Menthol Stimulation of Brown Adipose Tissue in Humans: Aim 1

Inclusion criteria

• Fluency in English
• Participate in 150 minutes or more of at least moderate intensity exercise per week during the previous year. Assessment of moderate intensity physical activity will be determined via the International Physical Activity Questionnaire (i.e., IPAQ) (described in detail in Section 7.0). This questionnaire defines moderate intensity exercise as "activities that take moderate physical effort and make you breathe somewhat harder than normal".
• Body fat ≤ 30% as determined by DEXA scan
• Be cleared for physical activity according to the 2020 Physical Activity Readiness Questionnnaire (PAR-Q+).

Exclusion criteria

• Any autonomic cardiovascular, metabolic, neurologic, endocrine, or respiratory disease, that, in the opinion of the investigator, would exclude them from participation.
• Previously diagnosed liver and/or kidney dysfunction, including, but not limited to, acute and/or chronic kidney disease, cirrhosis, hepatitis, and fatty liver disease.
• Women who are pregnant or breastfeeding.
• Current use of tobacco or electronic cigarette, or regular (i.e., more than twice a week) use within the last 1 year.
• History of peripheral cold injury, skin disorder (eczema, psoriasis), or excessive tattooing.
• Known chronic (i.e., cancer, surgery) or acute conditions (i.e., diarrhea, constipation) of the rectum.
• Menthol allergy (described in detail in Section 7.0 and 9.0). Menthol can cause skin irritation when applied topically, especially for people with sensitive skin or allergies. For this reason, recruited participants will be screened for a menthol allergy during the informed consent/screening visit. We will apply a small quantity of the cream (\~2ml) to an isolated body area to limit skin exposure. In the case a rash develops during the application of the cream, research staff will irrigate the area to remove the substance and limit further exposure. A 24-hour follow-up phone call initiated by research staff will be implemented to follow-up on all adverse reactions. Detectable BAT activation during a localized cold stress test (i.e., face cooling test) (procedure described in detail in Section 7.0).
• Using medications with direct effects on the cardiovascular system including, but not limited to:
• Anticoagulants.
• Antiplatelet agents.
• ACE Inhibitors.
• Angiotensin II receptor blockers.
• Angiotensin-receptor neprilysin inhibitors.
• Beta blockers.
• Calcium, potassium, or sodium channel blockers.
• Cholesterol lowering medications.
• Digitalis preparations.
• Vasodilators.
• Anticholinergics.