Methods In total, 1,628 Japanese community residents aged 60 and older without dementia were followed prospectively from when they underwent a screening examination in 2002–2003 to November 2012.

Results During the follow-up, 377 participants developed some type of dementia (247 AD, 102 vascular dementia). Higher serum elaidic acid levels were significantly associated with greater risk of developing all-cause dementia after adjustment for traditional risk factors. These associations remained significant after adjustment for dietary factors, including total energy intake and intakes of saturated and polyunsaturated fatty acids. No significant associations were found between serum elaidic acid levels and vascular dementia.

Conclusions The findings suggest that higher serum elaidic acid is a possible risk factor for the development of all-cause dementia and AD in later life. Public health policy to reduce industrially produced trans fatty acids may assist in the primary prevention of dementia.