A small study’s measures of blood-vessel tone suggest there are substantial benefits from modest aerobic exercise — or from just taking a moderate daily dose of vitamin C.

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Overweight and obese people who take a high-dose of supplementary vitamin C daily may get some of the cardiovascular benefits of exercise without the exercise, new research has found.

In a small trial that recruited sedentary adults who were overweight or obese, study participants who took 500 milligrams of vitamin C daily saw equal improvement in blood-vessel tone — a key measure of cardiovascular health — as did those who took up a three-month regimen of brisk walking five to seven times a week, investigators at the University of Colorado at Boulder reported.

The results were presented in Atlanta this week at the American Physiological Society’s annual meeting. But they have not been published in a peer-reviewed journal and so are considered preliminary.

The study’s small size — 15 subjects got the walking treatment, while 20 took the vitamin C supplements — may also limit the uptake of its findings by public-health officials, who have struggled, with limited success, to get sedentary Americans off the couch. Some 4 in 10 American adults are thought to be entirely sedentary.

But the study’s invasive measures of “endothelial function” — blood vessels’ ability to contract and dilate as needed — suggested that the benefits of modest aerobic exercise and of vitamin C were substantial.

At the start of the trial, all study subjects were sedentary and overweight or obese, and all showed levels of vascular tone that were impaired. In a pattern typical for overweight and obese adults who don’t get much exercise, their blood vessels did not respond to experimental conditions with the strength and suppleness seen in normal, healthy adults.

Their poor vascular tone sets off a cascade of harmful effects, including inflammation and changes in the blood that favor the formation of clots. As a result, these subjects were at increased risk of developing high blood pressure and having heart attacks and strokes.

The average ingoing body mass index (BMI) of exercisers was 29.3 and for the vitamin C group, 31.3 (a BMI between 25 and 29.9 is considered overweight, and obesity is diagnosed at a BMI of 30). During the study’s three-month duration, neither group lost weight.

Both three months of moderate-intensity exercise and three months of vitamin C supplements drove subjects’ vascular tone back into healthy territory. But the vitamin C did so without the burning of shoe leather or the exertion of walking.

The study’s lead author, Caitlin Dow, said the findings were particularly important for people who cannot exercise because of injury or physical limitations.

“This is not ‘the exercise pill,’ ” said Dow, a postdoctoral fellow at Colorado who conducts research on nutrition and vascular biology.

Dow emphasized that engaging in regular physical activity appears to have broader effects — lowering “bad” cholesterol, improving metabolic function and boosting mood and cognitive function — than does vitamin C.

For those able to get out and walk, or to hit the gym’s cardio equipment, that makes exercise a healthier option, she said.

But if a supplement that is widely taken and is safe for most people can mitigate some of the risks of excess weight, it may have broad benefits, she said. That’s especially important because only a very small minority — fewer than 1 percent, by a recent estimate — of those with established obesity succeed in losing and keeping off enough weight to return to al healthy weight.

“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.”

A moderate supplemental intake of vitamin C is between 30 and 180 mg a day, so 500 mg a day is a relatively high dose. But the tolerable upper limit for adults of vitamin C is 2,000 mg. Because it is a water-soluble vitamin, any vitamin C that is not used is excreted in urine. The most common complaints with high doses of vitamin C are diarrhea, nausea, abdominal cramps and other gastrointestinal disturbances.