Late last month Soviet leader Leonid Brezhnev, 72, abruptly canceled a state visit by French President Valéry Giscard d'Estaing, saying that he was ill. Although the Kremlin insisted it was only flu, there has long been speculation that the Communist party chairman is in quite poor health. According to Swiss physician Pierre Rentchnick, 56, Brezhnev is only one of many chiefs of state whose deteriorating physical condition may actually be influencing the course of world events. His book, Those Sick Who Govern Us, which recounts in detail the illnesses of 28 leading statesmen, was a French best-seller for 15 weeks and is being translated into 11 languages (although not yet into English). A specialist in infectious diseases and a member of the New York Academy of Sciences, Rentchnick was born and educated in Geneva, where he is associate professor at the University of Geneva and chief editor of the weekly journal Medicine and Hygiene. He recently diagnosed the health of some world leaders, past and present, for Helga Chudacoff of PEOPLE.

What is the most striking example of a sick leader making decisions of worldwide importance?

Undoubtedly Franklin D. Roosevelt at the Yalta Conference in February 1945. The President was close to death and in fact died two months after the conference. However, before the fatal hemorrhage in his brain, he had a lot of minor hemorrhages and experienced changes in mood and concentration.

How did his health show at Yalta?

Churchill noticed that the President arrived looking "frail and ill." En route he failed to read the files prepared by the State Department. During the conference, Roosevelt napped frequently. Lord Moran, Churchill's doctor, said that the President "has all the symptoms of hardening of the arteries of the brain in an advanced stage." FDR's adviser, Harry Hopkins, was so sick that he was unable to attend many of the meetings and dinners.

How did this affect FDR's judgment?

It was a bad decision for Roosevelt to agree to preside at the conference. Averell Harriman, who was present, said that FDR "didn't have the strength to be quite as stubborn as he liked to be. But I can't believe that it would have made a great difference on, say, Poland. The Red Army was in full control of the country and no amount of careful drafting could have changed that."

Do American Presidents always get the best medical advice?

Not necessarily. I think it is a mistake to pick a doctor from the military services. For instance, FDR's physician, Vice-Admiral Ross T. McIntire, was an ear, nose and throat specialist. When I spoke to him, he denied everything about Roosevelt's diseases. He dismissed the diagnosis of high blood pressure and heart disease, and insisted it was just flu.

Did Stalin fare any better?

I talked to Dr. Alexander Myasnikov, a good heart specialist and one of Stalin's 10 doctors. Remember, if you are one of 10, you have to compromise. Leaders are not the best patients in the world and do not always receive the best treatment and advice because doctors sometimes are afraid to tell them the truth. Now, in Stalin's particular case, he was told about his high blood pressure. He was advised to cut down on alcohol, tobacco and coffee, which Stalin did not do. He, too, died of a brain hemorrhage.

President Kennedy's back problems were well known. Did he take medications for his pains which might have affected his alertness?

He used painkillers but—and this is more serious—he had to take cortisone for Addison's disease, a severe sickness of the adrenal glands. At that time cortisone was not as pure as it is today. It produced a wide range of physical side effects.

How might Jimmy Carter be affected by his hemorrhoid problem?

If the problem is chronic, people know how to manage and what to do. They are not affected. If the hemorrhoids are acute, though, they can produce a very depressive state because the disease is unesthetic and painful. But a doctor can ease the pain in a day or two. Just to be sure that hemorrhoids are not masking the beginning of cancer, the doctor should insist on a rectoscopy.

What exactly did French President Pompidou die of while still in office in 1974?

Three of my colleagues were treating him, and I knew they kept the truth from the public. Pompidou was said officially to have the grippe and later hemorrhoids. He in fact suffered a rare blood disease called the Waldenström syndrome. It is a slow, deadly sickness and is treated with cortisone. He ultimately died from the complications that resulted from this disease.

What do you know about Yugoslav President Tito's health?

I met Tito's physician in 1975 when he came to Geneva to study the emergency unit I had organized, the Cardiomobile. He told me that Tito had had a heart attack in 1970 and that when he was called to take care of him, he had to sign a paper not to leave Yugoslavia for five years and not to speak about Tito's disease.

How is Tito's health now?

His brain was marvelous for a long time, but he is suffering from high blood pressure and has had two heart attacks. When he goes on a trip there is always a Cardiomobile following with everything thinkable in case of another attack. He might have only one or two hours of concentration a day. But he is a symbol of power, like another Communist leader, Brezhnev.

How ill is Leonid Brezhnev?

He has high blood pressure and, I believe, has had six or seven heart attacks—this in addition to arteriosclerosis of the brain and Alvarez disease or a series of "little strokes." We are not certain if Brezhnev is wearing a pacemaker; we just know that around the time of one of his illnesses the most important French manufacturer of pacemakers was called to Moscow. Earlier this month three West European specialists in arteriosclerosis were summoned. Brezhnev is a very sick man.

How well can Brezhnev function?

He is able to read a report of three or four pages, and you may be able to talk to him for as much as three hours—I know this from patients with the same disease. But if you suddenly ask a specific question, you realize that these people may look well but in conversation have simply turned off.

Israel's Prime Minister Menachem Begin admits to three heart attacks. What is your view of his health?

Begin knows he has a serious heart disease. I recall what he said at Camp David to Sadat, who's also had heart trouble: "We have to move a little faster because both of us have reason to fear another heart attack."

Was Golda Meir strong physically during her tenure?

Not at all. Golda Meir was very sick, even before she became prime minister. She had a type of Hodgkin's disease, a lymphoma requiring aggressive treatment like chemotherapy, which makes patients very tired. As prime minister she was responsible for the strange state of not being sufficiently prepared for the 1973 Yom Kippur War.

Obviously, Adolf Hitler had mental problems. What about his physical health?

Just after the beginning of the Russian campaign in June 1941, Hitler started showing symptoms of Parkinson's disease. In the next three years, a period that includes the disastrous siege of Stalingrad, he had both hepatitis and a heart attack. During this time Hitler's generals did not understand his decisions because they did not know about his illnesses.

Winston Churchill has been described in a British medical journal as suffering "impaired judgment" because of drugs given him for his health. What about that?

Churchill had more problems with alcohol than with drugs. During the war he had manic depressive moods. So in order to avoid depression, he became overactive and drank too much. The second stage of his life was rather sad. Although he had been very sick with brain apoplexy, he again became head of the British government. He would not resign. The Churchill family asked his doctor to advise him to do so, but the doctor refused. He felt his patient would then fall into deep depression.

Has a powerful politician ever resigned, although he did not have to?

De Gaulle did. While he was not so sick that it endangered his leadership of France, he was feeling the problems of old age. While he was president, he had a prostate operation and asked the doctors to tell the truth to the public. There is still debate as to whether he was showing signs of mental weakness when he visited Canada and behaved rather strangely, asking for the separation of Quebec and canceling his official visit to the prime minister.

What could be done to keep sick chiefs of state out of office?

There is a special relationship between a doctor and his patient. That's why these important politicians should not be examined by their own physicians but instead by other renowned doctors who are not interested in politics. I will go one step further: They should also be examined by doctors of the opposition party. Then, perhaps, we would be near objectivity.