Vitamin C may mimic some of the effects of exercise in overweight and obese individuals. 
The protein endothelin-1 (ET-1) has a constricting action on small blood vessels. This activity is increased in overweight and obese individuals, making small blood vessels more prone to constrict and less able to handle blood flow demand, increasing the risk of vascular disease. At the start of the study, all of the participants had impaired vascular tone.
Caitlin Dow, PhD, postdoctoral research fellow at the University of Colorado, Boulder, and colleagues followed 35 sedentary, overweight or obese adults throughout three months. Twenty participants took supplements during that time but did not increase their activity, while 15 subjects took a brisk walk 5 to 7 times a week.
No one in either group had lost any weight at the end of the study, but the scientists found that taking 500 mg of vitamin C supplements daily reduced ET-1 related blood vessel constriction as much as walking did. Exercise and vitamin C intake together was found to return the participants’ vascular tone to normal…but participants who took vitamin C alone also experienced the same health benefits.
Poor vascular tone can lead to a downward health spiral, starting with inflammation and changes in the blood that can cause stroke. All of the study’s participants were found to be at increased risk of developing high blood pressure and suffering heart attacks and strokes.
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The results of the study, presented in Atlanta last week at the American Physiological Society’s annual meeting, represent good news for people who cannot physically exercise. But for everyone else, warns Dow, the study’s author, it’s still important to get off the couch and start moving. 
“This is not ‘the exercise pill,’” she said.
In addition to improving vascular tone, regular exercise also helps lower “bad” cholesterol, improves metabolic function, and boosts mood and cognitive function.
Yet, like regular exercise, taking vitamin C – a supplement generally recognized as safe – may also have broader implications. It may be able to cut some of the risks linked to obesity, and since those with established obesity rarely succeed at losing weight and keeping it off (fewer than 1%), every little bit helps.
“If we can improve different measures of risk for disease without changing weight, it takes a little bit of the pressure off some people,” Dow said. While Vitamin C “certainly isn’t a new cure,” she added, “it’s important to know what other lifestyle changes we can offer people who can’t exercise.”
Jessica Jones-Smith, an expert on human nutrition at Johns Hopkins University’s School of Public Health, warns, however, that vitamin C may not be the “quick fix” the results might make it out to be.
“At the same time, we should be cautious in interpreting these findings,” said Jones-Smith. In addition to the preliminary nature of the results, “it is not clear that improved vascular tone” — the principal outcome measured in the trial — “will translate to decreased risk of cardiovascular disease.”
A dose of 500 mg of vitamin C a day is fairly high – a moderate dose is considered between 30 and 180 mg per day. Technically, the body can tolerate up to 2,000 mg a day, but such a dose may be accompanied by gastrointestinal disturbances.