Vitamin C, ascorbic acid, is an essential water soluble requirement for our body. Our body is not capable of making Vitamin-C & we need to obtain it from our diet. Vitamin C plays an important role in our bodily processes & is useful in producing collagen- the main structural protein of tendon, ligaments & skin, which protects against oxidative stress & produces neurotransmitters.
Vitamin-C acts as a cofactor for many enzymes. Cofactors are substances that enable various enzymes to function effectively & carry out chemical reactions in the body. The enzymes that uses Vitamin-C as a cofactors are involved in:
- Synthesis of collagen: Collagen is a protein that gives bones, tissues, ligaments, skin, muscle tendons & other connective tissues a structure. Two enzymes involved in synthesis of collagen include prolyl hydroxylase and lysine hydroxylase. If someone fails to consume enough Vitamin-C in their diet, it can impair production of collagen & can cause weakening of bones, skin, blood vessel cells & other connective tissues. Therefore if someone consumes less than 10 mg of vitamin C per day, it can lead to symptoms such as bleeding & poor wound healing.
- Synthesis of Carnitine: Carnitine is an essential amino acid that plays an important role in production of energy from fats. It helps to move fatty acids into mitochondria. Once inside the mitochondria, they can be used as a fuel to generate chemical energy in the form of ATP. This process is called beta oxidation. Enzymes-trimethyllysine hydroxylase and γ-butyrobetaine hydroxylase used in synthesis of carnitine require Vitamin-C as a cofactor. As such Vitamin-C is essential to generate energy from fats.
- Synthesis of Noradrenaline: Noradrenaline is an example of a neurotransmitter- a chemical that transmits signals between nerves. It is one of the key neurotransmitters in our sympathetic nervous system. In the brain & central nervous system, noradrenaline is used by networks that facilitate arousal & attention. Enzyme dopamine β-monooxygenase which converts Dopamine into Noradrenaline, uses Vitamin-C as a cofactor.
- Gene expression: The process by which genes are switched on & off is called gene expression. When the gene is switched on, DNA instructions are read & proteins they code are produced. Many genes that act to switch off genes use Vitamin-C as cofactor. Therefore Vitamin-C has huge impact on gene expression
- Antioxidant: Vitamin-C acts as an antioxidant that helps to neutralise highly reactive substances called free radicals. Vitamin-C neutralises/reduces the impact of free radicals by donating electrons to these harmful substances. This protects important molecules such as DNA, proteins & lipids from damage. Vitamin-C also helps in generating another Antioxidant, Vitamin-E. By preventing accumulation of free radicals, Vitamin-C helps in reducing oxidative stress.
Amount of Vitamin-C in our tissues & bloodstream is tightly regulated. The following process impacts the level of Vitamin-C in our body.
- Intestinal absorption: Vitamin C obtained from our diet does not need to be broken down before it is absorbed. We generally absorb Vitamin C in our intestines. Cell lining (enterocytes) inside our intestines have some specific transport proteins that move Vitamin-C from lumen into the bloodstream. One of the main transport proteins present in our intestines is SVCT1, sodium dependent vitamin C transporter 1. This moves Vitamin C along with sodium ions into enterocytes. Vitamin C that has been transported to enterocytes passes into the bloodstream. When we consume from 30 mg to 150 mg of Vitamin C, around 80% is absorbed. However, if we consume in excess of 1 gram only 50% is absorbed. However, please remember that high intake of Vitamin-C can result in high amounts of unabsorbed Vitamin-C within the intestines & gastrointestinal tract which can cause digestive discomfort, abdominal cramps & nausea.
- Tissue transport: Once in bloodstream, Vitamin C can be distributed to various tissues in the body such as brain, skeletal muscle, liver & adrenal glands. The cells of these tissues have another specific transporter protein SVCT2 that transports Vitamin C into cells. After being moved to cells, Vitamin-C can be used to produce collagen.
- Renal Reabsorption: Kidney is used to filter the blood & flush out waste products in urine & reabsorbing substances that our body needs. Vitamin-C is one such substance that is filtered out & reabsorbed into the blood. This process is vital in regulation of stable vitamin-C levels in the bloodstream & makes Vitamin-C available for other tissues.
SLC23A1 is the gene that codes for SVCT1 protein. This protein is responsible for absorption & reabsorption of Vitamin-C in intestines & liver respectively. Some variations of SLC23A1 gene can negatively impact function of this protein & can reduce the renal reabsorption of Vitamin C. This can impair the kidney & lower the blood plasma level of Vitamin-C, thereby reducing the supply of Vitamin-C to various connective tissues. Such rare variants are present in only 10% of the total population. Common variants of this gene are present in around 35% of the population. However please remember that the frequency of variants of this gene varies among different ethnic populations.
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