With marijuana now legal in Massachusetts, many people may not think twice about lighting up, but a new study may raise concerns for breast-feeding women.

The study revealed that traces of marijuana can be found in a woman’s breast milk up to six days after use, researchers said.

There isn’t much information on what happens to babies if they ingest marijuana-contaminated breast milk, said Christina Chambers, senior author of the study, which was published this month in the journal Pediatrics.

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But some research has raised concerns that such milk could cause cognitive and behavioral deficits in babies, said Chambers, a pediatrics professor at the University of California, San Diego.

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Researchers at the university examined samples of breast milk from 50 women who used marijuana either daily, weekly, or sporadically. Inhalation was the most common method of intake.

The women donated their milk to Mommy’s Milk — a research repository at the university. They also filled out questionnaires on their exposure to the drug in the 14 days before their milk donation.

The psychoactive part of marijuana, THC, was found in 34 of the samples. The women who gave those samples reported using marijuana up to six days before, researchers said.

Cannabinoids like THC bind to fat molecules. Human milk is composed of 3 to 5 percent fat, researchers said.

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The number of times a woman uses marijuana a day is a positive predictor of THC concentrations in her milk, researchers said. THC can build up in the body fat of a small child.

“If a child is exposed to low levels of THC in milk daily, there is a concern for accumulation of the various cannabinoids in the nursing infant because of slow elimination from body fat stores and continuous daily exposure,” according to the study.

So exactly what would the effect be on those babies?

“We don’t know, and that’s the missing piece,” Chambers said in a telephone interview Tuesday.

“We found that the amount of THC that the infant could potentially ingest from breast milk was relatively low,” she said in a statement, “but we still don’t know enough about the drug to say whether or not there is a concern for the infant at any dose.”

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Chambers emphasized that pediatricians are concerned as findings like hers emerge that some women might stop breast-feeding so they can continue to smoke marijuana.

“We run the risk of them deciding to stop breast-feeding, something we know is hugely beneficial for both mom and baby,” she said.

A new American Academy of Pediatrics report recommends breast-feeding even if mothers are using marijuana. But the report encourages mothers “to cut down and quit,’’ Dr. Seth Ammerman, a report coauthor and Stanford University pediatrics professor, told The Associated Press.

‘‘In counseling patients about this, it’s important to be nonjudgmental but to educate patients about the potential risks and benefits,’’ Ammerman said.

As more states legalize marijuana, its use is increasing along with the ‘‘false impression’’ that it is safe, the academy’s report says. Ammerman said caution makes sense, given the uncertainties.

Chambers said her study should be a stepping stone for future research.

“Are there any differences in effects of marijuana in breast milk for a 2-month-old versus a 12-month-old, and is it different if the mother smokes versus eats the cannabis?” Chambers said.

Those questions and others need answers, she said, especially since the World Health Organization recommends breast-feeding for up to six months.

Research has shown that breast-fed infants can benefit from a reduced risk of obesity, asthma, and sudden infant death syndrome, as well as improved immune health and performance on intelligence tests, Chambers’s study said.

Material from Globe wire services was used in this report. Katie Camero can be reached at katie.camero@globe.com. Follow her on Twitter @camerokt_.

Original Article at https://www.bostonglobe.com/news/science/2018/08/30/traces-marijuana-found-breast-milk-raising-concerns-for-new-mothers/MMQaKG7T9hBGR5ht4caoYK/story.html