What This Trial Looked At
One of the earliest controlled human trials of hydrogen-rich water for metabolic health was conducted in 2008 by Kajiyama and colleagues at the Kajiyama Clinic and Kyoto Prefectural University of Medicine. The team set out to test a focused question: can drinking water that has been infused with molecular hydrogen actually improve the lipid and glucose markers that define type 2 diabetes?
The study was a randomised, double-blind, placebo-controlled crossover trial — the strongest design available for testing a single intervention against placebo. The researchers recruited 36 participants: 30 with diet- and exercise-controlled type 2 diabetes mellitus, and 6 with impaired glucose tolerance (a pre-diabetic state). Each participant drank 900 mL per day of either hydrogen-rich pure water or placebo pure water for 8 weeks, with a 12-week washout period between conditions.
What They Found
Hydrogen-rich water intake was associated with measurable improvements in several of the markers most closely linked to cardiovascular risk in diabetes. Modified LDL cholesterol — the form of LDL that has been oxidatively damaged and is most strongly implicated in plaque formation — fell by 15.5 percent (P < .01). Small dense LDL, another particularly atherogenic LDL subclass, dropped by 5.7 percent (P < .05). And urinary 8-isoprostanes, a sensitive marker of systemic oxidative stress, decreased by 6.6 percent (P < .05).
Beyond these statistically significant changes, the trial observed positive trends in oxidised LDL, free fatty acids, adiponectin, and extracellular-superoxide dismutase — all measures that broadly indicate a more favourable metabolic and oxidative-defence profile.
The most striking finding came from the subset of participants with impaired glucose tolerance: in 4 of 6 of them, the oral glucose tolerance test — the standard clinical test for diagnosing pre-diabetes and diabetes — normalised after the hydrogen-water period.
What This Means in Context
This is a small, early trial — the kind of study that opens a question rather than settles it. The sample of 36 is modest, the duration of 8 weeks is short relative to how diabetes evolves, and the work has not been replicated at the same scale in independent multicentre trials. The strongest signal — the normalisation of glucose tolerance in four of six patients with impaired glucose tolerance — comes from a subgroup of just six people.
What the trial does establish is a coherent mechanistic story: hydrogen-rich water did the kinds of things hydrogen has been hypothesised to do in laboratory work — reducing oxidative damage to LDL particles, lowering systemic oxidative-stress markers, and trending favourably across a panel of metabolic indicators. As a proof-of-concept study it has earned its place as one of the foundational clinical references in the molecular-hydrogen literature, and has informed the design of larger trials that followed.
What It Means for You
If you are managing type 2 diabetes or are concerned about pre-diabetes, the take-away from this trial is that drinking hydrogen-rich water alongside the basics — diet, exercise, and any medication your doctor has prescribed — produced measurable improvements in lipid and oxidative-stress markers in a randomised, placebo-controlled setting. The trial does not establish hydrogen-rich water as a treatment for diabetes, and it is not a substitute for the standard care your doctor recommends. As with any complementary approach, talk to your treating physician before making changes to your routine.
Citation: Kajiyama, S., Hasegawa, G., Asano, M., Hosoda, H., Fukui, M., Nakamura, N., Kitawaki, J., Imai, S., Nakano, K., Ohta, M., Adachi, T., Obayashi, H., & Yoshikawa, T. (2008). Supplementation of hydrogen-rich water improves lipid and glucose metabolism in patients with type 2 diabetes or impaired glucose tolerance. Nutrition Research, 28(3), 137–143. PubMed
