“I just don’t think the science is there to support this, and it does have risk,” said Koepsell, an associate professor in the pathology and microbiology department at the University of Nebraska Medical Center. “Not to say that down the road it couldn’t lead to something, but it just seems premature.”

The use of blood products is an active area of aging research. Karmazin said work on what’s known as parabiosis in mice is the scientific basis for Ambrosia’s treatments.

In those studies, researchers who surgically joined the blood systems of young and old animals observed some positive effects on the health of aging mice.

But Dr. Thomas Rando, a Stanford University aging researcher who has conducted such studies, told the American Federation for Aging Research that there’s no evidence that blood donated from young people and given to older people has any health benefit.

“Until we have solid evidence that there really is a proven benefit in humans, I would not recommend to anyone that they receive any blood product based on the prospect that it might have some sort of ‘rejuvenating’ benefit,” he said in a Q&A with the aging research organization that was posted on its website. Other researchers in the field have made similar comments.