It might be an essential nutrient, but vitamin C is water soluble — meaning your body doesn't make or store it and you flush out the excess daily, via pee. This means you need to eat vitamin C daily, which is really easy since the daily recommended intake is low, only 75 mg for women and 85 mg for men. You can easily achieve this by eating a cup of broccoli or an orange. But can you consume too much?
The upper limit of safety is considered to be 2000 mg a day, or two packets of Emergen-C, which we see our coworkers downing daily to fight off colds. Since the studies have shown that the body can really only absorb up to 200 mg a day, those packets might just be going down the toilet.
When the body cannot completely flush mega doses of vitamin C, you might experience diarrhea, nausea, vomiting, abdominal bloating, and heartburn. High doses taken on a regular basis may also put you at risk for kidney stones. Ouch.
Vitamin C's ability to prevent the common cold has been studied A LOT. Unfortunately for all us citrus-lovers, there is no evidence to support that taking it regularly can prevent the common cold, but it might just bolster the immune system. Vitamin C may shorten the duration of a cold, but timing is everything: you need to dose yourself at the onset of symptoms. It's best to spread your intake throughout the day. As for dosing? Dr. Weil, MD, suggests not topping 1000 mg daily, and Dr. Axe, a chiropractor and doctor of natural medicine, suggests topping out at 4000 mg daily for the duration of your cold. After your symptoms clear, all the extra C is useless, since you will just be peeing it out.