Limiting milk intake -- or avoiding it altogether -- during pregnancy may restrict essential nutrients and negatively affect fetal development, say the authors of a new study.

They found that the newborn babies of women who drank more milk were heavier than those who drank less.

The report, whose authors included Dr. Kristine Koski, director at the School of Dietetics and Human Nutrition at McGill University in Canada, said, "Our study showed that restricting milk or vitamin D intake during pregnancy lowered infant birth weight in otherwise healthy, nonsmoking, well-educated mothers."

'This is an important finding, because increasing numbers of women are restricting milk consumption during pregnancy believing that it will lower fat intake, minimize weight gain, treat self-diagnosed lactose intolerance or prevent their children from developing allergies. Mothers and health professionals need to understand that this dietary practice may restrict essential nutrients and negatively affect fetal development," the study advised.

Produces Strong Bones

The study involved about 300 women aged 19 to 45 who attended prenatal classes in Calgary, Canada, between May 1997 and June 1999.

The women were asked whether they restricted dairy products for any reason and, to try to eliminate other factors from the study, those chosen were all healthy, well-educated women who smoked little or not at all and who weighed about the same.

Of the 300 women, 72 said they had been drinking less than a cup of milk a day during their pregnancy.

A cup of milk was chosen as the benchmark because there are about 2.5 micrograms of vitamin D in a cup of milk, which is significantly below the daily intake of 5 micrograms recommended by the Canada Food Guide for Healthy Eating.

Vitamin D is considered important in skeletal growth and in producing strong bones.

Exposure to Sunlight

The study found that each daily cup of milk added, on average, 41 grams (about 1.4 ounces) to the weight of the baby when it was born.

"Although most nutrients in milk may be replaced from other foods or with supplements, vitamin D is found in few commonly consumed foods except for milk," it said.

It acknowledged that exposure to sunlight can be a source of vitamin D -- sunlight can generate vitamin D in the skin -- but added this was a "seasonally unreliable source, particularly when the exposure of skin to sunlight is limited."

It concluded, "Medical practitioners should query pregnant women about their consumption of milk and multivitamins, specifically those containing vitamin D, to avoid the risk of lowered birth weight as a result of insufficient intake, particularly when and where sun exposure is limited."