14,234 women.
Tested, not surveyed
In 2026, researchers at King’s College London published cognitive data on 14,234 women aged 45 to 55. The women in perimenopause were significantly more likely than premenopausal women to report cognitive symptoms, the brain fog and the memory problems. That part will not surprise you. You could have told them that.
Then the researchers stopped asking and started testing. Eight cognitive tasks. Objective performance differed minimally between the groups, and where there was a difference, the perimenopausal women were marginally more accurate than both the perimenopausal and the postmenopausal women.
They were not worse. If anything they were fractionally better. And this is not one outlier study. A 2025 systematic review and meta-analysis pooling the research on this question found no significant correlation between women’s subjective cognitive complaints during menopause and their measured performance across cognitive domains, apart from a small effect on learning efficiency. A separate analysis put it plainly: subjective complaints rise across the menopause transition while measurable performance shows little overall change.
Now stop reading it as a statistic and read it as a statement about you. The report is real. You are not imagining the feeling. The decline is what is missing. And the distance between those two things is where you have been living, possibly for years, without knowing it had a name or a size.