Significance We find that alcohol intolerance, which occurs randomly and leads affected people systematically to resist the impulse to consume alcohol, enables improved impulse control in another behavioral domain. Our findings show that impulse control can develop in adult populations as a result of exercising routine behaviors in naturally occurring environments. This finding is important because the ability to control tempting impulses significantly impacts the health and well-being of people at all ages. Our findings complement theory by providing rigorous empirical evidence that simple lifestyle changes may have significant personal well-being benefits. In particular, small acts of self-control, such as resisting drinking or always waking at the same time, can increase one’s overall ability to resist selfish temptations.

Abstract The ability to control tempting impulses impacts health, education, and general socioeconomic outcomes among people at all ages. Consequently, whether and how impulse control develops in adult populations is a topic of enduring interest. Although past research has shed important light on this question using controlled intervention studies, here we take advantage of a natural experiment in China, where males but not females encounter substantial social pressure to consume alcohol. One-third of our sample, all of whom are Han Chinese, is intolerant to alcohol, whereas the remaining control sample is observationally identical but alcohol tolerant. Consistent with previous literature, we find that intolerant males are significantly more likely to exercise willpower to limit their alcohol consumption than alcohol-tolerant males. In view of the strength model of self-control, we hypothesize that this enables improved impulse control in other contexts as well. To investigate this hypothesis, we compare decisions in laboratory games of self-control between the tolerant and intolerant groups. We find that males intolerant to alcohol and who regularly encounter drinking environments control their selfish impulses significantly better than their tolerant counterparts. On the other hand, we find that female Han Chinese intolerant to alcohol do not use self-control to limit alcohol consumption more than tolerant females, nor do the tolerant and intolerant females exhibit differences in self-control behaviors. Our research indicates that impulse control can be developed in adult populations as a result of self-control behaviors in natural environments, and shows that this skill has generalizable benefits across behavioral domains.

Humans are often tempted to pursue an immediate benefit, even when they know it may result in substantial long-run cost. Controlling these tempting impulses requires willpower (1). Impulse control is important to a large number of social and economic environments, including health behavior (2) and weight loss (through both food control and exercise) (3), violence and crime (4), and spending and saving in household finances (5). A long multidisciplinary empirical and theoretical literature discusses the role of impulse control in social and economic decision making (6, 7).

The question of whether impulse control can be acquired or improved has been long studied, both empirically (8⇓–10) and theoretically. An important contribution to this literature is the so-called “strength model” of self-control (see, for example, refs. 11⇓–13), which argues self-control is like a “muscle” that can be depleted by short-term exertion, and yet that the same exertion can lead to it strengthening. [Although we focus on the strength model, alternative models of self-control have been suggested (14, 15).] The model predicts that practicing self-control on specific tasks increases one’s ability to exercise self-control broadly across multiple domains (16). This prediction has been frequently tested using designed experimental interventions (17, 18). To our knowledge, however, there have been no tests of the strength model based on “natural experiments,” where exogenous population variation leads to systematic differences in the need to practice small acts of self-control. This paper fills that gap.

Our interest is to investigate a key prediction of the strength model: repeatedly practicing small acts of self-control leaves a person more able to use willpower than another observationally identical person without this practice. Many experimental tests of this prediction have appeared (17, 18). A typical experiment assigns people randomly to practice self-control (or not) for a relatively short period (usually days or weeks), and subsequently assesses their ability to use self-control in a laboratory task. The meta-analysis of Hagger et al. (17) reveals that the strength model is generally supported by the literature, and in particular the ability to practice self-control does seem to increase as a result of practice. [Others who have analyzed these data using different approaches reach different conclusions (19).] Baumeister and Vohs (18) further argue that, “exercising self-regulation of one or two sorts of behaviors causes discernible improvements on seemingly unrelated tasks.” At the same time, as noted by Muraven (20), this literature suffers from confounds that create difficulties in tracing the source of this effect to an increase in the effective stock of willpower.

For example, one reason a person’s self-control might improve after an intervention is because they become more aware of the importance of self-control. In the same way that raising the salience of a norm tends to improve obedience to that norm (21), emphasizing the importance of self-control by asking people to practice self-control may leave them more likely to comply with tasks that require self-control. Muraven (20) suggests that another confound is that a person, focused on and thus realizing they are able to practice self-control, may gain additional confidence in this ability. This increased confidence may affect their ability to exercise self-control in a subsequent task, particularly one in which their performance is being monitored.

We study impulse control among adult Han Chinese displaying intolerance to alcohol, in comparison with a control group of adult Han Chinese without this intolerance. We provide evidence that male Han Chinese with alcohol intolerance practice small acts of self-control over alcohol more regularly than males in our tolerant groups. We argue this is the only systematic difference in the exercise of self-control between the tolerant and intolerant groups. Consequently, the alcohol-intolerant male sample would be expected, by the strength model, to be better able to control tempting impulses. Note that our approach has the advantage that confounds, such as salience and confidence-building, are absent.

Our sample (48.6% female) is drawn from the Han Chinese undergraduate population at a leading Chinese university. Members of our sample are similar in age and background: homogeneity of the participant pool is the reason we use this population. We are aware of no evidence that alcohol intolerance is associated with personality or preferences, and in our sample we find no evidence that this polymorphism systematically predicts personality type, attitudes toward risk, or prosociality. Other than alcohol intolerance and gender, both of which are expected to impact systematically use of self-control, we are aware of no other reason or evidence that practice of self-control would differ systematically among this population.

Alcohol intolerance arises because of the presence of the ALDH2 Lys487 allele (see SI Appendix for details). Since there is an equal chance that either parental allele will be passed on to offspring, alcohol intolerance can be understood as occurring randomly in the population (22). This randomization across our sample is crucial for the causal inferences we report below. Note that our research strategy connects to the Mendelian randomization literature (23⇓⇓–26), which also takes advantage of natural experiments implied by random assignments of genes from parents to offspring.

It is important to note that exposure to drinking environments is also randomized across our sample: we find no evidence that any variable we measure differs systematically among males who are more or less frequently exposed to environments that include alcohol, and the frequency of exposure to drinking environments is statistically identical between the tolerant and intolerant groups. (We find that females measure higher on extroversion more frequently in drinking environments, but no other trait differences between those regularly and rarely in environments that include alcohol.) A key reason is that participants are randomly assigned to dorm rooms, and the frequency of exposure to alcohol has been shown to be dependent on peers and the social pressure they exercise (27⇓–29). [Many have taken advantage of random dorm assignment to study peer effects. Early examples are Sacerdote (30), Zimmerman (31), Stinebrickner and Stinebrickner (32), and Boisjoly et al. (33). More recently, Jain and Kapoor (34) and Shue (35) used random dorm assignment to study peer effects on attitudes and behavior, as well as academic and career outcomes.]

China does not have a legal drinking age, and college-aged Chinese males experience substantial social pressure to drink to promote business and social relationships. Despite its immediate relational benefits, previous research finds that alcohol-intolerant males use self-control more than their alcohol-tolerant counterparts to limit their drinking (36). In contrast, females face little social pressure to drink in China and, moreover, generally consume very little alcohol. Consequently, we do not expect alcohol intolerance to modulate Chinese females’ use of self-control in drinking environments.

We find alcohol-intolerant males in our sample are significantly more likely to use self-control to limit their alcohol consumption in drinking environments than tolerant males. Moreover, consistent with the strength model, we find that males regularly exposed to drinking environments and who exhibit alcohol intolerance display greater self-control over selfish cheating behavior than their tolerant counterparts. Furthermore, females do not exhibit differences between tolerant and intolerant groups in either propensity to use self-control in drinking environments or in decisions to cheat.

These results are consistent with the view that impulse control, like a muscle, can be developed in natural environments as a consequence of practicing small acts of self-control, and that this has generalizable benefits across multiple behavioral domains (16, 18, 20). It is worth emphasizing that, whereas substantial experimental research based on designed interventions has provided support for the strength model (e.g., refs. 13 and 37⇓–39), to our knowledge ours is unique in discovering the positive spillover effects associated with practicing self-control in a naturally occurring context.

Literature Review Acquired Impulse Control. Impulse control can be acquired through practice. Ainslie (8) used pigeons to study the possibility that animals can learn self-control, finding that some subjects could learn to control their behavior for a delayed reward. An early survey of learned self-control is found in Ainslie (9). Among humans, self-control is usually developed during childhood (4). There is evidence, however, indicating self-control can also be strengthened among adolescents and adults. Muraven et al. (40) studied college students who spent 2 wk performing one of three self-control exercises (improving posture, regulating moods, and maintaining a diary of eating). Compared with a no-exercise control group, these participants showed significant improvements in their self-control, as demonstrated by their ability to squeeze a handgrip for a longer time. The strength model of self-control of Muraven and Baumeister (20) argues that self-control, like a muscle, can be strengthened through practice. Substantial empirical support for the strength model has appeared in the literature. For example, Muraven (20) reported data from 92 adult participants engaged in a “stop signal” task to measure their self-control. The participants found that after 2 wk of practicing self-control by, for example, avoiding sweets or squeezing a handgrip, participants’ self-control performance improved significantly. Furthermore, Muraven (41) found that practicing self-control helped one to quit smoking. Other examples have been found in the practice of physical exercise (42), academic study (43), and financial monitoring (44). To our knowledge, all previous tests of the strength model have been based on designed interventions. Our paper is unique in that our investigation takes advantage of naturally occurring variation in the frequency with which people practice self-control. Assessing Self-Control Using Laboratory Cheating Games. Self-control in the laboratory is frequently studied through the use of cheating games. Cheating is a socially costly behavior and has been studied heavily in economics. Early cheap-talk games explored humans’ cheating behavior, where the subjects could choose cheating strategies to increase their own payoff and decrease their opponents’ payoff (45, 46). Later studies used self-reported payoffs, so that the experimenter could not detect individual participant’s cheating behavior (47⇓–49). Prior research has established a clear causal relationship between willpower and cheating decisions. For example, Mead et al. (50) studied the relation between self-control and cheating for selfish gain. The authors found that participants with depleted self-control misrepresented their performance for monetary gain to a greater extent than did nondepleted participants. The implication is that cheating for profit increases when people’s capacity to exert self-control is impaired. Gino et al. (51) found similarly that depletion of self-control leads to heightened cheating because of a reduced attention to moral standards (see also ref. 47). In addition, Barnes et al. (52) found that people who consumed self-control resources (in their case, by having too little sleep) were more likely to choose to cheat.

Hypotheses The above discussion motivates the following three related hypotheses we tested using our Han Chinese sample. Detailed explanation of these hypotheses is found in SI Appendix. Hypothesis 1. Males with alcohol intolerance practice self-control in drinking environments more than tolerant males. Female self-control over drinking alcohol is not modulated by alcohol intolerance. Hypothesis 2. Males intolerant to alcohol and regularly in drinking environments will develop generalized improvement in self-control in relation to otherwise identical tolerant males and intolerant males not regularly exposed to drinking environments. In particular, in relation to alcohol-tolerant males and -intolerant males not regularly exposed to drinking environments, intolerant males regularly in drinking environments will demonstrate an improved ability to use willpower to resist selfish temptations. Hypothesis 3. Female self-control will be modulated by neither alcohol intolerance nor exposure to drinking environments.

Experiment Design We measure self-control using a simple game where participants must control a selfish impulse to cheat for monetary gain. [Mead et al. (50) and Gino et al. (51), among others, report data showing that people with low self-control are more likely to misreport their performance to achieve monetary gain. Further discussion of the relation between willpower and behavior in cheating games is found in Assessing Self-Control Using Laboratory Cheating Games, above.] We used this game because it is easy for participants to understand, rapidly conducted, and a reliable as a measure of self-control (50, 51). Following Fischbacher and Heusi (49), each participant was individually given a six-sided die. Participants were told that they could roll the die as many times as they wished to verify it worked properly. However, only the first roll, which they were told to remember during the rolling process, would decide their payoff. All die rolls were private: only the participant knew the outcome of their first die-roll. The payoff structure is described in Table 1, and all participants were aware of this payoff structure when reporting to the experimenter the outcome of their first die-roll. Table 1. Payoffs in the self-control game As in the literature cited above, because participants’ die-rolls were private, we are not able to detect cheating at the individual level. We draw inferences regarding cheating from the overall outcome distribution. If nobody cheats, each number should be reported at a rate that does not statistically differ from a one-in-six frequency. If people systematically cheat to gain a higher payoff, then we would expect outcomes three, four, or five to be reported at statistically greater than a one-in-six frequency. We began each session by conducting four decision tasks. The first three were: the self-control (cheating) game, a risk-attitude elicitation, and an elicitation for prosociality. The fourth task was either a time-preference elicitation or a task that measured ambiguity aversion. The length of our experiment precluded running all preference elicitations in all sessions. We decided risk-attitudes and prosociality were important to be able to measure as accurately as possible, and so included them in all sessions. We measured time preference in most sessions (nearly 90%) and otherwise measured ambiguity aversion. In all cases, we found no differences between tolerant and intolerant groups. The sequence of the four tasks was randomly determined in each session. Our goal with these initial decision tasks was to obtain evidence on whether attitudes toward risk or ambiguity, prosociality, or time-preference might systematically vary between tolerant and intolerant groups. If so, this evidence might suggest alternative explanations for any differences discovered in cheating behavior. As shown below, however, we found no such evidence and thus did not pursue this issue further. Detailed instructions for each of these tasks are provided in SI Appendix. In brief, to elicit prosociality, participants made decisions as Sender in a 20 Renminbi (RMB) dictator game (53, 54). Our risk preference elicitation was based on a 30 RMB risky investment game (55, 56). Time preferences were elicited by asking subjects to decide between two future payments: smaller sooner or larger later (57). Ambiguity aversion was elicited using the task of Ellsberg (58), which involves drawing a ball from an urn with either known or ambiguous color distribution. Following these decision tasks, we administered an ethanol patch test to detect alcohol intolerance (Materials and Methods) and distributed a questionnaire regarding alcohol consumption and tolerance, as well as other allergies and gambling behaviors. Participants also completed a demographic and personality survey. The survey included questions about age, gender, and grade. The survey also included several personality scales: Big Five (59), Machiavelli (60), Self-Monitoring (61), Rosenberg's Self-Esteem (62), and Consideration of Future Consequences (63) (see SI Appendix for details).

Discussion We studied self-control among a population intolerant to alcohol, in comparison with an observationally identical but alcohol-tolerant control group. Our data support the strength model of self-control. We find that alcohol-intolerant males who regularly encounter drinking environments are significantly better able to exercise self-control in cheating games than alcohol-tolerant males or -intolerant males less frequently exposed to drinking environments. The reason is that alcohol-intolerant males exercise more self-control than tolerant males to resist the impulse to drink, and this regular practice improves intolerant males’ ability to control their selfish impulses. Furthermore, we find that females behave statistically identically in cheating games regardless of their exposure to drinking environments and regardless of whether they are intolerant to alcohol. We argued the reason is that alcohol-intolerant females do not exercise self-control in drinking environments differently than do alcohol-tolerant females, and thus this result is also consistent with the strength model. Although we did not observe differences in preferences or personality between tolerant and intolerant males, this might be in part because of the narrow range of ages in our sample. Systematic differences in the practice of self-control could lead to such differences emerging over time. It would be profitable for future research to investigate whether, when, and which trait differences emerge, and how these impact social and economic outcomes. Self-control is an important component of social and economic environments. Our research is unique in that it shows that an adult’s ability to manage selfish impulses improves as a consequence of using self-control in naturally occurring environments. An implication is that small and simple day-to-day lifestyle changes can have significant personal health and well-being benefits. In particular, in view of our findings, one might speculate that regular acts of self-control, such as resisting drinking or perhaps routinely exercising or waking at the same time each day, might improve one’s overall ability to resist selfish temptations.

Materials and Methods Human Subjects Protections. This study was reviewed and approved by George Mason University’s Human Subjects Internal Review Board, protocol no. 575329–1. Informed consent was obtained from participants at the beginning of each session. Detecting Alcohol Intolerance. Following the die-roll game, we tested each subject for alcohol intolerance using a procedure detailed by Muramatsu et al. (67). Specifically, 0.1 mL of 70% (by volume) ethanol was pipetted onto a 15 × 15-mm lint pad affixed to an adhesive tape. The same volume of distilled water was pipetted onto an identical pad and used as a control. Both patches were attached to the inner surface of each participant’s upper arm for 7 min and then removed. A patch area that was judged to show erythema 10–15 min after removal to a greater degree than the distilled water baseline indicated intolerance to alcohol (68). Procedures. Experiments were conducted in the laboratory of the Business School in Central South University. We initially collected 226 observations followed by a second set of sessions resulting in 254 additional observations. We conducted 22 sessions in total. Recruiting was done by posting flyers around campus. Subjects were undergraduate students at Central South University, all of whom were from the Han ethnic group and at least 18 y old. We paid the participants with cash, in private, and immediately after the experiments (with the exception of the delayed payoffs from the time preferences task, which was paid on the corresponding payment date). Each participant received 5 Yuan for participating, and the average payoff was 82 RMB. The four decision tasks were implemented using paper and pencil. Instructions for each task were put into envelopes and distributed. Participants wrote their experiment ID on the instructions. Participants returned the instructions to the envelope after decisions were made, and the experimenter collected the envelopes. Each session lasted about 2 h. After the experiment participants completed a short questionnaire about behaviors related to alcohol. If the survey was not completed while in the laboratory, we followed-up via text-message.

Acknowledgments We thank the editor and two anonymous reviewers for many insightful comments that improved this paper. Funding for this research was provided by the National Natural Science Foundation of China (Grants 71501193, 71372063, and 71631008).

Footnotes Author contributions: J.W., Y.R., and D.E.H. designed research; J.W. performed research; J.W. and D.E.H. analyzed data; and J.W., Y.R., and D.E.H. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission. R.B. is a Guest Editor invited by the Editorial Board.

↵*One can compute a Bonferroni correction for P values assuming 15 comparisons, showing that to achieve significance at the 5% level, one requires an uncorrected P < 0.004. Accordingly, we find no significant differences among males, and females differ only in that those with regular exposure to drinking environments measure higher in extraversion.

↵ † Our analysis is based on aggregating the three higher (high payoff) and three lower (low payoff) numbers. The reason is that our design does not allow us to detect how people cheat at the individual level. Aggregating provides a statistically powerful approach to detect cheating while remaining agnostic about how cheating occurs. SI Appendix, Tables S6 and S7 detail results of analyses at different levels of aggregation. The results are qualitatively unchanged.

↵ ‡ Although our comparison is implied by theory, one can perform the data-mining exercise and compute this same statistic for all four comparisons created by holding out one group, and comparing to the pooled others. When doing so, only the hypothesized comparison is significant (P < 0.05), whereas the others all have P values in excess of 0.15 (all Bonferroni corrected for four comparisons).

↵ § One can posit a testable “difference-in-differences” extension of the three-way interaction hypothesis. In particular, alcohol-intolerant males would be expected to show greater improvement in self-control because of regular exposure to drinking environments than would alcohol-tolerant males. We denote this hypothesis 2a, and find evidence supporting it using a slope test (65, 66) (see SI Appendix, Table S8 and related discussion).

↵ ¶ The model described by column 4 of SI Appendix, Table S4 is supported by the theory as well as a data-based stepwise regression procedure (SI Appendix, Table S5). SI Appendix, Table S5 shows that the two-way interactions can be significant when entered individually. The reason is their high correlation, as high as 0.86, with the three-way interaction. SI Appendix, Table S5 also shows gender and the three-way interaction are chosen for the model first, and conditional on their inclusion no two-way interaction contributes significantly to the model.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1610902114/-/DCSupplemental.