It is well known that ω3 fatty acids are deeply involved in the cardiovascular system, lipid metabolism system, and maintenance of brain function. Omega-3 fatty acids, especially docosahexaenoic acid is abundant in the brain and plays an important role in maintaining brain functions. Although there are some negative opinions, the intake of ω3 fatty acids can be suppressed or delayed the progression of cognitive impairment, and further may help to prevent the onset of dementia not only for elderly people with age-related cognitive decline and mild cognitive impairment but also for patients with pre-clinical dementia by considering the time to start and the form of intake.

According to a WHO report, more than 20% of the world’s elderly population (aged 60 or above) suffers from psychiatric and neurological disorders, with the most common psychiatric and neurological disorders being dementia and depression, which affect approximately 5% and 7% of the world’s elderly population, respectively¹⁾. A major difference from depression in younger people is that in the elderly, depression is associated with heart disease, cerebrovascular disease, and dementia²⁾, which may delay diagnosis and treatment in primary care and maybe overlooked untreated. Therefore, primary prevention through lifestyle improvement is important. Nutritional approaches have been widely reported over the past 20 years, and among them, seafood and its active ingredient, ω3 polyunsaturated fatty acids (hereinafter referred to as ω3), are considered to be the most promising. Results of meta-analyses integrating observational studies have been associated with risk reduction^{3, 4)}, and meta-analyses of intervention studies have also shown a beneficial effect⁵⁾. In this review, we would like to discuss the relationship between seafood, ω3, and depression in elderly subjects and the mechanism of the association, including reports from our studies.

Westernization of the diet continues to reduce the chances of ingesting omega-3 fatty acids, and there are concerns about chronic shortage of omega-3 fatty acids. In an aging society, the increase in the number of people requiring long-term care, such as bedridden and difficulty walking, hinders the extension of healthy life expectancy. One of the possible causes is atrophy of skeletal muscles, especially fast muscle tissues, with daily lack of exercise and aging. In this time, we will introduce the results of two muscle atrophy models, focusing on the action of omega-3 fatty acids on muscle tissue. Omega-3 fatty acids were resistant to the weight loss of fast muscle tissues in both the hindlimb cast immobilization model and the hindlimb unloading model. In addition, in the hindlimb cast immobilization model, it was confirmed that ingestion of omega-3 fatty acids promoted muscle protein synthesis by exercise stimulation. This suggests that the intake of omega-3 fatty acids may suppress the atrophy of fast muscle tissues associated with aging and reduce the risk of difficulty in independent living for the elderly.