We all know we should be exercising more, and the reasons why have never been clearer. With obesity on the rise around the world, and a staggering two-thirds of Americans aged 25 years or older now being overweight or obese, it's important to make time to exercise and avoid the life-shortening consequences of not doing so.

Or is it? A new study suggests that at least some of the benefits of exercise can be achieved without even getting up off the couch. Researchers have found that by simply maintaining a daily dose of vitamin C (500 mg), a group of overweight and obese participants saw equal improvement in their blood vessel tone as those who undertook a three-month regimen of brisk walking several times per week.

But before you frantically rush out dawdle leisurely to the shops to buy up all the OJ you can carry, it's worth considering a couple of points.

Firstly, the measurement taken in the study (specifically, the tracking of blood vessel constriction due to elevated levels of the protein endothelin (ET)–1) is not the sole measure of cardiovascular health – it's just one part of the puzzle. There's also the extremely small sample size to bear in mind. Just 35 volunteers took part in the experiment, with 15 subjecting themselves to exercise and 20 taking vitamin C supplements.

"This is not 'the exercise pill'," study author Caitlin Dow from the University of Colorado, Boulder in the US told Melissa Healy at The Los Angeles Times. But nonetheless, the findings could have implications for those who are unable to exercise or find it difficult to do so.

While none of the participants in the three-month experiment lost weight, by taking vitamin C or performing moderate exercise, they all showed significant improvements in their vascular tone, with a demonstrated reduction in ET–1 activity.

"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, it's important to know what other lifestyle changes we can offer people who can't exercise."

The research was presented this week? at the 14th International Conference on Endothelin: Physiology, Pathophysiology and Therapeutics.