Effects of Cocoa Flavanols on Cognitive Function during Severe Oxygen Deprivation

Abstract

The brain has a high energy expenditure and is extremely sensitive to hypoxia; this can be a risk for groups acutely exposed to low oxygen situations through equipment failure (e.g., aircrew and technical divers) and where oxygen availability is compromised in neurological conditions (e.g., ischaemic stroke). Prophylactic dietary interventions may protect against hypoxia-induced cognitive impairments. In particular, flavanol-rich cocoa (FRC) shows promise due to its vasodilatory properties and beneficial effects on cerebral blood flow and cognition at sea level. This thesis investigated the effects of altered oxygen and carbon dioxide (O2 and CO2, respectively) availability and acute FRC ingestion on simple and complex task performance. A systematic review, meta-analysis and meta-regression (Chapter 2) demonstrated that acute hypoxia impairs multiple neurocognitive domains, and that response accuracy is impaired to a greater extent than response speed. A second meta-analysis showed that CO2 exerted a significant neuroprotective effect on simple task performance during hypoxia. This work was extended in Chapter 4, which showed that this neuroprotective effect also occurs during complex tasks under hypoxia. However, these improvements in cognition did not appear to be due to improvements in cerebral oxygenation. Chapter 5 demonstrated that benefits of an acute high dose of cocoa flavanols (~1000 mg) on cognition, cerebral oxygenation and subjective fatigue in normoxia persist in poikilocapnic (uncontrolled CO2) but not isocapnic (CO2 maintained at the normoxic level) hypoxia. This cocoa flavanol paradigm was extended in Chapter 6 by using a virtual reality flight simulator to assess realworld task performance in pilots. Participants ingested 1000 mg of cocoa flavanols 90 minutes before completing a flight performance task during normoxia and then hypoxia. Flavanols increased minute ventilation and the partial pressure of end-tidal CO2; however, flight performance was not impaired by hypoxia and was not affected by flavanols. This thesis demonstrates the potential neuroprotective effects of FRC on cognition during severe poikilocapnic hypoxia. These findings suggest that a simple acute dietary intervention with FRC may have potential as a prophylactic in applications where oxygen availability is compromised by environmental or neurological conditions.