Former US first lady Rosalynn Carter, the 95-year-old wife of former president Jimmy Carter, has dementia, the Carter family has announced.

"She continues to live happily at home with her husband, enjoying spring in Plains and visits with loved ones," the family said in a statement released by the Carter Center, referring to the couple's Georgia home.

Rosalynn Carter spent decades advocating to reduce the stigma associated with mental health issues, the family said, adding that it hoped sharing the news of her diagnosis would "increase important conversations at kitchen tables and in doctor's offices around the country."

"We do not expect to comment further and ask for understanding for our family and for everyone across the country serving in a caregiver role," the statement added.

The Carters occupied the White House during a Democratic administration from 1977 to 1981.

They have been married since 1946 and have four children.

Jimmy Carter has been receiving hospice care at home instead of medical intervention, the Carter Center said in February.

The 98-year-old Nobel Peace Prize laureate has lived longer after leaving the White House than any other president in US history.