A new study involving an Auckland University researcher calls for a major overhaul of the way depression is diagnosed and treated.

The researchers behind the study say that depression is actually 12 distinct diseases, with different causes leading to vastly different symptoms.

Auckland University PhD candidate Severi Luoto said there are several pathways for short term mood lowering to become chronic depression.

"We are able to look at mechanisms underlining that escalation into chronic depression, which are typically caused by a modern, western lifestyle."

He said it changes the way depression should be diagnosed and treated.

"Different kinds of physiological mechanism might underpin different individuals susceptibility to depression."

Luoto said the mechanisms include loneliness, long-term stress, and drugs.