Does Vitamin C Increase the Body Heat Generated By The Nervous System?

The goals of this clinical trial are to determine whether or not vitamin C is able to: (1) increase the body heat generated by the sympathetic nervous system; and, (2) increase circulating vitamin D concentration during sympathetic nervous system stimulation in adult humans aged 18-40 years who meet the criteria for overweight based on body mass index. The main question it aims to answer are: 1. By how much does body temperature increase during stimulation of beta-adrenergic receptors when vitamin C is given. 2. By how much does circulating vitamin D concentration increase during stimulation of beta-adrenergic receptors when vitamin C is given. Participants will will be asked to: * undergo measures of body temperature * have blood sampled on two separate occasions: once during stimulation of beta adrenergic receptors, and once during stimulation of beta-adrenergic receptors while also been given vitamin C.

Inclusion Criteria: * Age 18-40 years (inclusive) * Body mass index greater than or equal to 25 kg/m2 and less than 30 kg/m2 * Weight stable (no change in body mass greater than 5 Lbs. within the previous 6 months. * Willing to abstain from caffeine and alcohol for 24-hours prior to two different study visits * Competency in English as assessed by comprehension of the Informed Consent. This is study involves invasive procedures and infusion of a systemic vasoactive agent (isoproterenol); for safety reasons, the ability for clear and rapid communication will be necessary between the research participants and the investigators. Exclusion Criteria: * History of autonomic, cardio-pulmonary, and/or metabolic disease (including heart failure, hypertension, arrhythmia, vascular disease, and/or diabetes) * Pregnancy or breast feeding * Habitual use of tobacco/nicotine products or recreational drugs (2 or more uses within the previous month) * History of a "sulfite allergy" as it is a relative contraindication to isoproteronol use. * Has ingested vitamin supplements and/or antioxidant supplements during the previous 4-weeks (e.g. Vitamin C, Vitamin E, Multi-vitamins, etc.)