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Surprising Side Effects of Taking Vitamin C Supplements, Says Science

People take vitamin C supplements for a variety of reasons, and here's what can actually happen to your body by doing so.
FACT CHECKED BY Olivia Tarantino

Vitamin C is one of the most popular supplements in America, with surveys showing anywhere between 28 and 34.5% of the population reportedly consuming it regularly. The water-soluble vitamin is a powerful antioxidant that acts as a building block for collagen, helps with wound healing, and also plays a role in immune function. Since the beginning of COVID, even more folks have been popping vitamin C supplements due to the vitamin's link to immune support.

Taking vitamin C supplements may help with some health issues; however, there are some adverse reactions that can happen when you take too much vitamin C in supplement form (as opposed to eating vitamin-C-rich foods).

How much vitamin C should you take? The recommended dietary allowance (RDA) for vitamin C is 75 milligrams and 90 milligrams per day for women and men aged 19 years and older, respectively. The tolerable upper limit for both men and women is 2,000 milligrams per day. If you're taking more than that, discuss with your doctor or registered dietitian.

Read on to discover six side effects you can experience when taking vitamin C supplements, and for more healthy tips, check out 11 Supplements That Dietitians Actually Take.

Gastrointestinal issues

vitamin c supplements

The most common complaint when taking vitamin C supplements is gastrointestinal issues. These include everything from diarrhea to nausea to abdominal cramps. If you find that the supplement affects you in this manner, then consult your physician or registered dietitian.

 9 Worst Supplements for Weight Loss

Kidney stones

supplements and vitamins

Some research shows that vitamin C plays a role in the development of kidney stones. However, the results are conflicting. Research does show that folks who take vitamin C supplements with a pre-existing condition called hyperoxaluria, a condition that happens when there is too much oxalate in the urine, can develop kidney stones. However, this may not be as much of a concern if you don't have these health issues.

Iron overload


Vitamin C helps absorb non-heme iron, which is the iron from plant foods like dark leafy green vegetables. In healthy adults, this doesn't seem to be an issue (in fact, it's actually a benefit—especially for non-meat eaters who get their iron from plants); however, in folks with a condition called hemochromatosis, which leads to the body storing too much iron, high amounts of vitamin C from supplements can worsen the iron overload and damage the body.

 The 18 Best Iron-Rich Foods You Can Eat

Shorter time experiencing a cold

woman taking a multivitamin

Research shows that taking vitamin C supplements may help shorten the duration of the common cold and may also help lessen some of the symptoms.

 10 Places You're Most Likely To Get RSV, According to a Doctor

Dental erosion

Vitamin C on wooden table

If you take lots of chewable vitamin C tablets, you may experience dental erosion of the enamel. Dental erosion can occur when teeth are exposed to an agent like vitamin C frequently and for a long period of time, and it can lead to damage of the teeth.


vitamin c

Taking too much vitamin C in supplement form can affect your sleep. Studies show that adverse side effects of vitamin C supplements include headache, fatigue, sleepiness, and even insomnia.

Toby Amidor, MS, RD, CDN, MS, RD, CDN
Toby Amidor is an award winning dietitian and Wall Street Journal best-selling cookbook author who believes healthy and wholesome can also be appetizing and delicious. Read more about Toby