Amount of Evidence: Very High Potential Benefits: Reasonable Safety: Very High
TABLE OF CONTENTS
What is vitamin C?
This water-soluble essential vitamin is one of the most widely used supplements on the market, most commonly used to support the immune system and prevent common colds. Although it appears ineffective in this regard, it may be worthwhile to include ascorbic acid in your supplement stack. In this article, we will look at vitamin C’s main benefits, potential side effects, and how to use it the right way.
Potential benefits
It is important to note that all of the potential benefits mentioned below are dose-dependent. In general, the higher the dose you take, the more pronounced the effects will be. However, they do reach a plateau at a certain point. We will discuss the best dosing protocol later in this article.
Major benefits
Correcting a vitamin C deficiency – Oral supplementation has been shown to increase plasma vitamin C levels. Therefore, correcting a potential ascorbic acid deficiency is the most important benefit. In severe cases, scurvy is the most dangerous symptom of vitamin C deficiency. However, more common symptoms include weak joints, weak bones, and skin problems. All of this is due to ascorbic acid’s ability to help form new collagen molecules and replace damaged ones. Vitamin C also helps protect existing collagen from oxidation. You can find a list of the symptoms of deficiency later in the article.
Minor benefits
Increased blood flow – As an antioxidant, vitamin C reduces the oxidation of nitric oxide, which keeps your nitric oxide levels elevated and increases blood flow. This effect is most noticeable in people whose blood flow is already impaired, such as diabetics and smokers. But even for these people, the benefit seems relatively insignificant.
Reduction in CRP (C-reactive protein) – This effect, while minor, seems to be very consistent in studies done on ascorbic acid.
Decreased muscle soreness – When vitamin C is taken before exercise, it has been shown to reduce muscle soreness the next day.
Lower blood glucose – There appears to be a slight reduction in fasting blood glucose levels after taking ascorbic acid. However, the scientific studies on this are inconsistent, and more research is needed to prove this effect.
Decreased general oxidation – Unfortunately, this effect is not as significant for many other antioxidants. Some studies even show no difference at all.
Shorter duration of sickness – This benefit appears to be limited to those who take vitamin C regularly and did so before becoming ill. The most common illness for which ascorbic acid is used is the common cold, and there appears to be a 10-20% reduction in the amount of time you are sick. The effects of ascorbic acid on other infectious diseases are not yet clear.
Decreased lipid peroxidation – Although ascorbic acid may reduce lipid oxidation in your body, the effect is minor. Some studies show no effect.
Antioxidant enzymes – A small increase has been observed in the elderly.
Increased bone mineral density – Vitamin C, as well as other antioxidants, protects our bones from losing mineral density as we age. Like most of the other benefits, this effect is small.
Unproven benefits
The effect of vitamin C on these parameters is either not sufficiently researched or the science shows little to no efficacy in these areas.
The intensity of common colds – Vitamin C does appear to shorten the duration of the common cold and some other illnesses but has no significant effect on the severity or intensity of symptoms.
Cancer prevention – Ascorbic acid supplements may or may not be effective for preventing certain types of cancer. Further research on this topic is on the way.
Lower blood pressure – This effect has been demonstrated only in type 2 diabetics, and even then the evidence is mixed.
Cholesterol – There is no significant change in LDL or HDL cholesterol levels.
Triglycerides – No influence on fasting or postprandial triglycerides was ever noted.
Inflammation – Vitamin C has no noticeable effect on inflammation.
Protection from smoking – The only way ascorbic acid could reduce the risks associated with smoking is by increasing blood flow in smokers. Otherwise, it does not protect against the side effects of smoking. However, smoking may increase your need for ascorbic acid by about 35 mg per day, depending on how much you smoke.
Insulin – There may be a slight decrease in fasting insulin but the evidence is mixed.
HbA1c – Ascorbic acid does not appear to influence HbA1c levels in a significant way.
Cortisol – Vitamin C supplements do not affect resting cortisol. However, there may be both an increase and a decrease in the cortisol spike after exercise, depending on several factors.
Rate of sickness – People who take vitamin C are just as likely to get sick as people who do not.
Reduced fatigue – This effect was only seen in obese adults when vitamin C was combined with exercise.
Decrease in heart rate – A slight reduction has been noted in obese adults. However, if you are a healthy individual, it is unlikely that you will notice any effect.
Aerobic exercise – Vitamin C has no significant effect on aerobic exercise performance.
Body fat – So far there have only been 3 studies looking at this effect but none of them has shown any benefit of ascorbic acid for fat loss.
Protection from DNA damage – Ascorbic acid does not appear to protect DNA from damage.
Possible side effects
These side effects are dose-dependent and the risk for them increases (most often linearly but sometimes exponentially) as you increase the dose. Some of the side effects are only relevant to very high doses.
Lower exercise adaptation – Ascorbic acid may speed up recovery from exercise, but it is also likely to decrease exercise adaptation. This effect is also true for most other antioxidants. However, it is important to note that this effect is minor and often exaggerated.
Oxalate nephrotoxicity – This potentially fatal condition can be caused by very high doses taken intravenously.
Diarrhea – This effect often happens to people when they take 4-10 grams of ascorbic acid in a day. Diarrhea induced by vitamin C supplements is not dangerous as long as it doesn’t lead to dehydration which it rarely does.
Kidney stones – While this is not yet supported by scientific research, high doses can generate a compound known as oxalate, which can lead to the formation of kidney stones.
Dental erosion – One meta-analysis found a 16% increased risk of dental erosion when taking vitamin C chewables.
Who should not take vitamin C?
You should probably avoid taking high doses of vitamin C if you:
prioritize exercise performance and muscle growth
are pregnant (high doses of ascorbic acid might increase the potential for miscarriage)
are on a tight supplement budget (even though vitamin C supplements are cheap, there are many more cost-effective supplements on the market, assuming you are getting a good amount of vitamin C from food)
have iron overload (also known as hemochromatosis – because ascorbic acid increases the absorption of iron)
Who will benefit the most?
You should definitely consider taking vitamin C if you:
have symptoms of vitamin C deficiency
are on a carnivore or ketogenic diet
don’t eat fruits or vegetables
are under a lot of physical and mental stress
overtrain
Forms of vitamin C
All of the 5 forms below can be labeled as “Vitamin C” and they all have similar properties in the body. The differences are minor.
Ascorbic acid – This is the form found in most supplements and it is the form naturally occurring in food. Therefore, the bioavailability and effects are identical as if you were to get vitamin C from your diet.
Sodium ascorbate – This form may be a little cheaper than ascorbic acid, but there is not as much research on it. Since ascorbic acid is already quite inexpensive, there is little to no reason to take sodium ascorbate instead.
Potassium ascorbate – Has similar properties to those of sodium ascorbate
Calcium ascorbate – Appears to be slightly more bioavailable, although, like sodium ascorbate, this form has not been researched enough to know for sure what its long-term effects are.
Ascorbyl palmitate – This form seems to be slightly DNA-protective while the other forms could cause oxidative stress to DNA cells. The main drawback is that Ascorbyl-6-Palmitate is not water-soluble.
Signs of vitamin C deficiency
The most common symptoms of deficiency include:
scurvy
weak, painful, or swollen joints
weak bones
dry skin
rough skin
fatigue
irritability
depression
bleeding
impaired wound healing
gum and dental problems
Keep in mind that these signs are just indications of deficiency. The fact that you experience some of them does not necessarily mean that you need more vitamin C. On the other hand, some people may have a deficiency even though they are completely asymptomatic.
With that said, if you experience many or most of these symptoms, there is a high chance you are not getting enough vitamin C. The more of these symptoms you experience and the more severe they are, the more likely you are deficient.
How much vitamin C should you take?
The RDA (recommended daily allowance) for vitamin C is 90 mg. This is, in most cases, enough to prevent symptoms of deficiency. However, there is a case to be made that the recommended daily dose for optimal body function should be around 150 mg.
If you are consuming less than 150 mg daily in your diet, supplementing ascorbic acid to reach this daily optimum will certainly do more good than harm. The closer you already get to 150 mg with your diet alone, the less important it is to take supplemental vitamin C becomes.
As a general rule of thumb, if you consume more than 120 mg of vitamin C daily from food alone, you do not need to worry about supplementation. If you consume less than that, adding ascorbic acid to your stack is worth the consideration. If you get colds frequently, 200 mg daily is probably a safer choice than 150 mg for optimal immune function.
Physical and mental stressors can also increase your vitamin C needs. Smoking, for example, increases your need by about 35 mg daily, depending on how much you smoke.
Megadosing ascorbic acid (taking over 500-4000 mg per day) is just a waste of money in most cases. While the most important and often the only notable side effect is reducing your adaptations to exercise, the benefits are so small that they may not even outweigh this one small negative.
Very high doses (4+ grams), while not toxic, can cause diarrhea and lead to the formation of kidney stones in some people. There is no reason to ever take such high doses. So once you get enough ascorbic acid to prevent a deficiency, there is little to no reason to take additional vitamin C. There are many more effective supplements on the market for whatever your goal is.
Food sources of vitamin C
Fruits and vegetables are undoubtedly the richest food sources. Other food groups rarely provide adequate amounts.
Cruciferous vegetables, radishes, and leafy greens appear to have the highest levels of ascorbic acid out of all vegetables. As for fruits, kiwis, berries, and citrus fruits are generally the best sources.
The easiest way to find out how much ascorbic acid (and other nutrients) you are getting in your diet is with Cronometer.com – the app is free and allows you to track all vitamins, minerals, and more.
Best time to take vitamin C
Since ascorbic acid is water-soluble, it does not matter if you take it with or without food. The time of day does not matter much either, as the half-life of vitamin C is 10-20 days.
The main thing to consider is whether or not you want to take the supplement close to your exercise session. Vitamin C is a double-edged sword because it can speed up recovery but also reduce the body’s ability to adapt to exercise.
Therefore, supplementing close to your workout is usually not a good idea if you wish to maximize the benefits of exercise. The only exception to this rule is if you are overtraining.
Interactions with other supplements
Iron Ascorbic acid has been shown to increase iron absorption. It also partners with iron (and copper) in many functions.
Zinc Absorption of zinc increases when taken with vitamin C. Ascorbic acid also reduces the zinc-binding effect of phytic acid.
Vitamin E Vitamin C protects tocopherols (components of vitamin E) from oxidation.
Thiamine, riboflavin, and niacin These B vitamins provide energy for ascorbic acid to act as an antioxidant. One problem with combining niacin (both nicotinic acid and niacinamide) with ascorbic acid is that ascorbic acid can decrease the absorption of niacin.
Nitrates Nitrates are found in large amounts in green leafy vegetables and beet. As an antioxidant, vitamin C reduces the oxidation of nitric oxide (which is formed by nitrates), keeping your nitric oxide levels elevated, resulting in an increase in blood flow.
Warfarin High doses of ascorbic acid may reduce the effects of warfarin.
Where to buy vitamin C
Amazon seems to be the best option for ordering vitamin C supplements in most countries. They offer some very affordable products that are backed by many positive reviews. Also, you can choose from a wide range of brands there without having to spend time searching through other markets on the Internet.
One thing you should pay attention to is that some brands display the dosage per serving and not per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.
FAQ
Ascorbic acid can be taken daily and does not need to be cycled.
Yes. Vitamin C doesn’t impact your sleep in any negative way.
Fortunately, ascorbic acid and other forms of vitamin C are all very stable molecules that do not lose their effectiveness as long as they do not come in contact with high heat or moisture.
Keep your vitamin C supplements in a cold, dark, and dry place and they will remain just as potent for many years.
There are 2 primary functions of vitamin C related to your skin. First, it helps your body form new collagen molecules and replace the old and damaged ones in your skin with new collagen.
The second function is that vitamin C prevents this fresh collagen from oxidative stress and damage.
It can reduce the redness and swelling associated with acne. This has to do with vitamin C’s ability to protect collagen cells from oxidative damage. The 150 mg daily mentioned earlier should be more than enough for this function.
Even very high doses (over 4 grams) are not toxic but they can cause diarrhea and the formation of kidney stones in some people. There is no reason to take such high doses.
No, it is a water-soluble vitamin. This means that you do not need to take vitamin C and dietary fat at the same time to absorb it well.
No. Vitamin C and calcium are two different nutrients.
Doses under 1 gram won’t make you pee more. Doses over 1 gram could have this effect to help your body excrete the extra vitamin C but it is nothing to worry about.
No. There is little to no anecdotal evidence for this, let alone scientific evidence.
No, it doesn’t. The supplement does not interfere with fasting in any notable way.
References
Most of the information provided in this guide is based on scientific research that can be found and verified in the PubMed medical library. We excluded from consideration studies that are either confounded or have a high conflict of interest.
Anecdotal evidence (from reports on Reddit, YouTube, and other sources) is also taken into account unless it contradicts scientific research.
