Dr Cheung looked at 225 coroner's reports on closed cases of suicide of those aged 65 and above, between July 2007 and December 2012.
Mental health issues were "usually not the primary concern" raised by patients in their final GP visit, he said.
"The high rate of presentation to general practitioners can provide an opportunity for suicide prevention by better identifying depression and addressing suicide risk in older people, along with managing their physical problems."
"At least 80 per cent of them did not have a terminal illness," he said.
"We don't have a suicide prevention programme for older people [in New Zealand]," he said.
He would also like to see a screening system, including a short questionnaire for patients, put in place to help better identify depression among older patients during GP visits.
Dr Cheung urged greater awareness of depression and its associated risks, and said both patients and GPs could potentially do more to speak about life challenges linked to "feeling down", given that good treatments for depression were available.
About 200 people are attending the three-day conference, which is being held at the Otago Museum, and ends today.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (4pm to 6pm weekdays)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• The Word
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.