Previous studies in The States showed that Black Americans are roughly 1.5 to 2 times as likely than whites to develop Alzheimer’s and related dementias. 

In September 2022 - University College London released their findings on ethnicity v dementia - more here

While UCL's study did not review the reasons for differences in dementia incidence between groups, the researchers point to prior evidence that black people may be more likely to develop dementia due to higher prevalence of dementia risk factors such as hypertension, diabetes, and obesity.

Whilst these may well be contributory factors, newer research (March 2023) links Vitamin D deficiency with incident dementia.

Scientific fact:- the darker the skin colour, the higher concentration of mellanin, the lower the natural production of vitamin D (why?).

Conclusion:- (from this article) - lack of vitamin D could well be a contributory factor in dementia development

Conclusion 2:- 50 years ago, right across the board, did a black man get the same educational stimuli as a white man?