Dr. David Owen, a doctor and member of the House of Lords, says millions of people are affected by the decisions of people in high public office, so leaders have an obligation to the public to ensure that their decision making is not impaired by physical or mental illness.

Many heads of government and their personal doctors do not tell the truth about their illness and have received inferior medical treatment as a result of this secrecy, Owen wrote in the British Medical Journal.

For example, when Francois Mitterrand was president of France he kept his cancer of the prostate secret for 11 years, even though his personal doctor made monthly public statements about his health with no mention of his true medical condition, Owen said.

When in office, leaders should be obliged to have an annual independent health check to ensure that they are fit for office and should step down -- temporarily or permanently -- if their illness is affecting their capacity to do the job, Owen suggested.