People magazine, in its 5 December edition, said that Reagan, 92, spends his days confined to a hospital bed in his Los Angeles mansion under the intense care of his wife, Nancy.
And the emotional and physical strain is taking a heavy toll on his increasingly-frail wife, 82, who fiercely protects her ailing husband's dignity and even bars his closest friends from seeing him.
Reagan's formerly estranged step-daughter Patti Davis wrote in the magazine that it is only her physically robust father's strength that is keeping him alive.
"I think it's the tenacity of his soul - he just isn't ready to leave his reunited family," she says.
The former Republican leader announced he was suffering from the debilitating neural disease in 1994.
Former Hollywood star
Patty Reagan said she is often asked whether her father recognises her as the president's entourage keeps a tight lid on details of his illness.
"It makes me realise that my mother and I have been so protective of his condition since he became ill - almost a decade now - that it has allowed people to imagine he is still talking, still walking, still able to stumble into a moment of clarity," she wrote.
"But it would be a disservice to every family who has an Alzheimer's victim in their embrace to say any of that is true, and I don't believe my father would want us to lie."
Reagan's office in Los Angeles declined to comment on the report, but said the former president was "the same" as ever.
Nancy Reagan, who, like her husband of more than 50 years, is a former Hollywood star, has appeared frailer in recent years and now limits her public appearances to events associated with Reagan's political legacy.