Evidence gap map: what has been studied, in whom, how well
One table: every health-condition tag with at least 20 studies in the database (55 tags), by the kind of evidence behind it, from systematic reviews down to reviews that report no new data. Darker cells hold more studies. The last two columns show how the human studies came out and, where we have written a reviewed hub introduction, how certain the evidence is. Figures as of November 4, 2026; the prose was last reviewed on November 3, 2026.
How to read it
- A row with many animal and laboratory studies and nothing in the SR/MA, RCT or other-human columns is a gap: a topic where no one has yet tested hydrogen in people.
- A row whose human studies sit in the "other human" column has been studied in people, but without randomization; those studies cannot show cause and effect.
- "Human results +/−" counts human studies with a positive recorded result against those with a neutral, negative or mixed one. A high positive share with few studies says more about publishing than about hydrogen — see the limits of the evidence.
- "Certainty" is the GRADE-style grade from the hub introduction, where one exists; "not graded" means no reviewed introduction has been written for that tag yet.
- Tags are assigned per study and a study can carry several, so rows overlap; columns within a row do not.
The biggest gaps
11 of the 55 tags have no human study at all. The ones with the most animal work and still nothing in people:
- Sepsis: 76 animal studies, 0 in people
- Acute Lung Injury: 56 animal studies, 0 in people
- Acute Kidney Injury: 30 animal studies, 0 in people
- Sepsis-Associated Encephalopathy: 21 animal studies, 0 in people
28 tags have at least one randomized controlled trial; 19 have two or more.
The map
Shading: 1–2 3–9 10–29 30+ studies.
| Condition tag | All | SR/MA | RCT | Other human | Animal | Lab | Review | Human results +/− | Certainty |
|---|---|---|---|---|---|---|---|---|---|
| Oxidative Stress | 214 | 2 | 12 | 16 | 58 | 64 | 39 | 28 / 4 | not graded |
| Cancer | 127 | 1 | – | 3 | 12 | 33 | 71 | 3 / 0 | not graded |
| Cardiovascular Disease | 115 | 3 | 4 | 7 | 36 | 8 | 41 | 11 / 0 | not graded |
| Ischemia-Reperfusion Injury | 114 | – | 2 | 2 | 70 | 4 | 29 | 2 / 2 | not graded |
| Sepsis | 101 | – | – | – | 76 | 8 | 12 | – | not graded |
| Stroke | 76 | – | 2 | 3 | 33 | 5 | 31 | 4 / 0 | not graded |
| Metabolic Syndrome | 74 | 3 | 6 | 12 | 23 | 4 | 19 | 21 / 0 | not graded |
| Type 2 Diabetes | 69 | 1 | 6 | 14 | 21 | 5 | 18 | 20 / 0 | Very low |
| Acute Lung Injury | 65 | – | – | – | 56 | 1 | 4 | – | not graded |
| Brain Injury | 63 | – | – | 2 | 48 | 4 | 7 | 2 / 0 | not graded |
| Oxidative Stress Disorders | 63 | 1 | – | – | 7 | 6 | 46 | – | not graded |
| Parkinson's Disease | 50 | – | 5 | 2 | 12 | 4 | 23 | 4 / 3 | not graded |
| Neuroinflammation | 48 | – | – | 2 | 40 | 2 | 3 | 2 / 0 | not graded |
| Traumatic Brain Injury | 47 | – | – | 1 | 28 | 1 | 17 | 1 / 0 | not graded |
| Obesity | 46 | 1 | 6 | 4 | 17 | 2 | 11 | 12 / 0 | not graded |
| Chronic Kidney Disease | 45 | – | – | 13 | 20 | 2 | 9 | 13 / 0 | not graded |
| Metabolic Disorders | 38 | 1 | 1 | – | 4 | 6 | 22 | 1 / 0 | not graded |
| COVID-19 | 36 | 1 | 3 | 7 | – | 2 | 22 | 8 / 1 | not graded |
| Inflammatory Diseases | 36 | 1 | – | – | 4 | 7 | 21 | – | not graded |
| Acute Kidney Injury | 35 | – | – | – | 30 | 1 | 4 | – | not graded |
| Alzheimer's Disease | 35 | – | – | 5 | 8 | 2 | 17 | 5 / 0 | not graded |
| Cognitive Impairment | 35 | – | 2 | 2 | 28 | – | 2 | 4 / 0 | not graded |
| Cardiac Arrest | 34 | 1 | 4 | 3 | 16 | – | 8 | 5 / 1 | not graded |
| Neurodegenerative Diseases | 34 | – | – | – | 5 | 7 | 22 | – | not graded |
| Inflammatory Bowel Disease | 33 | – | 1 | – | 15 | 3 | 12 | 1 / 0 | not graded |
| Atherosclerosis | 32 | – | 1 | 1 | 14 | 3 | 12 | 2 / 0 | not graded |
| Cerebral Ischemia | 32 | – | – | 2 | 23 | 2 | 5 | 2 / 0 | not graded |
| Inflammatory Conditions | 30 | – | – | – | 1 | 1 | 23 | – | not graded |
| Mitochondrial Dysfunction | 30 | – | – | – | 8 | 8 | 10 | – | not graded |
| End-Stage Renal Disease | 28 | – | – | 14 | 8 | 2 | 4 | 14 / 0 | not graded |
| Chronic Wounds | 27 | 1 | 1 | 4 | 11 | 7 | 2 | 5 / 0 | not graded |
| Heart Attack | 27 | – | – | – | 18 | 3 | 6 | – | not graded |
| Chronic Inflammation | 26 | – | – | 6 | 3 | 5 | 7 | 7 / 0 | not graded |
| Ischemic Stroke | 26 | – | 1 | 1 | 16 | 1 | 7 | 2 / 0 | not graded |
| Gut Dysbiosis | 25 | – | – | 2 | 9 | 6 | 3 | 2 / 0 | not graded |
| Myocardial Infarction | 25 | – | – | – | 18 | 1 | 6 | – | not graded |
| Subarachnoid Hemorrhage | 25 | – | 2 | 1 | 16 | – | 5 | 2 / 0 | not graded |
| Type 1 Diabetes | 25 | 1 | – | 3 | 14 | 3 | 3 | 3 / 0 | not graded |
| Hypertension | 23 | – | 1 | 5 | 12 | – | 3 | 6 / 0 | not graded |
| Periodontal Disease | 23 | 1 | 1 | 1 | 7 | 9 | 3 | 1 / 1 | not graded |
| Sepsis-Associated Encephalopathy | 23 | – | – | – | 21 | – | 2 | – | not graded |
| Birth Asphyxia | 22 | – | – | 1 | 19 | – | 2 | 1 / 0 | not graded |
| Depression | 22 | – | 2 | 2 | 14 | – | 3 | 4 / 0 | not graded |
| Dyslipidemia | 22 | 3 | 2 | 3 | 9 | – | 2 | 8 / 0 | not graded |
| Liver Disease | 22 | 3 | 2 | – | 12 | – | 5 | 1 / 1 | not graded |
| Rheumatoid Arthritis | 22 | 1 | 1 | 6 | 6 | 3 | 4 | 7 / 0 | not graded |
| Heart Failure | 21 | – | – | 1 | 14 | – | 3 | 1 / 0 | not graded |
| Acute Respiratory Distress Syndrome | 20 | – | – | – | 14 | 2 | 3 | – | not graded |
| Cognitive Dysfunction | 20 | – | 1 | – | 18 | – | 1 | 1 / 0 | not graded |
| Diabetes | 20 | – | – | – | 6 | 5 | 9 | – | not graded |
| Endothelial Dysfunction | 20 | – | 3 | – | 6 | 8 | 1 | 3 / 0 | not graded |
| Hypoxic-Ischemic Encephalopathy | 20 | – | – | 1 | 16 | – | 3 | 1 / 0 | not graded |
| Insulin Resistance | 20 | – | 2 | 4 | 8 | 3 | 2 | 7 / 0 | not graded |
| Metabolic Dysfunction | 20 | – | 4 | 3 | 6 | 1 | 4 | 7 / 0 | not graded |
| Pulmonary Fibrosis | 20 | – | 2 | 2 | 11 | 2 | 3 | 4 / 0 | not graded |
Reuse
The table is built from the open dataset (CC BY 4.0) each time the page is built, so anyone can recompute or extend it. An embeddable version of the table is at /evidence-gap-map/embed; it carries a link back here. Design classes and tags are machine-drafted and audited (methodology); report a misclassified study via contact.