Manage blood sugar

The bigger effects reported in women, in people already diagnosed, and in Asian populations each rest on a handful of trials, few enough that ordinary chance could produce them. Doses and trial lengths varied widely, so 0.4 points is an average across regimens rather than the result of any one of them. Berberine caused more stomach and bowel upset than placebo in the large trial.

The 2025 review rated its own certainty very low on every outcome, because the experiments differed widely and most carried design weaknesses that could tilt a result either way. The older review's ranges were wide enough to hide a real effect: on body weight it ran from a 1.6kg loss to an 11.6kg gain. Not finding an effect is not the same as ruling one out.

A null result is not proof of equivalence. Eight small trials, with moderate inconsistency on three of the five outcomes, are underpowered to rule out a real difference between the two. No risk-of-bias assessment or certainty grading is reported.

Eight trials and 342 people in the metabolic pool, so a modest real effect could be missed. Participants were mostly healthy and not diabetic, which is the population least likely to show a metabolic improvement and leaves the question open in people who already have metabolic disease. Several pooled trials ran fourteen days, far too short for HbA1c, which reflects about three months of blood sugar, to move at all.

Both trials were funded by Novo Nordisk. Participants stayed on varying background diabetes medication, which is part of what separates the two groups rather than diabetes on its own. Gastrointestinal side effects reached 63.5% here against 34.3% on placebo.

Men only, all obese and insulin-resistant, so this does not describe healthy or older users, and twelve weeks is not years. The mitochondrial half is a sub-study of the same forty men rather than an independent replication, and the two count once. The trial did not report whether NAD actually rose in these participants, so a failure of delivery cannot be fully separated from a failure of the mechanism.

Twenty-five postmenopausal women with prediabetes who were overweight or obese, at a single site, for ten weeks. The endpoint is insulin sensitivity, a metabolic measure, not an ageing or longevity one. The senior authors hold NMN patent-licensing interests through their university. Later pooled analyses of the wider NMN literature found no metabolic effect, in populations that were mostly not metabolically ill.

Whether NMN improved insulin handling in a 25-person trial is disputed: the women given it began with less than half the liver fat of those on placebo, and liver fat is something NMN is meant to act on. A trial that size cannot settle it.

Genetic proxies for circulating levels are not a stand-in for swallowing a supplement, and neither study gave anyone one. Both draw on European-ancestry samples, and the UK Biobank cohort is healthier than the general population. Neither rules out a smaller effect running the other way.

Thirty-six people split between two drugs is small enough that an ordinary run of luck moves the number about as much as the drug does. With no placebo group, the fall also contains whatever three months of clinic visits and daily pill-taking do on their own. About a third of patients in the add-on arm had short-lived stomach upset.

Whether berberine lowers blood sugar is not the open question. The head-to-head with metformin everyone quotes came from a pilot with no placebo group, never built to size an effect, and no larger trial has repeated it.

This followed what people already consumed rather than assigning it, so the arrow could run the other way: someone watching their blood sugar has good reason to switch to sweeteners well before a diagnosis arrives. Intake came from participants' own repeated diet diaries. And these are the same participants and the same diaries behind the cancer finding, so the two results are not independent of each other.

The reviewers work for a consultancy that carries out safety assessments for industry clients, and the paper names no client. In the same passage where they set aside the studies reporting a glucose effect, they acknowledge that no long-term trial exists in people with pre-diabetes.

A one-dose glucose challenge and months of resting glucose measure different things, so both results can stand. What neither covers is years of glucosamine in someone who is already glucose intolerant.

Three people identified after the study began is a hypothesis rather than a finding, and the authors hedge their own conclusion accordingly. It was one dose alongside a 75 g glucose load, with no placebo group described. Larger reviews of fasting glucose over months and years find no such effect.

Oregano was one oil among several, so its own share cannot be told apart. The study was a pilot comparing three blends. No study of oregano taken with metformin or another diabetes drug has reported results.