Cold and Flu Season - The Role of Vitamin C and Sugar

As the winter days drag on, in the United States we find ourselves right in the middle of the cold and flu season. Inevitably, many of us will feel the dreaded scratchy throat, runny nose, or fever. Most people attribute their cold to late nights and being exposed to more germs. However, sugar plays a big role in undermining our immunity because it competes with Vitamin C for the same transport system.

That’s right! The same transporters, GLUT, that carry glucose into our skeletal muscles also carry vitamin C. Unfortunately for us, sugar is more powerful than vitamin C, and the glucose molecules will eventually kick the vitamin C off the transport molecule, thereby lowering our own immunity (1).

From an evolutionary perspective, having the GLUT transporters carry both Vitamin C and glucose made sense as >4000 animals make Vitamin C from glucose (2), but a genetic change now prevents humans from completing the final step in making Vitamin C from glucose (3).

As a result, humans are one of the few animals in the world that do not make their own Vitamin C, meaning we have to obtain Vitamin C through foods or supplements. For a point of reference, goats make ~ 200mg/kg of Vitamin C which means a 70kg goat (average weight of an adult female) will make ~14 grams of Vitamin C, in contrast to 100 mg of Vitamin C in a kiwi fruit.   

Vitamin C is crucial for many things such as: (3) (4)

• Wound healing
• Production of collagen
• Production of catecholamines such as epinephrine
• Increased absorption of iron
• Protect against DNA damage
• Free radical quencher: if you are stressed or smoke, you generate free radicals. Vitamin C neutralizes the free radicals
• Supports the immune system, especially the production of white blood cells

In addition to the GLUT transporter, there is another gene that is involved in Vitamin C transport and regulation in the tissue: SVCT (sodium dependent vitamin c transport) in the SLC23 family. SVCT1 is considered the central transporter that controls Vitamin C levels throughout the entire body (5). Recent research has found that individuals with a variant in SVCT1 (rs4257763) had lower levels of Vitamin C.

Another study looking at 15,000 people found that individuals with a different SVCT snp (rs33972313) lead to lower ascorbate levels across all ethnicities because the gene variation leads to decreased transportation of Vitamin C and increased elimination of Vitamin C  (5). As a result, people who do not take Vitamin C supplementation will obtain very little Vitamin C from their diet, and they will not have adequate Vitamin C levels to support their body.

A second gene that works with Vitamin C is the GST family (glutathione S transferase). GST helps code for glutathione which in turn works with Vitamin C.  One of the major roles of the GST family, specifically GSTM and GSTT is to protect the body from environmental toxins (5).

As a result, individuals with the deletions in these genes are more sensitive to environmental toxins. If there is more oxidative stress occurring in the cell, then it will prevent the oxidation of ascorbate or the reutilization of ascorbate from its oxidized form DHA (dehydroascorbic acid). Research suggests that individuals with lower enzyme production from a GST SNP will have lower glutathione and Vitamin C levels (5). Of note, researchers have found that if people do not take Vitamin C and they have the SNP that codes for the lower enzyme production, they have even lower levels of Vitamin C.  

Take home points: 

• Check your Nutrition Optimization report for your Vitamin C status. If you have a medium or high impact, consider adding in Vitamin C starting at 500 mg twice daily.
• If you have any genetic variations in the SVCT gene and you don’t take Vitamin C, you have a high likelihood of having lower vitamin C levels than people without the variation. 
• People with low Vitamin C levels tend to have weakened immune systems.
• Vitamin C can help protect the body from the free radicals produced by sugar.