Vitamin C is one of the safest and most effective nutrients, experts say. Though it may not be the cure for the common cold, the benefits of vitamin C may include protection against immune system deficiencies, cardiovascular disease, prenatal health problems, eye disease, and even skin wrinkling. The tolerable upper intake level (or the maximum amount you can take in a day that likely won’t cause harm) is 2000 mg a day for adults. A recent study published in Seminars in Preventive and Alternative Medicine that looked at over 100 studies over 10 years revealed a growing list of possible benefits of vitamin C. "Vitamin C has received a great deal of attention, and with good reason. Higher blood levels of vitamin C may be the ideal nutrition marker for overall health," says study researcher Mark Moyad, MD, MPH, of the University of Michigan. "The more we study vitamin C, the better our understanding of how diverse it is in protecting our health, from cardiovascular, cancer, stroke, eye health [and] immunity to living longer." "But," Moyad notes, "the ideal dosage may be higher than the recommended dietary allowance." How Much Vitamin C Is Enough? Most of the studies Moyad and his colleagues examined used 500 daily milligrams of vitamin C to achieve health results. That's much higher than the RDA of 75-90 milligrams a day for adults. So unless you can eat plenty of fruits and vegetables, you may need to take a dietary supplement of vitamin C to gain all the benefits, Moyad says. He suggests taking 500 milligrams a day, in addition to eating five servings of fruits and vegetables. "It is just not practical for most people to consume the required servings of fruits and vegetables needed on a consistent basis, whereas taking a once-daily supplement is safe, effective, and easy to do," Moyad says. He also notes that only 10% to 20% of adults get the recommended nine servings of fruits and vegetables daily.