PSA: Vitamin C Supplements Can Cause These Surprising Side Effects

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Whether taken orally for its immune health benefits or applied via a serum to promote glowing skin, vitamin C seems to always be trending—and for good reason!* 

Vitamin C plays key roles in immune, cognitive, cardiovascular, and skin health, as well as iron absorption and collagen synthesis.* But since the body can’t produce it spontaneously, we have to seek C out in food sources, and many people do a less-than-stellar job at meeting their daily needs: Almost half of American adults have a vitamin C gap in their diet, and an estimated 108 million of us have insufficient vitamin C levels, per blood tests. (That’s 42% of the U.S. adult population!)

While you can get varying amounts of vitamin C from fruits and vegetables (e.g., oranges, bell peppers, cruciferous vegetables, and kiwis), statistics demonstrate getting the essential vitamin from diet alone is not a foolproof strategy since 46% of U.S. adults are failing to consume just 60 to 75 milligrams of the water-soluble micronutrient daily (i.e., less than baseline daily requirements).

To guarantee you’re getting enough of the key vitamin and to leverage its full array of health benefits, a daily vitamin C supplement (preferably one that delivers an effective dose of vitamin C in a highly bioavailable form) is an effective solution.* 

Stomach discomfort is one of the most common side effect observed by Alexander Michels, Ph.D., clinical research coordinator at Oregon State University’s Linus Pauling Institute. “This is usually because people are consuming the acidic form of vitamin C—ascorbic acid—and for some, their stomach can’t handle the extra acid.”

In addition to personal differences in physiology (as well as stomach sensitivity, presence of a meal, etc.), the potential for stomach issues as a side effect is largely dependent on dose and form of vitamin C, which we discuss in detail here.

Side effects like gas, bloating, and changes in regularity may occur at very high doses of vitamin C. According to Michels, this is most common when megadosing the vitamin (i.e., consuming beyond 2,000 milligrams in a short period of time)—which, for reference, is equivalent to approximately 40 small oranges and at least twice the dose of most high-potency supplements.

General GI concerns, struggling to sleep deeply (perhaps by way of digestive distractions or due to vitamin C’s role in cellular energy production), and flushed skin are other potential side effects, says Christyna Johnson, M.S., L.D., RDN, registered dietitian and host of the Intuitive Eating for the Culture podcast. But even then, Michels reassures that, “For many people, these side effects are mild and transient.”  

As for topical skin care, Michels warns that some products with vitamin C may cause mild irritation—especially if you go out in the sun right after applying them to your skin. Since vitamin C supplements can provide complementary skin health benefits, you can always try vitamin C orally to sidestep or synergize topical approaches. 

Each body is different, and there’s no dose that are definitively linked to side effects for everyone. That’s not how nutrition and our individual genetic makeup works. Michels says that even at the highest doses of vitamin C (again, above 2,000 milligrams daily), side effects often dissipate after a week as the body adjusts.

Johnson also notes that GI concerns typically resolve once the vitamin C has been properly absorbed into the system. Taking a vitamin C supplement with adequate amounts of water can help aid digestion and absorption, as well as minimize the mild side effects that may come when unabsorbed leftovers need to be disposed of (i.e., via urine).

But to further optimize absorption with intention, consider a highly bioavailable form of vitamin C —such as PureWay-C™, a vitamin C-lipid-bioflavonoid complex featured in mbg’s vitamin C potency+.

If side effects persist with vitamin C supplementation or any nutrition regimen, it’s always smart to consult your healthcare provider. 

Vitamin C may be best known as a first line of defense when you’re feeling under the weather (a reactive approach we would highly recommend swapping for a more proactive one), but it plays a number of critical functions and provides a slew of whole-body benefits.* 

“Once you have taken enough vitamin C that you are no longer at risk of deficiency, the remainder goes to antioxidant protection,”* Michels says. This manifests in supporting the immune, cardiovascular, and central nervous systems by delivering broadly protective actions against oxidative stress, or, in Michels’ words, “protecting you from free radicals that we encounter in our daily lives.”*

Here are some specific health benefits you can expect when maintaining sufficient vitamin C status:

Arguably its most famous benefit, vitamin C is well-known as an avid supporter of both innate and adaptive immunity—i.e., the immunity we’re born with and the immune response that’s triggered when unwanted microorganisms enter the body.* 

Vitamin C not only plays a role in the production of white blood cells, but also stimulates the creation of antibodies and helps T cells reach maturity.* 

Researchers studying the link between immunity and vitamin C have found that leukocytes (the umbrella term for white blood cells, including T cells, that help the body fight invading pathogens) use vitamin C to protect themselves from oxidative stress.*

As mbg’s vice president of scientific affairs Ashley Jordan Ferira, Ph.D., RDN, has previously explained, “You can’t even create the immune cells to fight for you without vitamin C.”*

Another buzzworthy benefit of vitamin C is brighter, more youthful-looking skin.* Because the body requires vitamin C to produce collagen—the body’s most abundant protein that makes up skin and all connective tissues—getting enough vitamin C can help enhance skin elasticity (think bouncy, firm skin).*  

But the skin benefits don’t stop there. Topical approaches can go hand in hand (literally). In a 2015 study published by Clinical, Cosmetic and Investigational Dermatology, researchers found that topical vitamin C increased collagen production and made skin brighter in healthy female participants.

According to a 2017 Nutrients scientific review, consuming vitamin C via both food and supplements has been associated with improved skin elasticity and texture, less wrinkling, and enhanced protection from unwanted effects of UV light.* Interestingly, while researchers found that topical vitamin C products demonstrate photoprotective properties against UV light, they noted that ingesting vitamin C may be more effective.* 

Collagen gets a lot of buzz for its skin benefits, but it plays an equally critical role in joint health, supporting everything from joint mobility to musculoskeletal integrity.* Because vitamin C is a necessary prerequisite to collagen synthesis (and let’s not forget the antioxidant benefits of vitamin C for collagen longevity), getting optimal levels of vitamin C is essential to comprehensively support musculoskeletal health.* 

In a 2020 study from The Journal of Nutrition, researchers found higher vitamin C intake among older adults was associated with greater muscle mass, especially in women.* Given the overwhelming scientific evidence that vitamin C levels decrease as we age, achieving sufficient vitamin C status becomes increasingly important later in life to promote whole-body health—and muscle mass and strength are pivotal to physical function and longevity.* 

While vitamin C is a useful, complementary strategy for optimizing iron absorption regardless of your dietary pattern, the synergy becomes even more important for vegetarians and vegans. For those who avoid animal products (especially meat), vitamin C can play a crucial role in ensuring adequate iron absorption.* 

While iron is found in plant-based sources like broccoli and spinach, plants only contain non-heme iron, which is much less bioavailable than heme iron—the kind found solely in animal sources. Luckily, vitamin C can enhance the absorption of non-heme iron, seriously increasing its bioavailability, Johnson explains.*   

Since nearly half of U.S. adults fail to consume minimum requirements of vitamin C daily, it’s unlikely that the average person will overdo it on vitamin C.  

So what are those minimum daily requirements? Per the National Academies, the recommended daily intake of vitamin C is 75 milligrams for women (85 and 120 milligrams if pregnant or lactating, respectively) and 90 milligrams for men, or about 1.5 oranges.

However, those baseline starting levels are debated. Michels says a daily minimum of at least 200 milligrams is actually needed to maximize blood concentrations of vitamin C. He recommends 400 milligrams daily, though evidence suggests that even higher doses can help bolster vitamin C status and promote optimal cardiovascular benefits.*

When it comes to safety, those taking higher potency vitamin C supplements shouldn’t worry—up to 2,000 milligrams of vitamin C daily is considered safe. Beyond that, the side effects listed above may begin to occur, but are generally mild and short lived, Michels says. 

That’s because vitamin C is water soluble, meaning it’s transported through the bloodstream and doesn’t need another mechanism to move around, like a fat-soluble vitamin does. Thanks to vitamin C’s water solubility, “the body can easily remove any excess through the kidneys,” Michels explains. 

For the average person, the most notable interaction to look out for with vitamin C is its potential ability to weaken the effects of certain medications. Michels says that vitamin C can ​​increase excretion of certain products into the urine, which quickens the rate at which it leaves the body and shortens the amount of time you feel its effects. 

Additionally, people with certain health concerns should take extra care with higher-dose vitamin C supplements.

Individuals with renal health concerns should talk to their health care provider before adding a vitamin C supplement to their regimen, since, according to Michels, ascorbic acid can break down into oxalate (too much of which can affect kidney function).

Those taking blood-thinning medications should also speak with their health care provider before taking a new vitamin C supplement, since it may alter its effects.   

Those with very high levels of iron may also want to exercise caution, since vitamin C can increase the amount of iron the body absorbs.

While vitamin C plays a number of critical roles in the body and provides a slew of joint, skin, and immune health benefits, most people don’t get enough of the essential micronutrient, even in these modern times.* A high-quality vitamin C supplement (with bioavailable vitamin C rooted in absorption science and bioefficacy research) is a convenient and effective way to achieve and maintain sufficiency of this pivotal nutrient.* 

Because vitamin C is a water-soluble vitamin, any excess is flushed out with urine. And while side effects may occur at very high doses, they’re likely to be mild. Of course, it’s always smart to check with your healthcare provider when introducing new supplements to your daily routine, or experiencing any unwanted side effects. 

If you’re looking for a science-backed vitamin C supplement with the added benefits of citrus bioflavonoid phytonutrients, check out mbg’s vitamin C potency+ or peruse our list of best vitamin C supplements on the market.*