The Duke of Cambridge has labelled the level of suicide among men under 40 an "appalling stain on our society" as he continued his campaign to raise awareness about mental health.
Addressing the Guild of Health Writers conference, William told the journalists that if the deaths were the result of cancer or road accidents there would be a "national outcry".
William, who was joined by Kate at the central London event, said "silence can kill, but talking can lead to help and support", as he backed the royal couple's Heads Together mental health campaign to get the nation opening up about their problems.
The Cambridges and Prince Harry are spearheading the initiative and in recent weeks have stepped up their campaigning, attending numerous events with a mental health theme, from highlighting the support available to military veterans to encouraging primary school children to support their peers.
The Duke told the delegates at the conference, themed The Anxiety Epidemic: "You may be wondering why Catherine, Harry and I got involved in this topic in the first place. Mental health is traditionally not a mainstream subject, after all.
"For me personally, it was a gradual awakening over many years through work I've been privileged to witness with vulnerable young people - the homeless, the unemployed, those who are unable to fulfil their potential.
"But I got interested in mental health for another reason. One that was related to my work as an air ambulance pilot. It was suicide, a subject that is so often hidden.
"The suicide rate among young men in this country is an appalling stain on our society. Suicide is the biggest killer of men under 40 in this country. Not cancer, not knife crime, not road deaths - suicide.
"If one of these other issues took so many young lives, there would be a national outcry."
William told the delegates that when he, his wife and brother started looking at the issue they talked to eight mental health charities to see what they could do to help.
The Duke said: "At the moment, on average it takes a sufferer 10 years to admit to a problem. This means that what often starts as a fairly minor issue becomes something serious and medical after time.
"What these charities told us was that silence can kill, but talking can lead to help and support."
William said that over the next few months they would encourage people from all walks of life to record a video about what it feels to talk - in a bid to encourage others to do the same.
A range of speakers later addressed the delegates, from Jacqui Marson, a chartered counselling psychologist, who talked about the physical effects of anxiety, to Paul Farmer, chief executive of the mental health charity Mind, who highlighted how anxiety affected society.
Before the event William and Kate, who wore an outfit by Oscar de la Renta, chatted to guests.
In a lighter moment, the Duke joked about Sunday's London Marathon, where he, Harry and Kate raced against each other as they supported runners taking part in support of Heads Together.
The Duke said of Harry, who easily won their race: "He hasn't sprinted like that since he was 18."