The acute and chronic effects of Lemon balm (Melissa Officinalis L.) extract on sleep quality, mood, cognition and endothelial function in healthy young to middle-aged adults

Lemon balm is a perennial herb that has been ascribed actions on sleep, cognition, mood and vascular health. My thesis aimed to determine these effects across three randomised controlled trials. Firstly, I determined the 4-week effects of daily lemon balm extract (LBE) on sleep quality and mood relative to a placebo in healthy adults with mild sleep complaints showing that both LBE and placebo had significant effects on sleep quality and mood. Bedtime cortisol also increased following LBE, suggesting that LBE boosted lower cortisol levels in adults with mild sleep problems. Secondly, the acute effects of a dose of LBE on cognition and mood during periods of cognitive overload were investigated in healthy adults with moderate stress complaints. LBE intervention showed cognitive benefits at 5 h following supplementation in the hardest executive trials, where accuracy performance was associated with feeling calmer and more content. Furthermore, a maintenance of diastolic blood pressure was seen for LBE during cognitive overload. Finally, the effects of LBE on vascular health in healthy adults was assessed where LBE showed increases in shear rate at 1.5 h following intake, and with no changes in endothelial function, indicating an increase in blood flow velocity. This programme of research is the first to demonstrate that LBE had acute effects on cognitive performance associated with changes in transient mood, calmness and contentedness. The greatest effect on cognitive performance was seen at 5 h, and at 1.5 h for blood flow velocity. It is still unclear if the increase in bedtime cortisol is associated with sleep quality following 4-weeks of LBE intake, as the placebo group also improved in sleep quality. Future work should assess the effects of LBE on cortisol changes associated with sleep-wake patterns in those with sleep problems and assess the action of LBE in stressed adults with effects associated with executive function, mood and blood flow velocity up to 5 h following intake.