The vast majority of New Zealanders suffering from coeliac disease don't know they have it

Coeliac New Zealand, says four out of five coeliacs are undiagnosed.

The condition means gluten causes the immune system to attack cells in the small bowel.

Impacts include constant nausea or fatigue, and infertility.

Paediatric gastroenterologist Andrew Day, says many are undiagnosed because they don't have symptoms, or downplay them.

He says it's like a ticking time bomb in the background.

He's spoken to many adults diagnosed in later life after ignoring symptoms for years.