The study of 35 obese or overweight adults compared the effects of vitamin C and exercise on the protein known as endothelin-1, which has a constricting action on small blood vessels.
The protein’s activity is raised in overweight and obese people and because of this high endothelin-1 activity, small vessels are more prone to constricting, becoming less responsive to blood flow demand and increasing the risk of vascular disease.
The study’s abstract is being presented at the American Physiological Society’s 14th International Conference on Endothelin, taking place in Savannah, GA.
The researchers explain that exercise has been shown to reduce endothelin-1 activity, but including it in a daily routine can be challenging. 
Daily dose as helpful as walking
Caitlin Dow, PhD, postdoctoral research fellow at the University of Colorado, Boulder, led the study to examine whether vitamin C supplements, which have been reported to improve vessel function, can also lower endothelin-1 activity.
The researchers found that daily supplementation of vitamin C at a time-release dose of 500 mg daily reduced endothelin-1-mediated vessel constriction as much as walking did.
The 35 sedentary, overweight/obese adults completed 3 months of either the supplementation (20 participants) or aerobic exercise training (15 participants).
Measures included forearm blood flow and responses to intra-arterial infusion of endothelin-1 before and after each intervention.
Vasoconstriction to endothelin-1 increased similarly – about two-fold – in response to both interventions.
Turning to the other end of the spectrum of physical fitness, a review in February 2013 found that vitamin C may help people under heavy physical stress, such as marathon runners, cut their chances of getting a cold.
In June 2013, it was reported that vitamin C consumption can cut the risk of people with asthma developing exercise-induced bronchoconstriction
