The article shows how caffeine can affect the brain, having a direct impact on brain fog. The article cites Vail Health, which suggests that brain fog is caused by poor sleep or fluctuation in blood sugar. Caffeine can impact sleep, but it's not the sole cause of brain fog, as other factors can also affect brain function. The original article was written by a professor from the University of Maryland, and it was reviewed by a registered dietitian. Both individuals are highly qualified, which makes the article more credible. The sources that are cited, Vail Health and Cleveland Clinic, are well-respected organizations. While caffeine might not directly cause brain fog, it can cause dehydration and bad sleep, which do cause brain fog. Not all brain fog is linked to caffeine; consumption can increase the chances of experiencing brain fog due to its non-direct effects. So I would say this fact check is true.