Newswise — Individual genetic make-up, roommates’ drinking behavior, and how much individuals thinktheir friends are drinking all influence students’ own alcohol use, according to new findings from the ‘Spit for Science’ project at an urban campus university.

Excessive drinking, considered a rite of passage by many campus students, risks many consequences including memory blackouts, injury, academic problems, and long-term health issues. Several factors influence students’ alcohol use, including having peers who drink heavily ─but as heavy drinkers tend to choose to associate with like-minded others, this may be a correlative association, rather than a causal effect of time spent with heavy-drinking peers. Genes are also known to play a role, with alcohol-use behaviors influenced by numerous genetic variants that individually have small effects.

The new analysis explored the effect of multiple aspects of peer drinking, as well as genetic predisposition, on alcohol use by individual students. To help disentangle cause from correlation, freshmen roommates who had been randomly paired by college housing services, rather than those who self-selected roommates, were studied. Students answered questions on their alcohol use at the start of the fall semester, provided saliva for DNA analysis, and completed a follow-up survey in the spring semester. Peer drinking was assessed by asking students for their perceptions of friends’ drinking behavior, and from the actual level of drinking reported by their roommates in the fall. The average alcohol intake in the students’ halls of residence also was determined, as a measure of the wider drinking culture.

Among the 755 participating students – 367 roommate pairs and seven triples – average alcohol use increased significantly between the fall and spring semester of the freshman year. Researchers identified three factors associated with heavier spring semester drinking among individual students: greater genetic predisposition*, perceiving higher levels of drinking among peers, and living with roommates who reported high levels of drinking in the fall. Average alcohol use across the residence hall in the fall semester, however, was not associated with individuals’ drinking in the spring, perhaps because students have only limited interaction with many of the individuals living in their residence halls, which at this urban university, were high rises.

These findings underscore the importance of genetic predisposition on individual alcohol use and the potentially causal influence of peer drinking – especially how much students think others are drinking, evenmoreso than how much their roommates really are drinking! They may also inform and guide campus prevention and intervention programs aimed at reducing harmful drinking among students.

*Genetic predisposition was calculated as a ‘polygenic score’, after analyzing the students’ DNA for thousands of genetic variants that have each been previously associated with greater alcohol use.