Many pregnant women in New Zealand should be taking vitamin D supplements to ensure their babies are not at risk of rickets.
Young breastfed infants of Maori or Pacific Island women, or infants of women with dark skin or who are often covered or veiled when outdoors, are at the greatest risk of having low vitamin D levels.
The mother’s vitamin D level during pregnancy determines the vitamin D status of her newborn baby and remains an important determinant of vitamin D status while the infant remains exclusively breastfed.
A study to determine the optimum vitamin D dose for pregnant women and infants has recently been completed in Auckland and was published this month in the American Academy of Pediatrics journal ‘Pediatrics’.
The study showed that recommendations for vitamin D supplements during pregnancy and infancy may be insufficient to achieve optimal vitamin D status in New Zealand infants.
As one in five New Zealand infants has a vitamin D level at birth that is low enough (< 25 nmol/L) to put them at risk of rickets, these study findings are particularly relevant to this generation of New Zealand newborns.
Study author, Starship Paediatrician Dr Cameron Grant, an Associate Professor from the University of Auckland, says that vitamin D deficiency has re-emerged in recent years as a public health problem around the world.
"New Zealand is a country that neither fortifies its food with vitamin D nor recommends vitamin D supplements be taken routinely, and so we have a higher rate of vitamin D deficiency than many other countries," he says. "We also have not had good data on which to base recommendations for vitamin D supplement use by pregnant women and young infants."
"We have shown in this study that if we want to achieve normal vitamin D status in babies in New Zealand we should be giving vitamin D supplements." In New Zealand more than 90 per cent of our vitamin D is obtained from sunlight, but, it is impossible to use sunlight as a safe and reliable source of vitamin D throughout the year, says Dr Grant.
In recently published research on pneumonia in Auckland, Dr Grant has shown that children who spend less time outdoors are at increased risk of pneumonia. Thus low vitamin D level could be one of the reasons for the higher rates of pneumonia seen in Pacific and Maori children.
The study in ‘Pediatrics’ reported on the findings from a randomised double blind placebo controlled trial which determined what dose of vitamin D was necessary during pregnancy and early infancy to achieve normal vitamin D levels in infants. A vitamin D level of at least 50 nmol/l is considered to be normal.
"The recommended daily amount of vitamin D for infants is based on the amount of vitamin D in a teaspoon of cod liver oil," says Dr Grant. "Cod liver oil was introduced in the 1930s when it identified that there was something in it that could prevent rickets."
"A teaspoon of cod liver oil per day prevented rickets. One teaspoon of vitamin D contains 400 international units of vitamin D. This is the amount considered adequate for infants in Europe and North America," he says.
This study, done in collaboration with Harvard University, the University of Otago, Kidz First Children’s Hospital and Lead Maternity Carers Limited was carried out in New Zealand because we do not fortify our food with vitamin D or routinely take vitamin D supplements.
Participants were randomly assigned to three groups - higher dose vitamin D, lower dose vitamin D or placebo. Mothers were enrolled at 27 weeks pregnant and took the study medicine until their infant was born. Their infant then took the study medicine until age 6 months.
"We started during pregnancy because you need to take vitamin D for several weeks before vitamin D reaches a steady level in your body and we wanted to ensure that this steady state was present at birth. If we had waited until the baby was born to start vitamin D we know that some of them would already be vitamin D deficient," says Dr Grant.
In the lower dose group each mother was given 1000 international units of vitamin D per day and her baby was given 400 international units per day from birth to age 6 months. In the higher dose group each mother was given 2000 international units of vitamin D per day and her baby was given 800 international units per day from birth to age 6 months.
Recommended daily vitamin D doses vary internationally for pregnant women from 200 to 800 international units and for infants from 200 to 400 international units. In New Zealand the recommendations are for 200 international units of vitamin D per day during pregnancy and infancy.
The results of the trial showed that both the higher and lower vitamin D dosing regimens increased the proportion of infants with vitamin D concentrations of 50 nmol/l or greater. The higher dose of vitamin D maintained normal vitamin D levels for longer - up to six months, whereas the beneficial effect of the lower dose of vitamin D was only seen to age 4 months.
Now that this study has determined the vitamin D dose necessary to achieve normal vitamin D status the health effects of vitamin D supplementation can now be determined, says Dr Grant.
The effect of vitamin D status at birth on health during early childhood is being determined within New Zealand’s new birth cohort study ‘Growing Up in New Zealand’ (www.growingup.co.nz).
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