The Lancet doesn’t publish many papers on mental health but what it does do well is the coverage of global health issues (that is health issues not just related to North America, Europe and Australasia). The most recent example of this is a cohort study on the incidence and mortality of dementia in Cuba, the Dominion Republic, Venezuala, Peru, Mexico and China.
The authors hypothesized that because education and occupational attainment seem to protect against dementia, then in countries with elderly populations with limited education and who have done manual or unskilled work, that the incidence of dementia would be higher than in developed countries. They were able to follow up about two thirds of the original cohort of 13000 people over three to five years.
What they found was the incidence rate of dementia was about the same as in countries with higher incomes. This was most striking when they used a broader definition of dementia than the DSM IV which they found underestimated the true incidence of dementia in middle income countries. They also found that education and occupational attainment protected against dementia in middle income countries just as it does in high income countries.