Friedrich Nietzsche, the philosopher thought to have died of syphilis, was the victim of a posthumous smear campaign by anti-Nazis, new research shows.

A study of medical records has found that, far from suffering a sexually transmitted disease that drove him mad, Nietzsche almost certainly died of brain cancer.

The doctor who carried out the study claims that the universally accepted story of Nietzsche having caught syphilis from prostitutes was concocted after World War II by Wilhelm Lange-Eichbaum, an academic who was one of Nietzsche's most vociferous critics. It was then adopted as fact by intellectuals who were keen to demolish the reputation of Nietzsche, whose idea of a "superman" was used to underpin Nazism.

The new research was done by Leonard Sax, the director of the Montgomery Centre for Research in Child Development in the United States. Dr Sax studied accounts of Nietzsche's collapse with dementia in 1889, when he was admitted to an asylum in Switzerland and initially diagnosed as being in the advanced stages of syphilis.

According to Dr Sax, however, Nietzsche's notes show no signs of the symptoms now regarded as evidence of this disease, such as an expressionless face and slurred speech.

"His facial expressions remained vivid, his reflexes were normal, tremor was not present, his handwriting after his collapse was at least as good as it had been in previous years - and his speech was fluent," Dr Sax said.

In the current issue of the Journal of Medical Biography, Dr Sax argues that the philosopher was suffering from a slowly developing brain tumour. This would account for Nietzsche's collapse and the migraines and visual disturbances he suffered.

In the decades following his death in 1900, Nietzsche's ideas of the Uebermensch - a new kind of human driven by the "will to power" - was adopted by the Nazis.

In a 1947 book Lange-Eichbaum alleged that a Berlin neurologist had once told him that the philosopher "had infected himself with syphilis in a Leipzig brothel during his time as a student there, and that he had been treated for syphilis by two Leipzig physicians".

The Telegraph, London