Dose-related effects of inhaled essential oils on behavioural measures of anxiety and depression and biomarkers of oxidative stress

Ethnopharmacological relevance: Essential oils (EOs) are extracts of organic, volatile metabolites of plants that are typically oily liquids at ambient temperatures. Inhalation of EOs can regulate brain health and functions associated with mood and neurodegeneration, reflecting their bioavailability to brain. The aim was to identify physicochemical properties that influenced EO volatility and pathways of brain uptake by inhalation. Materials and methods: Dose-dependency of effects, determined as: total EO intake (μg/g bodyweight-BW), and rate of EO intake (μg/hr/g-BW), was determined by meta-analysis of data from animal studies (10 studies, 12 EOs), measuring effects on anxiety, depression and selected biomarkers of oxidative stress and inflammation (OSI). Results: Results demonstrated benefits on animal behavior at EO intakes of 1–100 μg/g BW and 1–10 μg/hr/g BW (Elevated Plus Maze and Forced Swimming tests) and <100 μg/g BW and 10–100 g/hr/g BW (Marble Burying). EOs regulated OSI biomarkers at intakes of 10–100 μg/g BW and 1–10 μg/h/g BW, and a dose-dependent elevation of dopamine at >1000 μg/g BW and 100–1000 μg/hr/g BW. Conclusion: The results support that EO ‘aromatherapy’ can promote dose-dependent regulation of anxiety, depression and OSI and that efficacy requires optimization of dose.