Nutrition and the prevalence of dementia in mainland China, Hong Kong, and Taiwan: an ecological study.

BACKGROUND Western diets are associated with obesity, vascular diseases, and metabolic syndrome and might increase dementia risk in later life. If these associations are causal, those low- and middle-income countries experiencing major changes in diet might also see an increasing prevalence of dementia. OBJECTIVE To investigate the relationship of dietary supply and the prevalence of dementia in mainland China, Hong Kong, and Taiwan over time using existing data and taking diagnostic criteria into account. METHODS Estimated total energy supply and animal fat from the United Nations was linked to the 70 prevalence studies in mainland China, Hong Kong, and Taiwan from 1980 to 2012 according to the current, 10 years, and 20 years before starting year of investigation. Studies using newer and older diagnostic criteria were separated into two groups. Spearman's rank correlation was calculated to investigate whether trends in total energy, animal fat supply, and prevalence of dementia were monotonically related. RESULTS The supply of total energy and animal fat per capita per day in China increased considerably over the last 50 years. The original positive relationship of dietary supply and dementia prevalence disappeared after stratifying by newer and older diagnostic criteria and there was no clear time lag effect. CONCLUSION Taking diagnostic criteria into account, there is no cross-sectional or time lag relationship between the dietary trends and changes in dementia prevalence. It may be too early to detect any such changes because current cohorts of older people did not experience these dietary changes in their early to mid-life.