Milk intake in pregnancy

[The authors respond:]

We appreciate Tushar Mehta's concerns. Our study1 was designed as a diet study and therefore we measured both supplement and food intakes of many nutrients, using the dietary reference intakes recently developed by Canadian and US experts.2 The media's “milk slant” on the article drew in readers and listeners, but this was a study about a dietary requirement for vitamin D.

Initially we examined the quality of the diets of pregnant women who were in increasing numbers restricting their intake of fortified milk, which was one of the few good sources of vitamin D in the Canadian diet in 1998. With the growing recognition that vitamin D deficiency is widespread in North America3^,4 and that a dietary source of this vitamin is required in the winter months, more foods are now fortified with vitamin D, including yogurt, rice and soy beverages, margarine, some infant formulas, meal replacements and ready-to-eat cereals. Use of vitamin supplements is still encouraged, but the pregnant women in our study who needed supplements the most were not consuming them.

Mehta wonders whether the 120-g difference in birth weight that we observed is clinically relevant. At the recent Milk, Hormones, and Human Health Conference sponsored by Harvard University (www.milksymposium.org), preliminary data were presented from the Danish Birth Cohort Study (with 101 042 recruits) showing a higher incidence of both small-for-gestational-age and large-for-gestational-age births with low and high milk intakes, respectively.

Milk is a complex biological fluid requiring further investigation, as more than 1 component could be responsible for its biological effects. In Canada, where pregnant women live at northern latitudes with limited sunlight exposure, vitamin D is one of these important nutrients. One of the consequences of inadequate vitamin D consumption during pregnancy now appears to be reduced bone mineralization in childhood.5 Our study's conclusion that daily intake of vitamin D is required during pregnancy is an important public health message for Canadians.