NEW YORK – Cars need oil changes to keep their engines running smoothly.

Some anti-ageing influencers, along with a handful of scientists, believe exchanging the plasma in your blood can do a similar thing for humans to help slow biological ageing. The procedure is offered for thousands of dollars a session at many longevity clinics.

In a car, “you change the oil every 3,000 miles because it clears out debris”, said president and chief executive Eric Verdin of the Buck Institute for Research on Aging. Your blood, he said, can also accumulate potentially damaging particles that can be flushed out.

One of the first trials examining plasma exchange for anti-ageing in humans, published recently in the journal Aging Cell, offers early evidence that it may be able to slow the biological breakdown that comes with age, even in otherwise healthy people.

The small study of 42 participants, with an average age of 65, found that those who got plasma exchange therapy over the course of a few months had lower concentrations in their blood of the biological compounds that accumulate with age, compared with a control group.

The trial was sponsored by Circulate Health, a plasma exchange start-up, and co-authored by Dr Verdin, a company co-founder and head of the scientific advisory board.

Still, other scientists who study plasma exchange are sceptical. Its anti-ageing benefits for healthy people have never been proven in large clinical trials, said Dr Katayoun Fomani, an associate professor and medical director of the blood bank at the University of Alabama at Birmingham. And drawing blood and replacing plasma with added fluids could put patients at risk for unnecessary medical complications without a clear payoff.

How the procedure works

Plasma exchange is an established treatment for some blood disorders, autoimmune diseases and neurological conditions, and it is typically covered by insurance when deemed medically necessary. It is not covered for anti-ageing purposes.

During the therapy, a provider – typically a registered nurse or a technician – hooks the patient up to a machine that draws out blood. The machine separates and discards the plasma from the blood, replaces it with donor plasma or a substitute fluid, then returns the blood back to the patient.

The substitute fluid often contains a mixture of saline and proteins, like albumin. In some cases, an infusion of antibodies or drugs may also be added to boost the immune system or fight certain diseases. Each sess...