Evaluation of the effect of aroma oil as a bath salt on cognitive function

Aromatherapy is a non-pharmacological therapy for the improvement of dementia symptoms. This study aimed to assess the effects of aroma oil as a bath salt on cognitive function, olfactory function and sleep quality.

This was a randomised controlled trial. Overall, 49 patients were able to provide consent, and 35 were finally analysed (Alzheimer's disease: 10, mild cognitive impairment: 25). The patients were randomly assigned to use 0.1%, 0.5% or 1% aroma bath salt. During daily bathing, bath salt was added to the bath water, and the subjects remained in the bathroom for ≥10 min. The intervention period was 24 weeks, and the observation periods were 4 weeks before and after using the aroma bath salt. We performed the Touch Panel-type Dementia Assessment Scale (TDAS), the Odour Stick Identification Test for Japanese (OSIT-J) and the Japanese version of the Pittsburgh Sleep Quality Index (PSQI-J) five times during the before and after observation periods and after the 12-week intervention.

There were no significant changes in the TDAS, OSIT-J and PSQI-J scores before and after the intervention in all groups. Moreover, there were no significant differences in the TDAS, OSIT-J and PSQI-J scores between the groups before and after the intervention. In the correlation analysis of changes in the TDAS and other tests during the intervention period, significant associations between TDAS and sleep latency and sleep disturbances, which are sub-items of PSQI-J, were observed in the use of 0.1% aroma bath salt group.

The use of aroma bath salt was not associated with improvement in cognitive function, olfactory function or sleep quality. However, sleep-related aspects were associated with changes in cognitive function before and after use of aroma bath salt, which suggested that there is a link between improvements in sleep and that in cognitive function.