Churchgoers have been found to have lower rates of drinking and smoking than those who spend their Sundays elsewhere. Now a new study suggests that for adults, it may not be church attendance itself that explains much of the phenomenon. It might be genes.

The study, which included nearly 1,800 adult male twins, found that in adolescence, the relationship between church attendance and lower rates of drinking and smoking appeared largely a matter of “shared” environment - those factors influencing both members of a twin pair.

That is, teenagers who attended church regularly were more likely to want to follow their parents’ wishes and conform to community expectations.

By adulthood, however, those environmental influences had faded, the researchers found. Instead, genes seemed to account for the relationship between church-going and lesser alcohol and nicotine use.

In this case, genes may enter the picture via their influence over a person’s natural temperament, the researchers write in the American Journal of Psychiatry. Many adults who continue to regularly go to church, they speculate, may also be the sorts who would limit their drinking and avoid smoking.

“Church attendance is one of the strongest correlates of substance abuse,” lead researcher Dr. Kenneth S. Kendler, of the Virginia Commonwealth University School of Medicine in Richmond, told Reuters Health.

“Understanding the underlying nature of this association is important because of what it tells us about the causes of substance use,” he said.

The study included 469 identical twin pairs and 287 pairs of fraternal twins, all of whom were interviewed twice over six years. The men were asked about their current church attendance and smoking and drinking habits, as well as their habits during adolescence.

Twin studies like these allow researchers to disentangle the effects of genes, shared environment (like home life and parenting practices) and non-shared environment (such as friendships and other factors unique to an individual) on a given behavior or disease risk.

Identical twins share all of their genes, while fraternal twins share about half of their genes, on average. So if genes, for example, hold a stronger influence over a particular behavior than shared environment does, identical twins would be more similar in that behavior than fraternal twins would be.

Kendler’s team found that when it came to the link between church- going and substance use, the roles of environment changed over time.

By adulthood, shared environment seemed to have almost no role.

Instead, genes largely explained the relationship, with some role of non-shared environmental factors also being apparent. As adults, the researchers point out, twins’ personal relationships, with friends and partners, likely take on more importance than the shared family influences that were key in the teen years.

It’s not clear how broadly applicable these findings might be, the researchers note. All of the study participants were white men, and most were Protestant, 60 percent of whom were Baptist or fundamentalist.

“Our results,” the researchers write, “may not extrapolate to other populations with different patterns of religious affiliations.”

SOURCE: American Journal of Psychiatry, October 2009.