Who Might Benefit? Populations, Tasks, and the Limits of Generalization
The reported cognitive effects of creatine monohydrate do not appear as one uniform response across every participant and every test. This chapter asks where the 2024 review found signals in attention time and processing-speed time, where it did not, and how far those subgroup patterns can reasonably travel. The goal is to distinguish conditional evidence from personalized advice.
Where the reported signals appeared
The overall attention-time result in the 2024 review was already a conditional kind of outcome: it concerned the time required to complete selected attention tasks, not every aspect of attention. The subgroup analyses narrowed it further. When the studies were grouped by health status, the reported effect was significant among participants with illnesses but not among healthy participants. When they were grouped by age, the effect was significant among adults aged 18–60 but not among participants over 60.
The reported numbers show why context matters. For participants with illnesses, the attention-time standardized mean difference was −0.52, with a 95% confidence interval from −0.96 to −0.08. For adults aged 18–60, it was −0.55, with a 95% confidence interval from −0.90 to −0.21. A negative value represents less time to finish the task in this analysis. It does not mean that creatine reduced attention. It means the intervention and control groups differed in the time outcome in the direction the authors interpreted as faster completion.
Those comparisons should not be read as a simple ranking of people. The studies involving illness may differ from healthy-adult studies in more than one way: the participants’ baseline condition, the type of task, the surrounding treatment, and the reason the trial was conducted may all vary. Similarly, adults aged 18–60 and adults over 60 are not defined only by a number. They may differ in health, baseline cognitive performance, diet, and the amount of evidence available for each group. A subgroup result can identify a pattern in the collected studies without isolating the cause of that pattern.
Processing speed showed a different subgroup contrast. The overall processing-speed-time result was reported as significant, but the effect was significant among female participants and not among male participants. In the female subgroup, the standardized mean difference was −0.87, with a 95% confidence interval from −1.53 to −0.21. As with attention time, the endpoint is completion time. The result does not show that every component of processing speed improved, and it does not establish that sex alone caused the difference between subgroup estimates.
A subgroup comparison is strongest when it is planned, well powered, and supported by a plausible explanation that survives replication. The material provided here does not supply that level of confirmation. The 2024 paper itself notes the limited number of studies, heterogeneity in design and testing, and restricted evidence for older adults and particular clinical populations. The female processing-speed result is therefore a useful signal for further research, not a screening test for who should use creatine.