A study has found that one in five New Zealand babies are at risk of rickets due to low vitamin D levels.
The study, written by University of Auckland associate professor Cameron Grant has been published in the American journal Pediatrics.
Mr Grant says New Zealand has a higher rate of vitamin D deficiency than other countries because food is not fortified with the vitamin, and it is not routinely recommended.
The study reports breast-fed babies in Maori and Pasifika communities are more at risk because these children could be covered up or veiled when outside.
Most vitamin D comes from exposure to sunlight.
It says a mother's vitamin D level during pregnancy determines the vitamin D status of her newborn.
Dr Grant says to achieve normal levels, supplements should be given to both mothers and their babies.