No world celebrity of his stature has before publicly owned up to a dreadful disease that will inevitably cause the degeneration of his brain cells and loss of personality.
Almost certainly it would not have happened in Britain, where any form of mental disorder, curable or incurable, is still stigmatised, hidden and counted a matter of shame.
Here even physical illness in national leaders is viewed as personal weakness. Rumours abound that Lord Wilson of Rievaulx, who has taken little part in public life for years and none in the past nine months, has Alzheimer's. These are denied. An associate said last night that he was not well, but that his condition went back some 12 years. Lord Wilson's family was adamant that he did not suffer from Alzheimer's, he said.
Only passing mention of Alzheimer's disease is made in the obituary columns. The former footballer Danny Blanchflower died as a result of it nearly a year ago. Alex Lyon, the Labour MP for York between 1966 and 1983 who died in October last year, was also a sufferer. There would appear to be a consensus that the British public has little appetite for such intimacies. In America, all is different. The treatment for alcoholism of Betty Ford, wife of the former President, Gerald, became a matter of public congratulation.
Harry Cayton, director of the Alzheimer's Disease Society in Britain, described Mr Reagan's announcement as brave and welcome. His organisation seeks to destigmatise Alzheimer's and has been looking for a well-known sufferer who might be prepared to carry its banner.
He said: ``The disease has quite a different profile in the US. The reason for this is probably the very powerful lobby of older people and the pressure they are able to put on. It has resulted in a very high level of research being undertaken.
``There has never been such a stigma over mental diseases. Americans are much happier to talk about their psychological problems, their therapy, their marital break-ups. Here we are extremely reticent.''
Reagan's letter, page 13