Researchers are calling for full government funding of vitamin D supplements following a study showing southern New Zealand women and their babies are at high risk of vitamin D deficiency.
The study from University of Otago is the first of its kind in the Southern Hemisphere. It recruited 126 women through Dunedin's Queen Mary Maternity Centre from 2011 to 2013.
The findings, just published in the journal Nutrients, found 65 per cent of mothers and 76 per cent of babies were vitamin D deficient, and three of the babies had evidence of rickets.
Vitamin D is essential for foetal bone health, growth, and dental health. The body produces the vitamin when the skin is exposed to UVB rays from the sun.
But during the autumn and winter months, the sun may not be strong enough to produce vitamin D, especially further south, so your body relies on dietary sources such as eggs, liver, oily fish and some dairy to get enough vitamin D.
A lack of vitamin D is also linked to a higher risk of rickets in childhood. Rickets causes soft bones, increasing the risk of fractures and deformities.
The study raised "significant questions" around public health policies, according to lead author Dr Ben Wheeler, of the Dunedin School of Medicine's Department of Women's and Children's Health.
"This is particularly an issue in New Zealand as living further south potentially decreases one's ability to make vitamin D and the country has negligible vitamin D food fortification."
Vitamin D supplements are only considered for pregnant women and breastfed infants considered "at risk" - such as those with dark skin, people who avoid the sun completely, or infants who are breastfed over winter. Certain medications, liver or kidney disease and having a sibling with rickets are also risk factors.
Most Kiwi women and children don't meet these risk factors, Wheeler said.
"However, our results show that in southern New Zealand, in traditionally low risk women and their infants, rates of deficiency are very high. In addition very severe deficiency in infants was also seen, something not previously seen in other similar international studies.''
New Zealand's guidelines should be stronger, Wheeler said. He called for a fully-funded universal supplement for Kiwi women and their children during pregnancy and lactation, especially in the South Island.
Maternal vitamin D status during pregnancy is influenced by a range of factors, including season, skin colour, supplementation, latitude, and potential pregnancy-specific variations in metabolism.
Supplementation studies during pregnancy demonstrate significantly improved infant status at birth and beyond, according to the researchers.
According to the Ministry of Health, around 5 per cent of Kiwi adults are vitamin D deficient and another 27 per cent are below recommended blood levels.
Living in the South Island, particularly south of Nelson-Marlborough, is a risk factor for deficiency, as is having darker skin, covering up or not going outside often.