What Are The Anticancerous Effects of Vitamin C and Vitamin E? (Evidence based article)

What Are The Anticancerous Effects of the antioxidants Vitamin C and Vitamin E?

^{by Alexander Van Dorph (2010)}

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This article goes through the anticancerous/anticarcinogenic properties of the antioxidants Vitamin C and Vitamin E. Is their any evidence that vitamin C and vitamin E can help prevent cancer? Well, yes, the evidence is there, but is it strong enough? Read through the article and give my your opinion on the matter, please.

Vitamin C

Vitamin C, also known as ascorbic acid, is a water-soluble antioxidant. Unlike most mammals, humans are not able to synthesise their own vitamin C, and therefore need to absorb it through the diet (Higdon 2006). Vitamin C has several functions. It is required for collagen synthesis, which is an essential structural component for blood vessels, tendons, ligaments and bone (Carr et al 1999). Another important function of vitamin C is its role in norepinephrine synthesis, which is a neurotransmitter essential for brain function and which also, has shown to affect mood. Ascorbic acid is well known for its antioxidant properties and its ability to scavenge free radicals. (Padayatty et al 2003)

Vitamin C – Antioxidant Function

Vitamin C is called an antioxidant because, by donating its electrons, it prevents other compounds from being oxidized. By forming ascorbate, an ion of ascorbic acid, it is able to react with a reactive and possibly harmful free radical, thus reducing it to a less reactive compound. (Read my article on The Free Radical theory if you are unsure what a free radical is) Schorah et al (1996) found that the plasma concentration of ascorbic acid was lower in critically ill patients compared to healthy subjects; this could be linked to ascorbic acid’s role as a free radical scavenger. McGregor and Biesalski (2006) found that increasing the plasma concentration of ascorbic acid in individuals with high levels of oxidative stress might have therapeutic effects. To back up these results, it was also found that these individuals have a higher pharmokinetic usage of ascorbic acid.

Research and Studies

Bjelakovic et al (2009) analyzed 33 trials in a Cochrane intervention review, concluding that vitamin C used singly or in combination with other antioxidants had no significant effect on mortality. However, this systematic review included a wide array of diseases, and was not exclusively aimed at cancer. It was also stated that there is a need for future randomised trials to evaluate the potential effects of vitamin C for primary and secondary disease prevention. Jenab et al (2006) demonstrated in a prospective study, which evaluated the European Prospective Investigation into Cancer and Nutrition (EPIC-EURGAST), an inverse association between high levels of vitamin C within the plasma and the risk of gastric cancer.

Vitamin E

Vitamin E is considered the major lipid-soluble antioxidant, it is also the generic term for tocopherols and tocotriols, in which -tocopherol has proven to have the highest biological activity (Brigelius-Fluhe et al, 1999). Traber et al (2007) showed that dietary vitamin E is absorbed and delivered to the liver, in which only -tocopherol is recognised by a protein and transferred to the blood plasma, whereas the other types of vitamin E (i.e. gamma-tocopherol and tocotriols) were removed from circulation, thus acting as the main regulator of all forms of vitamin E. The study further showed indications that the liver is the main site of vitamin E metabolism and excretion.

Functions

The most important function of vitamin E is inhibiting the production of reactive oxygen species during lipid peroxidation (Traber 2006). However, the widely accepted role of vitamin E as a lipophilic antioxidant has been questioned. This is based on findings which suggests that ”…vitamin E on biomarkers of oxidative stress in vivo is inconsistent and metabolites of vitamin E having reacted as an antioxidant are hardly detectable” (Brigelius-Flohe 2009). Vitamin E has been linked to other functions besides its role as a free radical scavenger; these include the inflammatory response and cellular trafficking.

In previously published research, Diplock (1997) stated that there are five different mechanisms in which vitamin E acts upon lipid peroxidation; “(1) decreases local oxygen concentrations, so that oxidation is less likely to occur (2) prevents chain initiation by scavenging the initiation of free radicals (3) binds transition metal ion catalysts to prevent the generation of initiating free radicals (4) decompose peroxides so that they cannot be converted to further active radical species (5) breaks chains to prevent continued hydrogen abstraction by active free radicals.

Research and Studies; The SELECT trial.

One of the biggest human cancer prevention trials conducted in modern time, entitled Selenium and Vitamin E Cancer Prevention Trial (SELECT) was completed in 2008, after having been started in 2004 (National Cancer Institute 2008). Its aim was to assess the role of vitamin E and selenium in the prevention of prostate cancer. The SELECT trial concluded that there were no observable decline in prostate cancer incidence linked with vitamin E and selenium intake. As the 35000 male subjects who took part in the trial did not show improvement based on findings by independent reviewers, the trial conductors chose to discontinue the trial. Bjelakovic et al (2009) analyzed 54 trials in a Cochrane review, concluding that vitamin E used singly or in combination with other antioxidants had no significant effect on mortality; however this systematic review also included other diseases besides cancer making the findings less significant to this review.

^References:

^{Bjelakovic, G., Nikolova, D., Simonetti, RG., Gluud, C. (2008) Antioxidant supplements for preventing gastrointestinal cancers. Cochrane Database Syst Rev. 2008 Jul 16;(3)}

^{Bjelakovic, G., Nikolova, D., Gluud, LL., Simonetti, RG., Gluud, C. (2009). "Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases". Cochrane Database Syst Rev (2): CD007176.}

^{Brigelius-Flohé, R. (2009) Vitamin E: The shrew waiting to be tamed. German Institute of Human Nutrition Potsdam-Rehbruecke, Department of Biochemistry of Micronutrients. (2009)}

^{Brigelius-Flohe, R. (1999). "Vitamin E: function and metabolism". The FASEB Journal. 1999;13:1145-1155.}

^{Carr, AC., Frei, B. (1999) Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. Am J Clin Nutr. 1999;69(6):1086-1107.}

^{Diplock, A.T. (1997). Will the “good fairies” please prove to us that that Vitamin E lessens degenerative diseases? Free Radical Research. Jun; 26 (6), 565-83.}

^{Higdon, J., Ph.D. (2006). Vitamin C. Oregon State University, Micronutrient Information Center. Available from: http://lpi.oregonstate.edu/infocenter/vitamins/vitaminC [Accessed 17th October 2009]}

^{Jenab, M., Riboli, E., Ferrari, P., Sabate, J., Slimani, N., Norat, T., Friesen, M., Tjønneland, A., Olsen, A., Overvad, K., Boutron-Ruault, MC., Clavel-Chapelon, F., Touvier, M., Boeing, H., Schulz, M., Linseisen, J., Nagel, G., Trichopoulou, A., Naska, A., Oikonomou, E., Krogh, V., Panico, S., Masala, G., Sacerdote, C., Tumino, R., Peeters, PH., Numans, ME., Bueno-de-Mesquita, HB., Büchner, FL., Lund, E., Pera, G., Sanchez, CN., Sánchez, MJ., Arriola, L., Barricarte, A., Quirós, JR., Hallmans, G., Stenling, R., Berglund, G., Bingham, S., Khaw, KT., Key, T., Allen, N., Carneiro, F., Mahlke, U., Del Giudice, G., Palli, D., Kaaks, R., Gonzalez, CA. (2006). Plasma and dietary vitamin C levels and risk of gastric cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC-EURGAST). Carcinogenesis. 2006 Nov;27(11):2250-7.}

^{Padayatty, SJ., MRCP., PhD, Katz, A., MD, Wang, Y., MD, Eck, P., PhD, Kwon, O., PhD, Lee, JH., PhD. (2003). Shenglin. Journal of the American College of Nutrition, Vol. 22, No. 1, 18–35.}

^{Schorah, CJ., Downing, C., Piripitsi, A. (1996). Total vitamin C, ascorbic acid, and dehydroascorbic acid concentrations in plasma of critically ill patients. American Journal of Clinical Nutrition 1996; 63:760–765.}

^{Traber, MG. (2007). Vitamin E regulatory mechanisms. Annu Rev Nutr 2007;27:347-62.}