Local media subsequently reported that he was “exhausted and disheartened” after years of leading the government.
Prayut said on Thursday that he had made light-hearted remarks to reporters on Wednesday because he was “in a good mood”.
During an informal interview with reporters after a press conference on Wednesday, he told them he had lost five kilogrammes and had difficulty eating and sleeping since the election campaigning began.
Prayut is the top prime ministerial candidate of the United Thai Nation Party.
Wednesday’s press conference was held at the party’s headquarters.
On Thursday he responded to headlines based on the statements, saying: “I am not disheartened. I am still strong and not old.”
“Don’t you think I am boasting,” he told reporters.
Prayut visited the Royal Thai Police headquarters on Thursday to chair meetings of the National Police Policy Board and the Police Commission.
He asked the public to offer moral support to police officers devoted to their work.
“We have to praise good officers to give them encouragement so that they continue serving us,” he said.
“The police have been blamed so much that the organisation has been badly damaged,” he added.