A major study looking at the link between anorexia and genetics is underway, and around 400 New Zealanders' are expected to take part.

The research will use test results from 13,000 people across the world, to try and establish which genes are connected with the illness.

It's estimated around 21,000 New Zealanders suffer from anorexia, which is characterised by an obsessive desire to lose weight.

Visiting professor doctor Cynthia Bulik said people often think it's a mental condition but that's not true.

“People would never choose to have this illness – it’s deadly,” she said.

“Our job is to get out there and clarify to people that this is a biologically based illness.”

Ms Bulik said medication targeting the genes which contribute to anorexia could soon be developed. She estimates there's around 100 genes or more that could be accountable.

“Hopefully once we identify those pathways we’ll be able to develop medications which target the core biology of the illness.”