Dietary inflammation, sleep and mental health in the United Kingdom and Japan: A comparative cross-sectional study.

Diet has been repeatedly shown to affect mental and sleep health outcomes. However, it is well known that there are cross-cultural differences in dietary practices as well as the prevalence of mental and sleep health outcomes. Given that the dietary inflammatory potential of diets has been linked to mental and sleep health outcomes, in the current study we sought to assess the inflammatory status of habitual diets and examine its relationship with mental and sleep health outcomes in both the United Kingdom and Japan. Our aim was to determine if the associations between the dietary inflammation index (DII) score and these health outcomes could elucidate any potential cross-cultural differences in health. Online survey data was collected from 602 participants (aged 18-40 years) in the United Kingdom (n = 288) and Japan (n = 314). Participants self-reported their dietary intakes, as well as current mental health and sleep patterns. The DII score was calculated (score range - 2.79 to 3.49) We found that although participants in the United Kingdom reported better overall mental wellbeing, participants in Japan reported less severe depression, anxiety and stress and better subjective sleep quality, less sleep disturbances and daytime dysfunction, despite sleeping shorter, and a better adherence to an anti-inflammatory diet. Moreover, across the United Kingdom and Japan, adherence to more anti-inflammatory diets predicted higher levels of subjective sleep quality, fewer sleep disturbances, less use of sleep medicine and less daytime dysfunction. In conclusion, there are several differences between mental and sleep health outcomes in the United Kingdom and Japan, which could be attributable to the inflammatory potential of respective regional diets. Future studies are warranted to examine the mental and sleep health benefits of adhering to anti-inflammatory traditional Japanese diets in clinical and subclinical cohorts.