As the weather here turns colder, thoughts turn to preventing colds and the flu. My “go to” method of preventing sickness has always been by loading up on vitamin C, even though recent studies haven’t really supported the idea that vitamin C increase immune function. Like most nutrients, our genes play a role in how the nutrient is transported and used by the body.
So, what happens when we take or eat vitamin C? Our bodies have vitamin C transporters that are involved in the absorption of ascorbic acid (Vit. C) in the intestines. Most mammals actually make vitamin C themselves, but humans can’t make vitamin C and have to rely on food sources.
Vitamin C has a variety of functions in the body. It is an antioxidant, as well as a co-factor in many important enzyme reactions, including the synthesis of collagen, carnitine, and some neurotransmitters.
There are several major diseases associated with vitamin C levels as well as with genetic polymorphisms of the vitamin C transporters, SLC23A1 and SLC23A2:
- Higher intake of vitamin C is associated with a reduced risk of cardiovascular disease. Higher plasma vitamin C levels (whether due to genetics or due to higher fruit and vegetable intake) is associated with a reduced risk of both heart disease and overall mortality. [ref]
- Higher intake of vitamin C is associated with a reduced risk of stomach cancer.[ref] Stomach cancer is now the third leading cause of cancer deaths worldwide.[ref]
SLC23A1 and SLC23A2 are the genes that code for vitamin C transporters. Variants of these genes affect the plasma levels of vitamin C. All of these variants are very common; some are associated with higher plasma vitamin C concentrations and some with lower concentrations. You can check your 23andMe results for the variants by clicking the link below (if you have received your results after Aug. 2017, use the links that say v.5).
- rs6133175 (v. 4 only): Those with GG have (on average) 24% higher plasma vitamin C concentrations.[ref]
- rs6053005 (v. 5 only): Those with TT genotype allele have (on average) 24% higher plasma vitamin C concentrations.[ref]
- rs12479919 (v. 4 only): The T allele is associated with lower risk of gastric cancer, with those carrying the TT genotype at half the normal risk of gastric cancer.[ref] [ref] Since higher vitamin C levels = lower gastric cancer risk, it makes sense that those people with the T allele will have higher levels of vitamin C.[ref]
- rs33972313 (v. 5 only): Those with a T allele have an average decrease in plasma vitamin C concentration of 24%.[ref] Another study found that those with the C allele have a reduced risk of heart disease (implied that it is due to increased vitamin C transport) [ref]
- rs10063949 (v. 4 and v.5): The C allele is associated with decreased vitamin C transport, and also with an increased risk of Crohn disease [ref]
- rs1776964 (v. 4 only): A study found a higher risk of heart disease in homozygous AA women regardless of vitamin C intake. [ref]
SLC2A1 (also known as GLUT1) is the gene that codes for the enzyme that transports glucose across the cell wall. This same enzyme also transports the oxidized form of vitamin c, dehydroascorbic acid, into cells where it is then reduced to ascorbic acid. [ref] While there are studies linking GLUT1 polymorphisms to diabetes in some populations, I didn’t find any relating to vitamin C levels in the cell.
I did find one interesting study that I wanted to share about vitamin C, glucose, and cancer: A study in 2015 looked at the levels of glucose and ascorbic acid in thyroid cancer cells. “The results showed that in thyroid cancer cells high glucose inhibits both transport of AA [ascorbic acid] and DHAA [dehydroascorbic acid]. Inhibition of vitamin C transport by glucose had a cytotoxic effect on the cells. However, stabilization of vitamin C in one of 2 forms (i.e., AA or DHAA) abolished this effect. These results suggest that cytotoxic effect is rather associated with extracellular accumulation of vitamin C and changes of its oxidation state than with intracellular level of ascorbate.”
Boosting your vitamin C intake:
The US RDA for vitamin C is 60mg per day, which is a little above what is needed to prevent scurvy (46mg/day). The Vitamin C Foundation recommends 3000 mg/day,[ref] and the Linus Pauling Institute recommends 400mg/day. Vitamin C is a water-soluble vitamin and non-toxic, but you (and your bathroom) will know it if you exceed your personal bowel tolerance.
Excellent food sources of vitamin C include oranges, grapefruit, kiwi, strawberries, tomato and red peppers.
There are lots of options for vitamin C supplements including liposomal vitamin C. *
More to read:
Oregon State University: Vitamin C