A disease associated with Victorian times has been found in nearly 60 New Zealand children.
Rickets is caused by a Vitamin D deficiency and is a serious bone-growth disorder that can lead to skeletal deformity and seizures.
An Otago University study over three years identified 58 cases of rickets, a third of them in Auckland and Northland.
The study's co-author, Ben Wheeler, said risk factors for the disorder included being under three, having darker skin pigment, being exclusively breast-fed and living in the far South, Auckland and Northland.
Dr Wheeler told Morning Report the number of cases was likely to be higher.
"I guess working at the coal face as a paediatrician and paediatric endocrinologist I see rickets every year, so we knew that it was occurring.
"And in fact probably, unfortunately, our results are probably an underestimate of the real numbers."
Vitamin D is absorbed from food or produced by the skin when exposed to sunlight.
While breast-milk is the optimum nutrition for infants, it has low levels of naturally occurring Vitamin D, said Dr Wheeler. "So those who are breast fed are at higher risk than those who are formula fed."
There was a "double problem" in New Zealand of too much UV from sunlight, leading to high rates of skin cancer and melanoma, but that many children were getting enough sunlight.
"The main message here is that we do think that the sun is harmful in New Zealand, and particularly for those who are very young, I think supplementation is the way forward for them."
Dr Wheeler said at-risk mothers and children need to be better targeted for Vitamin D supplements.
Researchers in Otago's New Zealand Paediatric Surveillance Unit say the study is the first to give a snapshot of the number of rickets cases occurring in children aged under 15 in this country.
Every month, over the period July 2010 to June 2013 inclusive, the researchers asked some 220 New Zealand paediatricians (92 percent of the current workforce) if they had treated any cases of Vitamin D deficiency rickets in the previous month.
The researchers were notified of 73 cases by 38 paediatricians. Their responses to follow-up questionnaires allowed the team to exclude cases that did not meet its strict clinical definitions, or were duplicates.
The researchers identified 58 children with the disease, and analysed anonymised data relating to these patients.
Their findings are newly published in the Australian and New Zealand Journal of Public Health.
Dr Wheeler said there had been mounting concern worldwide that the number of children suffering from Vitamin D deficiency and Vitamin D deficiency rickets was increasing.
The Government said it would be seeking advice from health professionals about what it needed to do to stop growing cases of rickets in New Zealand.