Could Your Birthday Make You Prone to Substance Abuse?

From the WebMD Archives

July 24, 2000 -- If you were born in October, do you have more of a chance of being dependent on alcohol or drugs than your friend who was born in February? Could the phrase "What's your sign?" be replaced by "What's your birth month?" Perhaps, says a new study from the National Institute on Drug Abuse.

Researchers from the National Institute on Drug Abuse and the University of Massachusetts at Amherst looked at a database of more than 40,000 people to assess drinking and drug-related beliefs, attitudes, practices, and behaviors. The researchers wanted to find out whether the likelihood of someone being dependent on alcohol, or of abusing alcohol or illicit drugs, correlated to the season in which they were born.

Though the findings are still speculative, "basically, what we found was that the [men] with a history of alcohol dependence -- [and] it did not have to be current, by the way -- were about 10% more likely to be born in the final quarter of the year," David Newlin, PhD tells WebMD. Newlin is a research psychologist in the intramural research program at the National Institute on Drug Abuse in Baltimore.

This finding did not hold true for alcohol-dependent women. But when the researchers looked at the data for illicit drug users, both men and women were 10% more likely to be born in the final quarter of the year, from October to December.

The theory behind this, Newlin says, is that "anything seasonally related during [the mother's pregnancy] or [the child's] early infancy that would produce an insult, probably to the brain, but also to the liver and other organ, might increase the risk for alcohol dependence and illicit drug use." These "insults" could be any number of things that might occur during pregnancy or early infancy: hormonal fluctuations, extremes of temperature, or viral infections.

Newlin cautions that this seasonal effect appears to be small, and that heredity is a major factor in these conditions, especially alcohol dependence. In fact, someone with a family history of alcoholism has a three to five times greater chance of becoming an alcoholic than someone with no such history. But environment is also known to play a big role, and the seasonal effect seen by the researchers is definitely environmental, Newlin tells WebMD. So further study is needed into how birth season and other environmental factors, as well as heredity, come into play.


Still, is this enough to say that parents should plan the season of their baby's birth to ward off potential alcoholism or drug dependence?

Newlin says this idea is not warranted by the current study's findings. He and his colleagues are looking to repeat these findings in other study groups from the U.S., as well as in an Australian group -- in which the seasonal effect should come up exactly the opposite from this study, as seasons there are the reverse of those in the U.S.

The effect of birth season has also been studied in schizophrenia, as well as in other psychiatric disorders.

"An excess of late winter and early spring births has been demonstrated repeatedly for schizophrenia," Newlin and his co-author, Abbie E. Goldberg, note in their study. Other studies have shown that schizophrenics were more likely to be born in winter months following outbreaks of viral infections. But it's still unclear what these observations might mean for diagnosing or preventing these disorders.