Vitamin C (Vitamin C, abbreviation: Vit. C), since the discovery of scurvy (a series of diseases caused by a lack of vitamin C in the diet), has been widely known and began to be used to maintain health and treat diseases, and daily In daily life, no matter in supermarkets, pharmacies, mass merchandisers, etc., we can see special nutritional products with higher vitamin C content. But is vitamin C better when consumed in higher doses?
Refer to the information provided by the National Institutes of Health (NIH)data, the following is a summary of several key issues:
The higher the dose of vitamin C, the better the effect?
Intestinal absorption of vitamin C is regulated by at least one dose-dependent active transporter, but oral administration of vitamin C produces tissue/plasma concentrations of Strictly controlled by the human body. At moderate intakes of 30–180 mg/day, approximately 70%–90% of vitamin C is absorbed, however, when doses exceed 1000 mg/day, the absorption rate drops below 50% of unmetabolized vitamin C It will be excreted through urine. In terms of pharmacokinetics, oral administration of 1250 mg/day of vitamin C can achieve an average plasma concentration of approximately 135 micromol/L, which is approximately twice the plasma concentration produced by dietary intake of approximately 200–300 mg/day of vitamin C. times, and the model predicts that even if 3000 mg of vitamin C is taken every 4 hours, the peak plasma concentration will only reach 220 micromol/L.
It can be seen that the higher the oral dose of vitamin C, the higher the plasma concentration in the body will be. However, due to the limitations of the oral absorption rate, as the oral dose of vitamin C increases, its absorption efficiency will gradually accelerate and decrease, resulting in a marginal As a result, a large amount of vitamin C is directly excreted through urine and wasted.
What is the [recommended daily intake] of vitamin C?
Recommended Dietary Allowances (RDAs) refer to the recommended dosage that is sufficient to meet the basic health needs of the 97-98% group. The recommended intake of vitamin C varies for different age groups (as shown in the figure below), but generally speaking, the recommended amount can be achieved by consuming sufficient amounts of fruits and vegetables in the diet. However, the so-called "basic health needs" are very vaguely defined. Therefore, for people with diseases, they do not need to take in the amount of vitamin C recommended in the figure below, but need to be evaluated and recommended by a professional physician.
What is the [upper limit intake] of vitamin C?
Tolerable Upper Intake Levels (ULs) refer to doses that are unlikely to produce significant side effects. For different age groups, the upper limit of vitamin C intake is different (as shown in the figure below).
How should I take vitamin C?
In addition to assisting wound healing, having good antioxidant capacity, and regulating the immune system, vitamin C also has the potential to fight against oxidative stress-related diseases (such as cancer, cardiovascular disease, etc.), but in order to make vitamin C like this The intervention of special nutritional products has more targeted effects and takes into account safety. It is still recommended to consult a professional doctor before taking them, so as to avoid spending a lot of money and taking a lot of wrongful decisions.
〈The author is former Attending Physician in National Taiwan University Hospital, and Master of Science from National Taiwan University〉