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Taking Too Much of This Common Vitamin Could Damage Your Thyroid and Cause Kidney Stones

And it probably won't protect you from a cold.


Vitamin C is a vital nutrient for proper immune and brain health, but people use it for all sorts of reasons. Some to boost collagen production, others swear by it for preventing or treating the common cold (though this isn’t supported by research). While you can never eat too many oranges, there are a few important things you should know about vitamin C in supplement form, and how overdoing it could negatively affect your health.

Effects of Too Much Vitamin C

Vitamin C is a water-soluble vitamin, which simply means that it can dissolve in water. As opposed to fat-soluble vitamins, which get stored in our fat tissue, the water-soluble ones aren’t stored in the body, and excesses are excreted through our urine.

The problem, however, arises when the body becomes overloaded with the nutrient, say, if you’re taking a high-dosage supplement for an extended period of time. Initial symptoms could include digestive upset and diarrhea, which have been seen in doses higher than 2,000 milligrams (mg) per day.

Research also suggests that taking too much vitamin C may harm the kidneys. The reason is that excesses of the nutrient gets excreted through the urine as a waste product called oxalate. When there is a high amount of oxalate in the body, it’s harder for the kidneys to eliminate, and it can bind to other minerals and create kidney stones. Several studies have shown that taking high-dosage vitamin C supplements both increases oxalate levels and increases the risk of kidney stones. One study even linked some cases of kidney failure to vitamin C supplementation, but this is considered rare.

Another side effect of taking too much vitamin C is that it can boost iron absorption specifically of non-heme iron which comes from plant-based foods. While generally this is considered a benefit, high doses can cause iron overload or iron toxicity — a serious condition that can lead to long-term damage to your thyroid, heart, liver, and central nervous system. Yikes!

How Much Is Too Much?

The tolerable upper limit (TUL) of vitamin C has been established at 2,000 mg per day for adults, which means that most adults can tolerate this amount without harmful side effects. All of the studies referenced above found adverse effects at doses higher. That being said, if you have a condition like hemochromatosis, where there’s already an increased risk of iron accumulation in the body, you should talk to your doctor before taking vitamin C supplements. Similarly, if you’re prone to kidney stones, consult your primary care provider about any supplements you’re taking.

One way to ensure that you’re not over-consuming this vital nutrient is to choose supplements and stay at or near the 100 percent daily value. The recommended daily intake for vitamin C for adult women is 75 mg per day. You can also increase your levels by getting more of it in your diet, which typically has no harmful effects on your health. To do it, eat more citrus fruits, peppers, strawberries, kiwis, potatoes, and broccoli.

We hope this helps you make a more informed decision about which supplements you should be taking — and how much!

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