Metabolic Health and Cognitive Function : The Roles of Lifestyle and Shift Work

Sammanfattning: The risk of cognitive impairment and metabolic disturbances increases during aging. Healthy lifestyle habits, such as a regular intake of fatty fish and adherence to the Mediterranean diet (MeDi), have been shown to slow age-related cognitive decline and decrease the risk of metabolic disturbances. Conversely, poor lifestyle habits including habitual short sleep duration as well as irregular work schedules (e.g. night shift work) have been correlated with lower cognitive performance and increased risk of having metabolic syndrome (MetS). However evidence is not conclusive regarding the above mentioned associations. The aim of this thesis was to investigate associations of diet, sleep, and shift work with metabolic health or cognitive performance in two Swedish cohorts.In Paper I and II we examined whether the dietary intake of omega-3 fatty acids and adherence to MeDi were related to measures of brain health in elderly subjects. To this aim, we used scores from the 7-minute cognitive screening test (7MS) and brain volume determined by magnetic resonance imaging. In Paper I, self-reported dietary intake of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) at age 70 was positively associated with cognitive performance and global gray matter volume at age 75. In Paper II, the fully-adjusted main analysis revealed that the MeDi score was not linked to measures of brain health. However, low intake of the MeDi component meat and meat products was associated with better performance on the 7MS and larger total brain volume.Paper III and IV included subjects aged 45-75 years. In Paper III we demonstrated that current and recent former shift workers (including shifts outside traditional working hours during the past 5 years at the time of the survey) performed worse on the trail making test (TMT) than non-shift workers. The TMT is a test evaluating executive cognitive function, and the performance on this test decreases with age. In Paper IV, sleep duration, sleep disturbances, and sleep-disordered breathing were all linked to an increased prevalence of MetS. Some of the observed associations were age-specific. For example, whereas both short and long sleep durations were linked to a higher prevalence of MetS in younger individuals (<65 years), only long sleep duration did so in the older participants. Collectively, the findings of this thesis suggest that maintaining healthy dietary habits, having high-quality sleep, and following a regular work schedule may be recommended strategies to mitigate age-related morbidities.