Join the NBI Loyalty Rewards Program

How to Take Vitamin C To Bowel Tolerance

Anxiety Word Cloud

By Dr. John Neustadt

Your immune system is an intricate network of specialized organs, cells, proteins, and chemicals. It protects you from an endless onslaught of disease-causing bacteria, viruses, fungi, and parasites, as well as rogue cells that could turn into cancer. More than 50 years of research have shown vitamin C plays a crucial role in various aspects of the immune system. 

The amount of oral vitamin C someone can tolerate depends on the person and their health. Studies indicate that when someone gets an infection, their ability to absorb vitamin C increases. This is because the body uses up a lot more vitamin C when it’s under stress and is an example of how your physiology adapts to meet your body’s needs. This phenomenon of increased vitamin C absorption is often called “to bowel tolerance,” and it’s a technique I shared with many of my patients.1-3 

Vitamin C is safe, even at high doses. When taken orally, if someone gets too much vitamin C, it creates diarrhea. This happens because the amount of vitamin C exceeds the ability of the small intestines to absorb the nutrient. At that point, you’ve reached bowel tolerance and simply need to decrease the amount of vitamin C to the dose that doesn’t cause loose stool.

To Bowel Tolerance

If you’re starting to feel a bit under the weather, or know you’re already fighting something, try this technique to promote a healthy immune system. 

Currently, there is no best test to know how much vitamin C you need. One way to estimate it, however, is based on your bowel tolerance.  Here’s how you determine it.

      • Begin by taking 1000 mg of Vitamin C per day, which is one capsule of NBI’s Vitamin C 1000.
      • The next day, take 1000 mg of vitamin C twice a day, for a total of 2000 mg.
      • The next day, add another capsule, increasing your dose to 3000 mg of vitamin C. You can try this by taking two NBI Vitamin C capsules in the morning and one at night.
      • The day after that, add another 1000 mg. You can take two NBI Vitamin C capsules in the morning and two at night, for a total of 4000 mg for the day.
      • Continue adding one capsule a day until you experience loose or burning stools. At this point, you’ve reached your tolerance of vitamin C and have taken a bit too much.
      • Decrease your dosage of vitamin C one capsule (1000 mg). If loose stools do not reoccur, this is your maximal dosage of vitamin C.
      • If loose stools continue, decrease your dosage of vitamin C until they stop. 

Keep in mind that if you try this when you’re sick, your need for vitamin C may decrease as you recover. You will then experience bowel tolerance at a much lower dose. You will need to slowly lower your dosage until you find your new maximum dosage of vitamin C.


1 Cathcart RF. 1980;9(4):9-13. 

2 Cathcart RF 1986;21(3):307-21. 

3 Holford P, Carr AC, Jovic TH, et al. 2020;12(12).

Top Nutrients for Brain Health

Top Nutrients for Brain Health

Over the next two decades, 20% of all Americans will be over 65 years old. That’s 72 million people, and the majority of those folks will live well into their 90s. Chronic diseases increase with age, including heart disease, depression, osteoporosis, and cancer. But one of the scariest declines of all to contemplate is losing your mind. Forgetting names, faces, your loved ones, or even how to cook and take care of your basic needs. Fortunately, nutrients have been shown in clinical trials to promote the brain, including significantly improving memory and mood.

Vitamin K for Bone, Brain, Immune and Liver Health

Vitamin K for Bone, Brain, Immune and Liver Health

MK4 is a specific form of vitamin K2. And while MK4 is best known for bone health, it’s an important nutrient used throughout your body. Among all the forms of vitamin K2, only MK4 has been shown to maintain strong bones; support brain, liver, and immune health; and promote healthy bone marrow and blood cell production.

Six Surprising Benefits of Vitamin D

Six Surprising Benefits of Vitamin D

Vitamin D does a whole lot more than support healthy bones. Vitamin D supports brain health, muscle size and strength, heart health, mood, pancreas health and insulin balance. This blog discusses six surprising benefits of vitamin D and six more reasons to make sure you get enough of this powerful nutrient.

Share This