Cognitive performance in molecular-hydrogen research

Evidence status M3: An endpoint is a pre-specified measure that is recorded and evaluated by a fixed rule. In cognitive research these are standardised test procedures with defined tasks, timings and scoring keys. A general impression, a remark in conversation or a self-assessment is not an endpoint in this sense. Anyone reading a study should therefore first check which endpoint was fixed before the study began. The wider frame is given by the overview where evidence levels for molecular hydrogen can be checked.

Evidence status M3: A study says something about the group it examined and about no other. Recruiting a clinically defined group yields statements for that group under the conditions of the protocol. Transferring them to people outside that group is a separate claim and needs a study of its own. What population limits look like in another research field is shown in population limits in metabolic research.

Evidence status H1 for the clinical part: Nishimaki et al. (2018), Current Alzheimer Research report a randomised clinical study in people with mild cognitive impairment. Limit: that is a clinically defined study population and not a setting with healthy adults; nothing follows from it for people outside that group, and no product link is established by it. Evidence status L2 for the animal-model part: the same publication additionally contains work in an animal model. Limit: animal models are not a human population, their findings are not transferable to people, and they are read here separately from the clinical part. How primary studies differ by design is set out in reading primary studies by design.

Evidence status M3: Test results change through repetition, expectation and daily form. Without a comparison group and without blinding, a difference cannot be assigned to any measure, because the same change can occur without it. The CONSORT statement: Schulz, Altman and Moher (2010), BMJ sets out which of these details a randomised study has to report. Limit: it is a reporting standard for study methodology and carries no statement about molecular hydrogen itself. What a different type of endpoint looks like is shown in comparing endpoints in sleep research.

Evidence status N: For healthy adults in everyday life, no suitable primary study with a defined cognitive endpoint is documented in this article. For comparison of endpoint types: Zanini et al. (2021), Experimental Gerontology recorded molecular and phenotypic markers in older adults over six months. Limit: markers are not cognitive endpoints, the age group was narrowly defined, and the work is drawn on here solely to distinguish endpoint types. Why an everyday term for self-reported complaints is not a study endpoint is set out in why brain fog is not a study endpoint.