"We ruled it Alzheimer's disease as the cause of death with other significant contributing factors," John Fudenberg, the coroner in Clark County, Nevada, told CNN on Monday.
Those contributing factors include coronary artery atherosclerosis, type 2 diabetes, hypertension, coronary heart disease and cerebrovascular disease.
Fudenberg said the investigation into the 89-year-old King's death is now closed.
Soon after King died May 14 in home hospice care in Las Vegas, two of his 11 adult children alleged he was poisoned to death by his closest associates. The daughters said two of King's associates gave him medication to induce diabetic shock.
Preliminary autopsy results at the time didn't support the contention.
King's daughters, Patty King and Karen Williams, made the accusations in separate, but identically worded, affidavits
"I believe my father was poisoned and that he was administered foreign substances to induce his premature death," they said in their affidavits. "I believe my father was murdered."
Both women accused LaVerne Toney, King's business manager, and Myron Johnson, his personal assistant, of neglect.
At the time, an attorney for Toney said the daughters were chasing a check.
"This is absolutely about money," Eric Brent Bryson told CNN, adding the charges were "absolutely ridiculous" and "unfounded."
Late Monday night, CNN was unable to reach the lawyers for the daughters or King's associates.
The allegations were the latest salvo in a bid by some of King's children to wrest control of the late singer's assets, believed to be in the millions.
King had 15 children from several different relationships. Eleven children are still living.
Earlier this year, Patty King, Karen Williams and a third daughter, Rita Washington, went to court, accusing Toney -- the business manager -- of elder abuse and neglect. But a judge tossed out the case, for lack of evidence.