Vitamin C plays an integral role in the synthesis of amino acid derived carnitine. Vitamin C is involved in the hydroxylation process with carnitine, in which vitamin C functions as the reducing agent, thus losing electrons to then be oxidized in a chemical reaction (Gropper & Smith, 2013). More specifically, it functions by reducing ferric state iron atoms back to ferrous state, via reactions catalyzed by 4-butyrobetaine, hydroxylase, and trimethyllysine hydroxylase (Gropper & Smith, 2013). Sub optimal intake of vitamin C has been linked to alterations in plasma free carnitine levels (Johnston, Solomon, & Corte, 2013). In the presence of low vitamin C intake, 4-butyrobetaine hydroxylase is decreased and 4-butyrobetaine levels rise, which acts as a potent inhibitor of carnitine transport in skeletal muscle (Johnston, Solomon, & Corte, 2013). Thus, plasma carnitine levels may function as a viable index for vitamin C intake status.
Vitamin C always plays several cofactor roles with other reactions including the productions of the hormone thyroxin, which regulates over all metabolic rate (Whitney & Rolfes, 2005). Combination of lower thyroxin levels and plasma carnitine levels affect overall fat metabolism. Carnitine transports long chain fatty acids into the mitochondria of a cell for energy metabolism and short chain fatty acids from inside the mitochondria to the cytosol (Wutzke & Lorenz, 2004). Diminished levels of carnitine will therefore negatively affect fat oxidation.
Sources
Gropper, S.S., & Smith, J.L. (2013). Chapter 9: water-soluble vitamins. Advanced Nutrition and Human Metabolism (6th ed.)(pp.312). Belmont, CA:Wadsworth Cengage Learning
Johnston, C.S., Solomon, R.E., & Corte, C. (2013). Vitamin C depletion is associated with alterations in blood histamine and plasma free carnitine in adults. Journal of the American College of Nutrition, 15(6), 586-591. Doi:10.1080/07315724.1996.10718634
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