Considering the amount of vitamin C in common foods, this level is nearly impossible to reach without supplementation. For example, an apple has about 8.5 mg of vitamin C, an avocado has about 20 mg and a cup of blackberries has about 30 mg. So unless you’re eating 250 apples a day you probably don’t have to worry.

Where we run into the potential for an overdose is with supplementation. The popular supplement Emergen-C contains 1000 mg per serving and other competing products contain similarly high amounts. It’s very easy to exceed the UL of 2,000 mg a day through supplementation.

Despite the upper limit of 2,000 mg, however, symptoms generally don’t occur at intake levels below 4,000 mg a day, and even then, it’s generally just mild nausea and diarrhea.

Intravenous doses of vitamin C have been shown to be safe up to 120 g/day, or 120,000 mg. 

Should I Supplement Vitamin C?

Although I rarely advise supplementing vitamins that can be obtained from diet alone, there is substantial evidence that vitamin C deficiency is widespread and that supplementation may lead to various health benefits.

Vitamin C deficiency can result in health problems ranging from joint pain to bleeding gums to hair loss and muscle loss. Severe deficiency can result in death. Moreover, research suggests that vitamin C supplementation may reduce risk of heart disease and increase lifespan.

The NHANES study found that men supplementing 800 mg of vitamin C per day lived on average 6 years longer than those getting the Recommended Daily Allowance (RDA). Additionally, the multi-million dollar Nurses Health Study found that vitamin C supplementation was associated with a 28% lower risk of heart disease.

Given the dangers of deficiency and the substantial potential for benefits from supplementation, it makes sense to supplement vitamin C, especially because the symptoms of overdose are relatively mild.

A safe, but effective estimate for supplementation is 500 to 1000 mg per day, and slightly more for the sick and the elderly.

A Note on Vitamin C and Cancer

Vitamin C in the body protects all human cells against injury, including cancer cells. For this reason, vitamin C supplementation reduces the effectiveness of  chemotherapy. Those with cancer should obtain vitamin C intermittently and avoid supplementation while undergoing chemotherapy.

Most other diseases seem to be helped by vitamin C supplementation, or not affected.

Other Important Supplements

Like vitamin C, most other vitamins and minerals can hypothetically be obtained from diet alone, but research suggests that there are substantial benefits to supplementing certain vitamins. This post looks at optimal levels of vitamin D intake and emphasizes the importance of picking the right kind of vitamin D supplement. Another post on vitamin B12 will be particular important for vegetarians and vegans. Various other articles on health and supplementation can be found in the sidebar.