Veikko Vennamo, claimed that he remained President so long mainly because he and his closest associates were power-hungry. In 1980 Kekkonen was awarded the Lenin Peace Prize. Later life From December 1980 onwards, Kekkonen suffered from an undisclosed disease that appeared to affect his brain functions, sometimes leading to delusional thoughts. He had begun to suffer occasional brief memory lapses as early as the autumn of 1972; they became more frequent during the late 1970s. Around the same time, Kekkonen's eyesight deteriorated so much that for his last few years in office, all of his official papers had to be typed in block letters. Kekkonen had also suffered from a failing sense of balance since the mid-1970s and from enlargement of his prostate gland since 1974. He was also subject to occasional violent headaches and suffered from diabetes from the autumn of 1979. Rumors about his declining health had begun to circulate in the mid to late 1970s, but the press attempted to silence these rumors to respect the president's privacy. According to biographer Juhani Suomi, Kekkonen gave no thought to resigning until his physical condition began to deteriorate in July 1981. The 80-year-old president then began to seriously consider resigning, most likely in early 1982. Prime Minister Mauno Koivisto finally dealt a defeat to Kekkonen in 1981. In April, Koivisto did what no one else had dared to during Kekkonen's presidency by stating that under the constitution, the prime minister and cabinet were responsible to Parliament, not to the President. Kekkonen asked Koivisto to resign, but he refused. This is generally seen as the death knell of the Kekkonen era; Kekkonen, who felt that he had lost a significant amount of his authority, never fully recovered from the shock caused by this event. Historians and journalists debate the precise meaning of this dispute. According to Seppo Zetterberg, Allan Tiitta, and Pekka Hyvärinen, Kekkonen wanted to force Koivisto to resign to decrease his chances of succeeding him as president. In contrast, Juhani Suomi believed the dispute involved scheming between Koivisto and rival prospective presidential candidates. Kekkonen at times criticised Koivisto for making political decisions too slowly and for his vacillation, especially for speaking too unclearly and philosophically. Kekkonen became ill in August during a fishing trip to Iceland. He went on medical leave on 10 September, before finally resigning due to ill health on 26 October 1981, aged 81. There