Two Dunedin parents who are fighting for the custody of their daughter say vitamin D deficiency caused her multiple broken bones, not child abuse.

Their case has highlighted a growing problem of children being born with brittle bones because of vitamin D deficiency, and the risks of parents being labelled child abusers as doctors try to understand what caused broken bones.

Child, Youth and Family (CYF) removed the couple's 14-week-old daughter from them after doctors raised alarm bells over the girl's fractured skull, limbs and six broken ribs.

When the case went to the Family Court, doctors were at odds over whether the infant's injuries were caused by trauma or a rare case of a baby so lacking in vitamin D in the womb that it was born with the Victorian era disease of rickets.

Vitamin D helps calcium to be absorbed, making bones stronger.

The Family Court ruled in favour of the CYF decision to place the girl in the care of an aunt for her protection.

Judge John Coyle said there was no evidence the "doting parents" were mistreating their daughter, but rejected rickets as a cause and said he could only conclude one of the parents caused her broken bones.

The debate is now likely to play out at an appeal hearing at Dunedin High Court later this year.

In a High Court decision released last month, Justice Graham Panckhurst granted the Dunedin parents permission to use evidence from a medical expert who testified in a landmark British case.

Justice Panckhurst said there were "striking similarities" between the cases, including the children's ages and type of fractures. No court date has been set.

In April 2012, two British parents were cleared of killing their 4-month-old son, Jayden Wray, who inherited rickets from an undiagnosed vitamin D deficiency in his mother and died from a head injury in July 2009.

A London Court ruled the boy's injuries were caused by rickets and granted the parents custody of their daughter, who had been in care since birth.

The British case put the spotlight on vitamin D deficiency and raised concerns that hospital specialists were missing potentially deadly cases of the diseases.

Dunedin paediatrician Dr Benjamin Wheeler, who testified at the Family Court hearing, still insists the New Zealand girl's injuries could not be explained by vitamin D deficiency though he admitted the girl had a mild to moderate case of rickets, proven by radiology images of her bones. Eight doctors who gave evidence at the Family Court debated whether the girl's injuries were caused by abuse or vitamin D deficiency.

Judge Coyle said it was a complex case and "incredibly difficult". The parents were caring, responsible and intelligent people and there was no evidence of mistreatment but "despite the counter-intuitive factors that I have referred to, the inescapable conclusion is that [the child's] non-accidental injuries were caused by one of her parents".

WHAT IS VITAMIN D DEFICIENCY?

The main source of vitamin D is synthesis of cholesterol triggered by the sun.

There are growing concerns the sun-safety and indoor working life are leading to an increasing number of people developing vitamin D deficiencies.

People who don't get enough vitamin D can develop rickets, which causes bowed legs, knock knees and bone weakness.

If a mother is deficient of vitamin D, her child may also lack the essential vitamin.

You can top-up vitamin D through sensible sun exposure and eating foods high in the vitamin D.

Having darker skin, living in the lower South Island and wearing clothing that covers most of your body increases the risks of developing a deficiency.

ALARMING GROWTH IN BRITTLE BONES

New Zealand experts are alarmed by an increase in vitamin D deficiency in New Zealand.

Starship Children's Hospital paediatrician Dr Cameron Grant said one in five newborns was at risk of rickets due to low levels of vitamin D, adding that the condition was not always obvious.

He said it could be difficult to determine between fractures caused by rickets and those caused by child abuse.

"You would look to see how severe the vitamin D deficiency was and evidence of it affecting the bones. The bones would look thinner and paler because there's less calcium in them."

Massey University nutrition lecturer Dr Pamela Von Hurst said vitamin D deficiency was an increasing problem for the country.

"What we have essentially right now is a borderline vitamin D deficient population," she said.

"Vitamin D is absolutely essential for calcium to be absorbed into the body and laid down in the bones.

"Without it, the bones stay very soft."

The Ministry of Social Development, which oversees CYF, refused to comment on the case while it was still before the High Court, nor would they say whether the child was still in the care of her aunt.

- © Fairfax NZ News