The Japan Public Health Center-based prospective (JPHC) Study is a large population-based cohort. Midlife dietary intake was assessed on two occasions: in the years 1995 and 2000 (aged 45-64 in 1995). In 2014-2015, approximately 1300 participants from Saku district in Nagano prefecture completed a mental health screening including later life depression and cognitive decline (i.e., mild cognitive impairment (MCI) and dementia). We used logistic regression analyses to calculate odds ratios (ORs) for MCI and dementia. Based on this survey, we found the following characteristics of midlife diet, which may be useful information to prevent cognitive decline/dementia.

1. 1. High-density lipoprotein cholesterol (HDL-C) and later cognitive decline (Svensson et al. Transl Psychiatry, 2019): Midlife high-density lipoprotein cholesterol (HDL-C) is a measure which could help identify individuals at reduced risk of developing age-related cognitive decline. Compared to the lowest HDL-C quartile, the highest HDL-C quartile was significantly inversely associated with MCI. High HDL-C (quartiles 2-4) was inversely associated with dementia compared to low HDL-C (quartile 1).

2. 2. Dietary fish and n-3 polyunsaturated fatty acid (PUFA) and later cognitive decline (Nozaki et al. J Alzheimers Dis, 2021): Higher intake of fish, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA) in midlife significantly reduced risks of dementia.

3. 3. Intake of soy and the isoflavone and later cognitive decline (Svensson et al. J Alzheimers Dis, 2021): Compared to the lowest dietary quartile of energy-adjusted isoflavone genistein intake, the highest quartile was significantly associated with late-life cognitive impairment.

4. 4. Cancer/diabetes and later cognitive decline (Sadahiro et al. Psychiatry Clin Neurosci, 2019): Comorbid cancer and diabetes from midlife may increase the risk of MCI or dementia in later life. In addition to the increased dementia risk associated with diabetes on the basis of insulin resistance, cancer and cancer therapies may also interfere with cognitive function via insulin resistance.