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.

Participants will be required to visit the lab twice. During each visit, beta-adrenergic receptors will be stimulated with isoproterenol. The two visits are identical in every way with one exception: during one visit the isoproterenol will be delivered with saline only, and during the other visit the isoproterenol will be delivered with saline and vitamin C. The order of the visits will be randomized. Body temperature will be measured with a thermometer and a thermal camera. venous blood will be sampled and circulating vitamin D concentration will be quantified.

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.)