Former first lady Nancy Reagan says that five years after her husband was diagnosed with Alzheimer's disease, he no longer is capable of having a conversation that makes sense.

Reagan also said that friends of former president Ronald Reagan no longer are invited to their California home because he does not recognize them. The 88-year-old former president no longer swims or takes walks, she said.

She commented during a recent conversation with C-SPAN executive Brian Lamb at the Ronald Reagan Presidential Library in Simi Valley, Calif. The session was part of the cable network's series "American Presidents: Life Portraits."

In the interview, Nancy Reagan explained how the former president, without assistance, wrote his own letter to the American people in 1994 disclosing he had been diagnosed with Alzheimer's disease, a progressive condition in which the brain degenerates, causing severe memory loss and dementia.

She was asked what she has learned about the disease over the past five years.

"That it is probably the worst disease you can ever have," she replied. "Because you lose contact and you're not able to share. In our case, to share all of those wonderful memories that we have."

"Can you have a conversation with the president that makes sense to you?" Lamb asked.

"Not now, no," Reagan replied.

"How have you dealt with it when people come to visit and he doesn't recognize them," he asked.

"Well, now we don't have visitors. . . . We never let that happen," she said.

Alzheimer's is the fourth leading cause of death among adult Americans. An estimated 4 million Americans have the disease.

Reagan said her husband's public acknowledgment helped lift the stigma many people associated with Alzheimer's.

"They didn't know it was a disease, like any other disease," she said. "He helped dispel that. And now it is amazing how many people come up and say to me that their mothers and fathers and husbands and somebody in their family has Alzheimer's. Now they're free to talk about it. So he did a great thing."

Reagan was asked how she has learned to deal with her husband's condition.

"You just do it; you just get up and take each day as it comes and put one foot in front of the other," she replied. "You just love."