We have established that vitamin C has benefit in cancer treatment but the dosage and route of administration is essential determine if it has a direct anti-tumor action or a supportive function. The levels needed to achieve direct tumor killing effects are 200-1000 micromol/L (Chen et al 2007, Levine et al 2011). To achieve higher these higher anti-cancer levels, IV doses of 25-50g are required. 50g of IV vitamin C can achieve a plasma level of over 14,000 micromol/L. Oral supplementation is is not able to get anywhere near those levels since absorption is limited in the digestive tract. Blood vitamin C levels peak after 200mg of oral supplementation and maximal oral dosing before loose stools occur is around 4g (Levine et al 2011). The picture shows the difference in plasma concentration between 200mg of oral or IV vitamin C (Levine et al 2011). Even when using the same 10g dose, intravenous administration achieved a 50-150 times greater plasma vitamin C level compare to oral supplementation (Chen et al 2007, Padayatty et al 2004).
So what does this mean? Get lots of vitamin C throughout the day to keep your blood levels up. You don't need much. One red sweet red pepper gives you over 300mg of vitamin C. Guava, spinach, kale, broccoli and kiwi are also very rich in vitamin C. If you are going to supplement for general health than I recommend 500-1000mg dose 2-3 times daily. If you have a cold, runny nose, canker sore, cold sore or any other infection I would increase the dose to bowel tolerance. That means 1000-1500mg 3 or 4 times a day and keep increasing until you get loose stools. These doses are very safe since the extra vitamin C is just excreted if it isn't used.
However if you really want to have a direct anti-cancer effect you need to use IV treatments done by a trained doctor. In that case you would still take the oral doses on the days you don't get the IV.
So when it comes to vitamin C its all in the dose and the delivery.
Chen et al. Ascorbate in pharmacologic concentrations selectively generates ascorbate radical and hydrogen peroxide in extracellular fluid in vivo. Proc Natl Acad Sci U S A. 2007 May 22;104(21):8749-54.
Levine M, Padayatty SJ, Espey MG. Vitamin C: a concentration-function approach yields pharmacology and therapeutic discoveries. Adv Nutr. 2011 Mar;2(2):78-88.
Padayatty et al. Vitamin C pharmacokinetics: implications for oral and intravenous use. Ann Intern Med. 2004 Apr 6;140(7):533-7.
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