A 92-year-old woman found dead in the Avon Gorge last week had been "exhausted" by requests for money from different charities, a friend has said.
Poppy seller Olive Cooke was found two days before the 70th anniversary of VE Day.
Her friend Michael Earley said she had been "under pressure" from requests, but she had also suffered ill health.
The PM called her an "incredible woman" and urged fundraising regulators to look at how they could have helped her.
David Cameron, who presented Mrs Cooke with a Points of Light award last year for being the UK's longest-serving poppy seller, also said she had "worked tirelessly for the charities she supported".
He said: "I know there is a code that is meant to protect people from feeling pressured by charities and I hope the Fundraising Standards Board will look at whether any more could have been done to prevent this."
Responding to the tragedy, fundraising organisations said they would see what lessons could be learned.
Police confirmed a body was found in Avon Gorge on 6 May and had been referred to the Avon coroner as a "sudden death".
An inquest will be opened at a later date.
Last year, Mrs Cooke told the Bristol Post she spent much of her pension on charity donations but was receiving an "overwhelming" number of letters and phone calls asking for more.
She believed charities were passing on her details to others.
Mr Earley said Mrs Cooke was being sent 180 letters a month and was plagued by phone calls.
He told BBC Radio Bristol that while he would not blame her death entirely on charities "pestering" her - she had been "under pressure".
"It was a combination of things, she also had ill health," he said.
Mr Earley said he had thrown out two bags of letters asking for money and Mrs Cooke's phone would constantly call with requests for donations. At one stage, she had 27 direct debits going to different charities, he said.
"In the end, she wouldn't answer the phone. That's what caused a little bit of anxiety. Of course, the next thing we knew, Olive passed away.
"She was exhausted by this situation."
It has also been reported that Mrs Cooke was hit hard by the loss of £250 she had sent a relative, which had apparently gone missing in the post.
'Incredibly sad story'
BBC Radio Bristol's Nigel Dando spoke to Mrs Cooke's granddaughter Louise, who said while she believed the charity letters were probably a factor, Mrs Cooke had also been in ill health.
Mrs Cooke, who lived in Fishponds, lost her first husband in World War Two.
She sold poppies for the Royal British Legion (RBL) charity appeal for 76 years and had been presented with the Lord Mayor's Medal for her work.
Olive Cooke's war memories
"I met my future husband, Leslie Hussey-Yeo, in October 1939. He only had a year left in the Navy when the war started, but he had to stay on. So we married a year later - I was 18-and-a-half. He had 10 brothers and sisters. He and two brothers went to Greenwich Naval school. The eldest brother was killed on the Royal Oak.
"We just had two-and-a-half years together when he was killed on the HMS Thunderbolt. It was lost in the Sicily invasion, March 1943, by depth charge."
Read more about Mrs Cooke's wartime experiences on WW2 People's War.
Roger Duddridge, RBL county chairman in Somerset, told the BBC Mrs Cooke was "a beautiful person" whose death had "shaken us all".
"She was such a giver of life, anyone that was in distress or that needed help, she would give money to," he said.
Politicians have expressed concerns about the case. Conservative MP for Filton and Bradley Stoke Jack Lopresti, who presented Mrs Cooke with an award last year, said he was troubled by the level of calls and letters she had received. The Army veteran said he would write to the police and crime commissioner about the case.
And Kerry McCarthy, Labour MP for Bristol East, said she would be contacting the Charities Commission.
"I will certainly do all I can to follow up on reports that Olive felt besieged by begging letters and calls from charities, to which she had been so generous in the past," she wrote on Facebook.
"I will speak to the Charities Commission about this. I will also be contacting the lord mayor and others about what we can do to commemorate Olive's lifelong work."
Fundraising Standards Board chief executive Alistair Mclean told the BBC that people who did not wish to be contacted by charities could sign up for the Telephone Preference Service and the Mail Preference Service - or get their families to do so on their behalf. He said while charities had to raise funds, "no-one should ever feel under pressure to give".
"This is an incredibly sad story and our hearts go out to the family concerned," he said.
The Institute of Fundraising (IoF) Standards Committee later said it would bring together representatives from across the charity sector to review the case.
Peter Lewis, chief executive of the IoF, said: "Fundraisers know that it is absolutely critical to maintain public trust and confidence in charities.
"An important part of this is to fundraise in the right way and to the highest standards.
"[We] will review any learning following Mrs Cooke's sad death to make sure that our rules and guidance for fundraisers are as robust as they can be."