WASHINGTON - Vitamin C may be able to prevent diseases ranging from colds to cancer by reducing the effects of stress on the body, researchers said Sunday. They said tests on rats suggested that megadoses of vitamin C could reduce the levels of stress hormones in the blood - hormones which can damp down the immune system by triggering an increase in fats and crippling the body's ability to clear out LDL cholesterol. Samuel Campbell and colleagues at the University of Alabama said their findings suggest that early humans probably ate a lot more fruit than modern humans do - fruit that is high in vitamin C. Human beings may have a high intrinsic need for vitamin C, the scientists said, noting that current recommended daily allowances for vitamin C are designed merely to prevent scurvy. Optimal health benefits might come from eating more vitamin C, they said. In their experiment, the scientists stressed laboratory rats and gave huge doses of vitamin C to some. "Young, adult male rats were force-fed 100mg of vitamin C by mouth twice daily at 12-hour intervals for a period of three weeks," the researchers said in a statement. Reporting to the annual meeting of the American Chemical Society in New Orleans, they said this was the equivalent of a human eating several thousand milligrams of the vitamin. "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," they added. Then they killed the rats and looked at their adrenal glands, which produce stress hormones, and other organs. The vitamin C significantly reduced the levels of stress hormones in the rats' blood, they found. "The vitamin C treatment also reduced the other typical indicators of physical and emotional stress," they added - indicators which includes losing weight, enlarged adrenal glands and changes in the thymus and spleen, which help produce immune cells. Studies aimed at showing whether vitamin C supplements can prevent colds or shorten their duration have had mixed results.