Since it’s not a food or used as edible coloring, we don’t have it in our database of ORAC values (antioxidant levels). But if we did, the ORAC value of pure vitamin C powder (ascorbic acid) is a staggering 1,019,690.

To put that into perspective, it’s 218 times higher than fresh blueberries when comparing equal weights.

That million unit value is according to testing done at the University of Oslo. Not with some proprietary or patented formulation like Ester-C, but just plain ol’ generic CVS vitamin C 500 mg tablets. Kirkland Signature (Costco) tested comparably. 100g samples of each were used for measuring. (1)

It still can’t compete with the antioxidant power of astaxanthin, but among the readily available and cheap supplements, nothing outranks the C.

Granted, the amount of research on it is dismal in comparison, but with astaxanthin, even relatively high dosages have demonstrated safety in animal and human studies. That’s surprising, being that it is a fat soluble substance. The same can’t be said about large doses of C, even though it’s water soluble. (2) (3)

Is it possible to overdose on vitamin C?

Yes. Vitamin C is a water-soluble vitamin, which makes larger amounts much safer than fat-soluble vitamins, like A and E. Still, there are side effects of vitamin C to be aware of and their likelihood correlates with dosing. Diarrhea, nausea, bloating, and cramps are mild symptoms of megadosing, while severe effects can include kidney stones and being pro-oxidant.

Supplement companies will often embellish the health advantages, while doing a poor job pointing out the disadvantages.

Side effects of vitamin C

  • Abdominal cramping
  • Gas and bloating
  • Diuretic effect
  • Headache
  • Kidney disease
  • Increases iron absorption which is dangerous for hemochromatosis disorder
  • May affect blood sugar levels in diabetics
  • Risk for those with corn allergy
  • Possible drug interactions with chemotherapy medications, nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, acetaminophen (Tylenol), warfarin, tetracycline, protease inhibitors, birth control pills, and antacids containing aluminum

The good news is that with many of these adverse reactions, research suggests they are rare since the warnings are based on isolated case reports and studies. The more common side effects – like diarrhea and digestive discomforts – are typically only associated with large amounts being used (2,000 mg or more of ascorbic acid per day).

The biggest danger comes with the possibility of prescription medication interactions. If a drug isn’t working properly, there could be serious or potentially lethal consequences. This is why you should consult your doctor prior to taking vitamin C tablets if you are on any medication. Overdosing could occur with even low amounts. (4)

Can you be allergic to vitamin C?

Technically, no. The isolated vitamin of ascorbic acid is an essential nutrient for human health and you would die without it. However you can have an allergic reaction to vitamin C tablets, face cream, serum, and drinks containing it. Since ascorbic acid is often made using corn, those with an allergy to that plant are at risk.

Allergy to vitamin C causes are unlikely to be from corn since that is a very rare allergy. Plus, the potential amount of allergens remaining – residual protein matter from the plant – would likely be in a concentration of only parts per million (ppm). If you are experiencing ascorbic acid intolerance it’s likely you are allergic to another ingredient in that supplement, fortified food, or skin cream.

On a related note, there’s a strong likelihood the corn used is genetically modified. If you want non-GMO ascorbic acid, then make sure the packaging is labeled as such. Organic food-derived sources will always be non-GMO.

Almost all ascorbic acid is made in China

Chinese flag in dark and snowy weatherTo be clear, we are not inferring or implying that products using vitamin C made in China are less safe. With proper manufacturing processes and quality control, the molecule of ascorbic acid will be identical regardless of where it was made.

Still though, many consumers – ourselves included – simply prefer to buy foods and supplements made in America, UK, and other countries which have a better reputation for both quality control and human rights.

How much is made in China? The New York Times reports 80% and that was years ago.

That percentage is likely even higher today. (5)

Now here’s the real disgusting part. A dirty secret in the supplement world is that when a product says made in the USA, that doesn’t mean the active ingredient are from America.

A company can legally claim to be US-made if the actual product – capsule, tablet, etc. – is manufactured in this country. As far as where the active ingredients come from, that can be anywhere in the world and there’s no legal requirement to disclose it to you.

In fact, many supplement brands refuse to cite the country of origin, claiming it’s a trade secret. Yeah right, one can guess what their real motive is for not telling you… they don’t want to tell you it’s coming from China!

Megadoses may lead to kidney stones

According to the National Institutes of Health Office of Dietary Supplements, the highest recommended dietary allowance (RDA) for vitamin C is 120 mg per day. That’s only for 19+ year old women who are breastfeeding. Smokers are also advised to use an extra 35 mg per day.

For non-smokers and those who are not pregnant, the RDA is 90 mg for men and 75 mg for women.

All of those amounts are said to be “much higher” than the minimum required to protect against vitamin C deficiency. (6)

Being water soluble, you can use more safely and there is plenty of science to suggest benefits of doing so. How much vitamin C should I take per day?

The following are the Tolerable Upper Intake Levels (ULs) according to the same U.S. government source.

Tolerable Upper Intake Levels (ULs) for Vitamin C
Age Male Female Pregnancy Lactation
0–12 months Not possible to establish* Not possible to establish*
1–3 years 400 mg 400 mg
4–8 years 650 mg 650 mg
9–13 years 1,200 mg 1,200 mg
14–18 years 1,800 mg 1,800 mg 1,800 mg 1,800 mg
19+ years 2,000 mg 2,000 mg 2,000 mg 2,000 mg
*Formula and food should be the only sources of vitamin C for infants.

In adult men and women, 2,000 mg per day of ascorbic acid is considered to be the maximum safe amount to use on a long-term basis. This limit is for the total combined intake coming from both food and supplement sources. Exceeding this dose will increase the risk of side effects.

What is megadosing? There is no official definition but generally it’s when nutrients are eaten or consumed in amounts far greater than the Tolerable Upper Intake Levels.

Is 2000mg of Vitamin C safe? For healthy adults, that daily dosage is the ceiling of the upper intake level and therefore, is believed to be safe according to the U.S. government. But what happens when you exceed that and start taking 3,000 mg, 5,000 mg, or even 10,000 mg per day as some megadosers do?

Let’s begin with what might be happening with even lower amounts.

Fat-soluble vitamins (A, D, E, and K) and other fat-soluble nutrients are stored in the liver. These can reach dangerously high accumulations if high amounts are used for extended periods of time.

With water soluble – like C and B vitamins – we excrete in our urine what we don’t use. You can’t overdose on C in the same way you can with a fat-soluble vitamin, like A. Because in 24 to 48 hours, your body will have rid itself of any excess.

diagram of human kidneysThe side effect of taking too many tablets or drinking multiple effervescent vitamin C powder drinks daily is that your kidneys have to work harder. Those are the two bean-shaped organs which make your urine and they will be responsible for getting rid of any excess intake.

There are a number of studies which suggest too much vitamin C is bad for you, especially if you are more prone to developing kidney stones.

As published in the prestigious JAMA Internal Medicine journal, more than 22,000 Swedish men were evaluated over a 10+ year period. It was concluded that those taking 7 or more vitamin C supplements per week had double the risk of developing kidney stones. (7)

Of course the next logical question is, how many milligrams of the vitamin were they taking per day?

The researchers couldn’t definitively answer that, nor did they identify any brands taken. However they did point out that most supplements sold in Sweden have 1,000 mg per tablet. (8)

If using 7 or more average-dose tablets per week was associated with a doubling of risk, it would suggest that taking 1,000 mg or more per day over a long term period may be too much of this vitamin.

Taking 1,000 mg every day is an amount that’s well below the Tolerable Upper Intake, yet this study suggests it still may double the risk of getting kidney stones.

That’s the bad, but what about the good that may come from using a lot?

Nearly 20 years ago was study involving 715 young adults – students 18 to 32 years old – split between a control group and an experimental group. The latter of which used 1,000 mg of vitamin C per hour (not day, hourly) during the first 6 hours of having cold and flu symptoms. After that, they were taking it 3x daily (3,000 mg per day).

The results? The reported cold and flu symptoms in the vitamin C megadose group decreased 85% versus the control group, who were using pain relievers and decongestants. (9)

That was a short term study. It occurred over a year and the megadosing only happened when the participants thought they were getting sick.

There seems to be evidence to suggest high amounts in the short term may be beneficial. However the same over the long term is associated with danger to your kidneys. Particularly if you are a guy, since men are at increased risk for kidney stones.

Vitamin C can act as a pro-oxidant

What is a pro-oxidant? It’s the opposite of an antioxidant. Instead of neutralizing reactive oxygen species (ROS) it creates them by generating oxidative stress. This is a drawback that antioxidants can have to varying degrees, dependent on their concentration and the environment they are in.

In short, a pro-oxidant effect is the opposite of what you want!

diagram of Fenton and Haber-Weiss reactions

Fully describing the Fenton and Haber-Weiss reactions will have to be a topic for another time!

In the case of vitamin C, the concerning reason it can act as a pro-oxidant is because it has been found to reduce metal ions through what’s called the Fenton reaction. A symptom of overdose that you can’t even detect!

Describing the Fenton reaction in full will make your eyes glaze. The important thing to know about is that it’s considered one of the most powerful methods of oxidation. This effect has been theorized to be a contributor to Parkinson’s, Huntington’s, and Alzheimer’s diseases, among others. (10)

It’s inconclusive whether the thousands of different polyphenol antioxidants, which are non-vitamin micronutrients found in plants, also have the tendency to spur the Fenton reaction. Not to say they don’t, but at least to date, there’s not evidence to support that and research strongly suggests their antioxidant activity to be quite beneficial for your health. (11) (12)

On the other hand with ascorbic acid, there is a fair amount of research showing it can have a strong pro-oxidant effect in certain conditions. This is through that Fenton reaction and it’s not just based on lab research (in vitro). Vitamin C exhibits prooxidant properties in vivo, meaning it’s been demonstrated in living organisms. (13)

What makes ascorbic acid unique is that it can recycle ferrous iron ions to continue to generate ROS, with more Fenton cycles. This is why vitamin C and iron (without an iron chelator) is a bad combo.

Now when all antioxidants react with dissolved oxygen they generate hydrogen peroxide as a byproduct, which in itself is a ROS (pro-oxidant). That may sound bad but isn’t always.

Dr. Linus Pauling is the only person in history to win two unshared Nobel Prizes, meaning he was deemed the sole person responsible. (14)

Late in his career he became be known as “the vitamin C man” because he reportedly used a 12,000 mg per day megadose and advocated for humans to use up to 6,000 mg, based on research from other primates. His theories on this were highly controversial and are still considered such by mainstream medicine, since benefits of megadosing have yet to be proven.

What’s intriguing though is that during the two decades since his death, research has found that the oxidative promoting effects of vitamin C might have cancer benefits. Although unproven, it has been proposed that since the shape of this vitamin is similar to glucose, cancer cells may uptake the C and metabolize it because they think it’s sugar (glucose).

chemical structures and molecular formulas for vitamin C and glucose

Cancer needs sugar and it’s why some chemotherapy drugs are combined with it – to promote their uptake.

Cancer cells generally have low amounts of catalase, which is an internally created antioxidant. Therefore, it is theorized that they have less natural defense against the hydrogen peroxide which is generated by the vitamin C coming in contact with dissolved oxygen. In turn, an increase in cell death might result if there is cellular uptake of the C and it’s creating hydrogen peroxide after getting inside. (15) (16) (17)

Now it is true that derivatives created by ascorbic acid have been found to induce cell death in cultured human glioblastoma (brain cancer) and renal carcinoma (kidney cancer) cell lines. Interesting, but keep in mind that’s lab research only. Just because something works in a Petri dish, it doesn’t mean the same thing will happen in the body. (18)

To reiterate, all of the cancer theories out there are unproven. It’s also worth mentioning that Dr. Linus Pauling – who reportedly was a megadoser – died himself of prostate cancer at the age of 93. Even if there is some benefit for cancer, it clearly wasn’t enough to help him!

As if two Nobel prizes weren’t enough of an achievement, six years before Dr. Pauling’s death he also wrote the New York Times bestseller How To Live Longer and Feel Better. In the book he explains his theories on allergies, arthritis, colds, cancer, and numerous other ailments and what role he believes nutrition might play in them.

Is vitamin C bad for you?

The most concerning pro-oxidant effect happens in the presence of free transition metals. Now these metals are something all of us have in our bodies, so it’s impossible to avoid 100%. Ascorbic acid is one of the most researched nutrients and to date, the overwhelming consensus is that it’s good for you even when this is factored in. (19)

Plus unlike dogs and cats, human are unique mammals in that we don’t internally create this vitamin. We literally don’t have a choice – we need to get it from dietary sources.

What we do have a choice on though is how much we consume. We know how much is needed to avoid scurvy and deficiency symptoms (which the RDA covers) and it’s the amount beyond that where the question mark remains… is more necessarily better?

A recent scientific review of its antioxidant and pro-oxidant activity in oral health sums up the current mindset quite well:

“The data validates the role of Vitamin C as an antioxidant under physiologic conditions exhibiting a cross over role as a pro-oxidant in pathological conditions. Further studies are required to substantiate its pro-oxidant activity to draw concrete conclusions.”

While that review was specific to oral health, the scientists factored in generalized pro-oxidant vs. antioxidant research, too. (20)

The verdict?

Any guru that alleges to know the right amount of vitamin C to take isn’t being honest.

The truth is that no one can definitively say. We know there are minimums required for human health and those small amounts are indisputable. When it comes to taking exponentially higher megadoses of 3,000 or 6,000 mg of vitamin C per day, there just isn’t enough science to conclude (1) if there are health benefits of doing so, (2) if those large amounts in the human body generate high amounts of ROS through the Fenton reaction, and (3) if any increase in ROS is outweighed by other benefits.

Daily intake of vitamin C equal to 1000 mg per day seems beneficial overall, at least based on the research to date. You could even make the case that 2,000 mg per day (which is the Tolerable Upper Intake Level) also might be better for you than just a couple hundred mg.

For amounts above the Upper Intake Level (2,000 mg) there are far fewer studies. Even at 1,000 or 2,000 mg, there’s still cause for concern relating to kidney stones when used long term. For some, even these moderate amounts may constitute a vitamin C overdose.

As you see, there are a lot of unknowns here.

What do we use ourselves?

We believe there is a reasonable burden of scientific evidence to suggest that on a short-term basis, taking large amounts of vitamin C might offer benefits which outweigh the potential risk of increased ROS generation. Based on studies, that may range from 1,000 mg to 5,000 mg daily for a period of days or weeks. However it’s important to remember that using beyond the RDA has not been proven to offer any increased health benefit. It should not be used for the treatment of any disease. High amounts should be viewed as a dietary supplement only.

For long term usage, such as several consecutive months or 1+ years, taking too much vitamin C does not seem worth it when you weigh the risk for kidney stone formation and the still lingering unknown of how much excess ROS might be created from its Fenton reactions.

During pregnancy, to avoid any potential risk for vitamin C toxicity or adverse reactions, we would stay within the Tolerable Upper Intake Levels both on a short and long term basis. That’s 1,800 mg per day for women 14 to 18 years of age who are pregnant or breastfeeding and for ages 19+ that’s 2,000 mg. (6)

All of us at Superfoodly use numerous supplements but we do not take vitamin C capsules or tablets on a daily or even weekly basis. Rather, we rely on a plant-based whole food diet that is already a rich source, combined with an organic multivitamin that provides a more moderate among for long term usage; 80 mg which equals 130% of daily value.

Best of all, that supplement is not ascorbic acid made in China. It’s coming from fruits and herbs used to formulate the multivitamin.

That brand we use is from Garden of Life. You can get their multivitamin for men and for women on Amazon.

For short-term bursts of higher dosed vitamin C supplements, ascorbic acid not made in China is only our second choice. Our first is fruit and vegetable derived vitamin C.

Garden of Life Vitamin Code raw vitamin C capsules

Garden of Life’s Vitamin Code raw vitamin C is an excellent option.

Another brand we like is Nutrigold, which does not use synthetic ascorbic acid.

Ultimately though, since each of us have unique physiology and needs, what we choose for ourselves should not be misconstrued as advice. You should consult your doctor before embarking on a new vitamin or supplement regimen, especially given the possibility of drug interactions.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.