The former That's Life host said The Silver Line helpline - set up as a "ChildLine" for older people - was already having a "transformational" effect on the lives of thousands of the elderly -and had revealed a "huge and unmet need".
Most callers lived alone and more than a half, 53%, said they had no-one else to speak to other than the helpline.
Research into 100 callers showed nearly half, or 48%, often spend more than a day without talking to anyone and 11%, or a little over one in 10, often spend more than a week without having a conversation.
One in five, or 20%, said they were not in touch with their family or had no family. More than two thirds, or 68%, said they were reluctant to ask their own families for help because they did not want to be a "burden."
Ms Rantzen said:"The shocking fact is that Britain has become too busy to find time for our older people.
"Older people need time to talk, time to listen, time to value them.
"Silver Line callers say that being encouraged to ring The Silver Line made all the difference."