The massive doses could reduce levels of stress hormones in the blood, they claimed.

High levels of stress disrupt the body's immune system, making it more vulnerable to a wide range of illnesses.

However, humans would have to consume thousands of milligrams of the vitamin to get such benefits, while the recommended daily allowance is only 60.

Dr Samuel Campbell and colleagues at the University of Alabama conducted the study and presented their findings at the annual meeting of the American Chemical Society in New Orleans.

Stressed rats

"Young, adult male rats were force-fed 100 mg of vitamin C by mouth twice daily at 12-hour intervals for a period of three weeks," they said.

"Stress was produced daily by one hour of complete physical restraint in a wire mesh cylinder cage.

"Randomly during the immobilization stress, the rats were placed in a heads-down position for 15 minutes."

The rats were then killed and examined.

The researchers found that the rats who had the vitamin C had far lower levels of stress hormones than those who did not.

Fewer symptoms

"The vitamin C treatment also reduced the other typical indicators of physical and emotional stress," they said.

These include weight loss, enlarged adrenaline glands and changes in parts of the immune system.

They suggest that while current recommendations on vitamin C are intended solely to prevent scurvy, greater health benefits may come from eating more.

Vitamin C - or ascorbic acid - is an essential vitamin that must be replaced everyday.