South Wootton builder Stewart Robins said the crowd helped him to complete the London Marathon on Sunday after he suffered with cramps.
He finished the course in three hours, 19 minutes, but had to battle with cramp and the warm weather conditions during the race.
Stewart, a member of the Ryston Runners athletic club, said: “I struggled at 23 miles. I had to stop because I had severe cramps. It was so hot, but the crowds were really, really good.
“They told me to have my name printed on my vest and they would call your name to spur you on.”
Stewart said he did not have an initial fundraising target, but now expects to raise around £1,500 for the breast care unit at Lynn’s Queen Elizabeth Hospital.
His wife, Marie, is a breast care sister at the unit.