). Further, a systematic review by McCambridge and colleagues (2011) showed that high alcohol consumption in late adolescence is carried into adulthood and as too are the problems associated with alcohol.

The aim of this study was to examine the association between intelligence and total alcohol intake during a specific time period and pattern of drinking. We have, in an earlier study, shown an inverse association between the results of IQ tests in adolescence and alcohol‐related disease and death in adulthood (Sjolund et al., 2012). We therefore hypothesize that IQ test results have inverse associations with the 2 measures of alcohol consumption.

Our specific research questions were as follows:

1. Is there an association between intelligence and total alcohol intake in adolescence?
2. Is there an association between intelligence and pattern of drinking in adolescence?
3. Are there differences in the associations between different the cognitive factors measured in an IQ test and total alcohol intake and pattern of drinking in adolescence?
4. Does any association between IQ test results and total alcohol intake in adolescence persist into adulthood?