It was an elegant hypothesis, the kind that makes biologists lean forward. Parkinson’s disease involves failing cellular energy systems; NAD is one of the molecules those systems run on; a supplement called nicotinamide riboside can raise NAD levels. A rigorous yearlong trial has now tested whether that chain of reasoning helps patients — and, as published in JAMA, it found no clinical benefit.
Negative results rarely make headlines, and this one deserves better. The trial followed patients taking the NAD-boosting supplement over a full year, long enough for the hoped-for effect to show itself in the measures that matter to people living with Parkinson’s. It did not. Professor Tzoulis and the team behind the study reported the outcome plainly, which is precisely what makes it valuable: a hypothesis the supplement industry has monetised for years has now met a controlled test of meaningful duration, and lost.
The commercial backdrop is unavoidable. NAD boosters are sold directly to consumers — often with Parkinson’s-adjacent marketing language, celebrity wellness endorsements and price tags calibrated to hope. Patients, facing a disease with no disease-modifying treatment, are the most motivated buyers in medicine. A yearlong null result in a major journal does not ban the products, but it does arm neurologists with an answer when patients ask the question in clinic: we tested that, carefully, for a year.
The science underneath is not thereby closed. NAD biology remains central to research on ageing and neurodegeneration, and a failed supplement trial tests one molecule, one dose and one population — not the whole pathway. Researchers, Tzoulis among them, have been careful to separate the pathway’s promise from the product’s performance, and further work on related compounds continues on exactly that distinction.
What the trial changes immediately is the information balance. Until now, the burden of proof in the NAD aisle sat with sceptics. JAMA has moved it. In a field where hope is the most prescribed substance of all, a well-run negative trial is not a disappointment. It is a public service with a DOI number.
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