Japanese medical researchers scanned the brains of 50 young adults and asked them to fill out a detailed survey about their relationship with their parents until the age of 16.

The study, reported in this week's New Scientist magazine, found those with over-protective parents had less grey matter in the prefrontal cortex than those with a more normal parental relationship. Neglect or lack of parental care by fathers - but not mothers - also correlated with less grey matter.

Scientists at Gunma University in Japan said studies of parental bonding suggested high levels of over-protectiveness increased the risk of ''several psychiatric disorders, including schizophrenia and mood disorder''.

They measured the volume of grey matter in the brain's prefrontal cortex against a ''parental bonding index'', calculated from the surveys submitted by young adult participants.

A recent study by Monash University also linked ''over-protective but low-nurturing parents'' to a higher risk of teenage depression. High levels of over-protectiveness appeared to be linked to low levels of self-esteem and anxiety.

The study, published in the British Journal of Developmental Psychology, found teenagers with no depressive symptoms also had high levels of ''cognitive reappraisal''. They were able to think about potentially negative events and reframe them in a more positive way.

The findings of both studies appear to support the arguments advanced by author and Psychology Today editor Hara Estroff Marano in her book A Nation of Wimps: The High Cost of Invasive Parenting.

Marano argued over-anxious parents were sanitising childhood, ''taking all the discomfort, disappointment and even the play out of development'', and making children fearful of discomfort or failure."

For more on this story, see the print edition of today's Canberra Times.