Gut Check is a periodic look at health claims made by studies, newsmakers, or conventional wisdom. We ask: Should you believe this?

The claim

Children of women who ate little or no meat while pregnant are more likely to abuse alcohol, tobacco, and marijuana at age 15 than are children of mothers who did eat meat.

Tell me more

Researchers analyzed data from 5,109 women and their children in a long-running study in England called ALSPAC (the Avon Longitudinal Study of Parents and Children), which has gathered years of data on what women did while pregnant and their children’s health. The less meat the women ate while pregnant, the more their children’s risk of drinking, smoking, or using marijuana as 15-year olds, Dr. Joseph Hibbeln of the National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health and his colleagues reported on Wednesday in Alcoholism: Clinical and Experimental Research. (They were funded by the U.S. and U.K. governments and a charity, not meat producers.)

Roughly 10 percent of the 15-year-olds smoked at least weekly, drank enough to have behavioral problems, or used marijuana “moderately.” But teens of meatless moms were 75 percent more likely to have alcohol-related problems, 85 percent more likely to smoke, and 2.7 times as likely to use marijuana compared to teens of mothers who’d eaten meat while pregnant.

advertisement

The researchers suspected that any adverse effect of mom’s forgoing meat while pregnant involves vitamin B12, which is abundant in meat but not plants. They therefore dug deeper into their data, comparing two groups of women: those with a high-functioning form of the gene that brings B12 into both their cells and their fetus’s, and those without the high-functioning gene. In the latter, B12 doesn’t reach their cells or their fetus’s very well regardless of what they eat, so it shouldn’t matter if they got lots of B12 (in meat) or not.

Here’s what the researchers found: Among moms without high-functioning B12 genes, there was no difference in their teens’ risk of substance abuse whether they’d eaten meat while pregnant or not. The vegetarian mom/substance-abusing teen association held only among women with high-functioning B12 genes, in whom eating meat or not would affect how much B12 their cells and their fetus’s got. That seemed to strengthen the case for an association between a meatless, low-B12 pregnancy and children’s later substance abuse.

advertisement

Really?

Of course, what mom eats while pregnant can affect the child’s health. B12 helps insulate neurons, including in the developing brain, which may be why too little seems to leave kids with impaired cognitive and social development. That might leave children with poorer impulse control and other deficits that can make them abuse drugs and alcohol. “I’m not surprised by the results,” said University of Oxford physiologist John Stein, who was not involved in the new study.

Other experts raised questions. While mostly well-regarded, ALSPAC has also produced head-scratching and possibly wrong findings, such as linking pregnant women’s acetaminophen use to their child’s behavior problems or moms’ eating fish and children being obese. With as much data as ALSPAC generates, statisticians worry that mining it all can produce spurious correlations, things that are linked only coincidentally and not in a meaningful way.

Another issue is that ALSPAC had pregnant women fill out questionnaires about their diet. It didn’t verify their reports or measure their B12 levels. That raises the possibility that women misremember what they ate while pregnant. “Self-reporting dietary intake and substance use/abuse can have errors,” said nutritionist Susan Levin of the Physicians Committee for Responsible Medicine, a nonprofit that advocates vegan diets. As a result, many nutrition studies based on self-report reach erroneous conclusions.

Because this is an observational study, the researchers can’t rule out the possibility that “women who choose to be vegetarian are different from those who do not,” Oxford’s Stein said. What kind of home a family lived in (publicly subsidized or owned), maternal education, and parents’ social class (white collar or manual laborer) was associated with at least as great an elevated risk of a child’s substance abuse as mom’s meatless pregnancy.

“No one would disagree that B12 is critical in the health of the fetus and beyond,” Levin said. “While B12 may well play a role [in teens’ substance abuse], many other factors could contribute to the findings, such as religion and personality traits of the parents and children, which were not measured or accounted for.” Hibbeln said he and his colleagues “are very sensitive to issues associated with confounding,” and is confident that a meatless pregnancy affects risk of substance abuse independently of other factors.

Is the parenting style of vegetarian moms different from that of meat-eating moms in a way that would affect kids’ likelihood of drinking or smoking? In fact, the researchers found that moms who avoided meat were (contrary, perhaps, to stereotype) not more permissive but more protective, keeping an eagle eye on their kids. That should decrease the kids’ risk of substance abuse, yet these were the mothers whose teens were more likely to smoke and drink.

“Many, many factors contribute to children’s substance use,” said Maureen Black of the University of Maryland School of Medicine, an expert on B12 and brain development. It’s a “long stretch to link it to maternal meat consumption during pregnancy.”

The verdict

The link between mom avoiding meat during pregnancy and her child’s later risk of substance abuse is an intriguing but unproved idea, and in any case the study authors say pregnant women don’t have to be carnivores to modify any such risk from going meatless, since B12 is also found in supplements.