Secrets behind Vitamin C… Is it really good or bad for our health?



Researchers have found that Vitamin C can kill multidrug-resistant tuberculosis (MDR-TB). The hypothesis is that vitamin C killed the bacteria by driving an iron-dependent reaction, which produces reactive oxygen species and induces cell death via DNA damage. One can ask now, if Vitamin C can kill bacteria by damaging DNA, could it harm human cells, too
Oxygen paradox: We all know that the vast majority of complex life on Earth requires oxygen for its existence. However, oxygen can also damage living organisms when present in other forms, for example, hydroxyl radicals. Antioxidants, on the other hand, scavenge these reactive oxygen species and thereby prevent oxidative damage to important biological macromolecules such as DNA, lipids and proteins.
If you quickly search on internet, you will probably come across that Vitamin C, or ascorbic acid, is a very important water soluble vitamin but, our body cannot synthesize it due to lack of an enzyme called gulonolactone oxidase. Hence, ascorbic acid has to be supplemented, for example through fruits, vegetables and tablets. It is known to be a very effective antioxidant for our body.  Ascorbate and ascorbyl radicals react with most biologically relevant radicals and oxidants and it also takes a role in the regeneration of other small molecule antioxidants such as α-tocopherol, glutathione (GSH) and β-carotane. 
So how does Vitamin C kill multi drug-resistant tuberculosis (MDR-TB) bacteria then?Researchers at the Albert Einstein College of Medicine in New York have published a paper recently to show they have found that Vitamin C can kill multidrug-resistant tuberculosis (MDR-TB) in the lab. The hypothesis is that vitamin C killed the bacteria by driving an iron-dependent reaction that produces reactive oxygen species (ROS), which can induce cell death via DNA damage.
This finding can be explained by the pro-oxidant effect of Vitamin C. Reduction of transition metal ions by ascorbate produces free hydroxyl radicals by the reaction of reduced metal ions with hydrogen peroxide; this process is called the Fenton reaction.  These free radicals generated are very powerful, non-selective oxidants, which damage DNA and several other biological compounds, eventually killing the bacteria.
Although Fenton chemistry occurs readily in the laboratory conditions in vitro, levels of free metal ions inside the body are thought to be insufficientfor these reaction pathways because of the presence of metal binding proteins such as ferritin, transferrin and ceruloplasmin. In addition, iron must be in the ferric(III) form to take part in Fenton reaction, but most of the intracellular iron is in ferrous(II) form. Thus, the pro-oxidant effect of Vitamin C most likely arises as a result of the externally provided metal ions in the media, whilst inside the human body Vitamin C still behaves as an antioxidant.
What the paper reveals is obviously an important discovery and as already being speculated, vitamin C could be used alongside TB drugs to cure MDR-TB. However, there should be more studies conducted before legitimate conclusions are drawn about in vivo applications.  
What is TB? How does it spread?
Tuberculosis (TB) is a contagious lung disease that spreads through the air. When people with the disease cough, sneeze, talk or spit, they propel TB germs, known as bacilli, into the air. Only a small number of the bacilli need to be inhaled to cause an infection. However, not all people infected with TB bacilli will become sick. The immune system either kills the germs, or "walls off" the TB bacilli where they can lie dormant for years. Failure of the immune system to control infection with TB bacilli leads to active disease, when TB bacilli multiply and cause damage in the body. Left untreated, each person with infectious TB will spread the germs to about 10 to 15 people every year. World Health Organization
What is multidrug-resistant tuberculosis (MDR TB)?
Multidrug-resistant TB (MDR TB) is caused by an organism that is resistant to at least isoniazid and rifampin the two most potent TB drugs. These drugs are used to treat all persons with TB disease. Centers for Disease Control and Prevention
Vitamin C
Ascorbic acid or "vitamin C" is a monosaccharide oxidation-reduction (redox) catalyst found in both animals and plants. As one of the enzymes needed to make ascorbic acid has been lost by mutation during primate evolution, humans must obtain it from the diet; it is therefore a vitamin. wikipedia
Antioxidant
Antioxidants are body’s natural mechanism to help neutralize free radical. Oxidative stress occurs when the production of harmful molecules called free radicals is beyond the protective capability of the antioxidant defenses. Free radicals are chemically active atoms or molecular fragments that have a charge due to an excess or deficient number of electrons. Examples of free radicals are the superoxide anion, hydroxyl radical, transition metals such as iron and copper, nitric acid, and ozone. Free radicals containing oxygen, known as reactive oxygen species (ROS), are the most biologically significant free radicals. ROS include the radicals superoxide and hydroxyl radical, plus derivatives of oxygen that do not contain unpaired electrons, such as hydrogen peroxide, singlet oxygen, and hypochlorous acid. Because they have one or more unpaired electrons, free radicals are highly unstable. They scavenge your body to grab or donate electrons, thereby damaging cells, proteins, and DNA (genetic material). The same oxidative process also causes oils to become rancid, peeled apples to turn brown, and iron to rust. Howstuffworks
Is it possible to take too much vitamin C?
For most people, a large orange, 1 cup (about 165 grams) of sliced strawberries, chopped red pepper or broccoli provide enough vitamin C for the day. Any extra vitamin C will simply be flushed out of your body in your urine. For adults, the recommended dietary reference intake for vitamin C is 65 to 90 milligrams (mg) a day, and the upper limit is 2,000 mg a day. Although too much dietary vitamin C is unlikely to be harmful, megadoses of vitamin C supplements may cause: Diarrhea, Nausea, Vomiting, Heartburn, Abdominal bloating and cramps, Headache, Insomnia, Kidney stones. Mayo Clinic  by Katherine Zeratsky, R.D., L.D. (nutritionist)
To see foods with highest Vitamin C content visit: http://www.healthaliciousness.com/articles/vitamin-C.php#vitamin-C-rich-foods

Related paper
Mycobacterium tuberculosis isextraordinarily sensitive to killing by a vitamin C-induced Fenton reaction, Vilcheze C., Hartman T., Weinrick B., Jacobs Jr W. R., Nature Communications, 2013,

References
1 ) Vitamin C in human health and disease is stilla mystery ? Naidu K. A., Nutrition Journal 2003, 2:7
2) Vitamin C: antioxidant or pro-oxidant in vivo?  Halliwell B. Free Radic Res. 1996, 25(5):439.
3) Does vitamin C act as a pro-oxidant underphysiological conditions?  Carr A., Frei B. The FASEB Journal , 1999,  13(9):1007

written by 
Abidin Balan       find him on Facebook  Google+ or Linkedin

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Abidin Balan