The absorption and metabolism of a single L-menthol oral versus skin administration: Effects on thermogenesis and metabolic rate.
OBJECTIVE To compare the effects of commercially sold menthol (3.5%) ointment and cold application on blood flow in the forearm. DESIGN : Prospective counterbalanced design. SETTING University research laboratory. PARTICIPANTS Twelve (6 men and 6 women) college-aged students. INTERVENTIONS Each participant had blood flow measured in the brachial artery for 5 minutes before and 10 minutes after menthol ointment or cold application to the forearm. MAIN OUTCOME MEASURES Blood velocity, arterial diameter size, and blood pressure were recorded during testing procedures. Vascular conductance was calculated based on these measures and used to describe limb blood flow. RESULTS We observed a significant reduction (35%; P = 0.004) in vascular conductance within 60 seconds of menthol and cold application to the forearm. Vascular conductance remained significantly reduced for 10 minutes by approximately 19% after both menthol and cold application [F(2.313, 43.594) = 10.328, P < 0.0001]. There was no significant difference between conditions [F(1, 19) = 0.000, P = 0.945]. CONCLUSIONS The application of a 3.5% menthol ointment significantly reduces conductance in the brachial artery within 60 seconds of application, and this effect is maintained for at least 10 minutes after application. The overall decline in conductance is similar between menthol ointment and cold application.