Milk contributes to iron deficiency in New Zealand newborns

Pregnant women who drink three or more servings of milk per day might put their babies at risk of being iron deficient during an important phase of their development, according to new research from Growing Up in New Zealand

Iron is essential for healthy brain development, and a lack of the nutrient in babies and toddlers, when the brain is developing rapidly, is associated with subsequent small but important differences in brain function and in child behaviour and learning.

The paper published today in the New Zealand Medical Journal (NZMJ) found that 7% of New Zealand newborns are iron deficient, and established that iron stores are lower in babies whose mothers consumed higher quantities of milk during their pregnancy.

“While milk is an important source of calcium it is a poor source of iron.  Milk is also quite filling and so can reduce the appetite for others foods that are better sources of iron,”  explains Associate Professor Cameron Grant, a paediatrician at Starship Children's Hospital and the senior author of the paper. “Pregnant women with iron deficiency are more likely to go into premature labour or deliver a baby with low birth weight.  They are also more likely to be iron deficient while they are breastfeeding.”

Using cord blood samples from 131 children from the Growing Up in New Zealand birth cohort, Dr Grant and his team determined the iron status of each newborn. The results were compared to information collected in face-to-face interviews with the mothers to establish whether maternal and infant demographics, pregnancy health and history, and dietary factors were associated with iron status at birth.

“Although the sample of children we tested was quite small, they are broadly generalisable to all children born in New Zealand today, and the results give us a good indication of iron deficiency as an issue,” says Dr Grant.

Iron deficiency is the most common micronutrient deficiency worldwide, with pregnant women and children under five most at risk. The condition is twice as common in young New Zealand children (6 months to 2 years old) than it is in children of the same age living in Australia, Europe or the United States.

Although there is currently no data available for mothers-to-be in New Zealand, the frequency of iron deficiency among women at childbearing age (over 15 years) has increased from 3% in 1997 to 7% in the most recent survey, conducted in 2008/09.

To prevent negative effects on their child’s early development, Dr Grant recommends that pregnant women who drink large amounts of milk each day take iron supplements. “An alternative would be to increase the nutrient content of milk consumed by mothers-to-be to keep both the mother and child healthy.”

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Other scientific papers on nutrition in pregnancy from Growing Up in New Zealand

  • Morton SMB, Grant CC, Wall C R, Atatoa Carr PE, Bandara D K, Schmidt JM,  Ivory V, Inskip HM, Camargo Jr CA. (2014). Adherence to nutritional guidelines in pregnancy: Evidence from the Growing Up in New Zealand birth cohort study. Public Health Nutrition, FirstView Article, 1-11. doi:10.1017/S1368980014000482
  • Morton SMB, Grant CC, Atatoa Carr PE. (2013). Too many left at risk by current folic acid supplementation use: evidence from Growing Up in New Zealand. Aust N Z J Public Health37(2), 190-191. doi:10.1111/1753-6405.12042

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