1. Introduction
depression, cognitive decline, dementia, cognitive impairment
The effects of docosahexaenoic acid supplements on cognitive function have long been demonstrated, but the effects of alpha-linolenic acid, a precursor of docosahexaenoic acid, have not been fully tested. The search for functional foods that delay cognitive decline in the older adults is considered a very important area from a preventive perspective. The aim of this study was to conduct an exploratory evaluation of alpha-linolenic acid on various cognitive functions in healthy older subjects. Sixty healthy older adults aged 65 to 80 years, living in Miyagi prefecture, without cognitive impairment or depression, were included in the randomized, double-blinded, placebo-controlled clinical trial. Study subjects were randomly divided into two groups and received either 3.7 g/day of flaxseed oil containing 2.2 g of alpha-linolenic acid, or an isocaloric placebo (corn oil) containing 0.04 g of alpha-linolenic acid for 12 weeks. The primary endpoints were six cognitive functions closely related to everyday life: attention and concentration, executive function, perceptual reasoning, working memory, processing speed and memory function. After 12 weeks of intake, changes in verbal fluency scores on the frontal assessment battery at bedside, a neuropsychological test assessing executive function, in which participants are asked to answer as many words as possible in Japanese, were significantly greater in the intervention group (0.30 ± 0.53) than in the control group (0.03 ± 0.49, In Japan, a super-aged society, the number of patients with dementia is increasing, and it is estimated to exceed 7 million by 2025 [A growing body of research is showing that nutrients in foods have a positive impact on brain health maintenance suggesting an important role of nutrition in prevention. For example, the effects of diets containing docosahexaenoic acid (DHA), an ω-3 polyunsaturated fatty acid (PUFA) contained in fish oil, on cognitive function are becoming evident. According to a large meta-analysis, higher fish consumption is related to lower dementia risk [In addition to the direct inoculation of DHA, DHA precursors can be supplied as a means of promoting DHA synthesis in the body [Human studies have shown that consumption of perilla oil (equivalent to 4.3 g/day of ALA) for 12 months, assessed by the frontal assessment battery at bedside (FAB), showed changes in cognitive function after the test, compared to pre-intervention [Thus, although dietary ALA may affect cognitive function positively, we considered that there is little evidence for an objective ALA intervention effect and this needs to be more clarified. Therefore, we decided to conduct a randomized controlled trial to evaluate ALA in healthy older adults, in an exploratory manner, on various cognitive functions. Flaxseed oil containing high concentrations of ALA (60% of the fatty acid composition) was determined to be a suitable source of ALA. Assessment of cognitive function focused primarily on attention and concentration, executive function, perceptual reasoning, working memory, processing speed and memory function.