Vitamin C

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Vitamin C (ascorbic acid) is an essential nutrient mostly known as a potent anti-oxidant, inhibiting oxidative damage and supporting the immune system. It also facilitates iron absorption, and the conversion of cholesterol to bile acids. Additionally, vitamin C is involved in the synthesis of carnitine, collagen, norepinephrine, and adrenaline and is essential for skin, bone, teeth and cartilage. Acute, persistent lack of vitamin C can lead to scurvy, a rare condition these days. 

 

An inverse relation has been observed between serum ascorbic acid concentrations and several markers of chronic disease, including glucose homeostasis, blood pressure, oxidative stress, high-sensitivity C-reactive protein, and indicators of obesity such as body mass index (BMI) and waist-to-hip ratio. Serum ascorbic acid is also inversely associated with risk of cardiovascular disease, diabetes, cancer and all-cause mortality.

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Diet, age, sex, smoking, body weight, physical activity, and season are all known determinants of serum vitamin C levels. In addition, studies show that there is a substantial genetic factor predisposing for deficiency.

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Individuals with a GSTT1 gene variant show on average a 40% reduction in vitamin C compared to others, even when dietary intake and all other determinants are equal.

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Gene: GLUTATHIONE S-TRANSFERASE, THETA-1 (GSTT1)

Genomic coordinates (GRCh38): 22:17,400,000-25,500,000

 

The GSTT1 enzyme is involved in antioxidation processes. A deletion polymorphism in GSTT1 leads to lack of enzyme activity and has 2 alleles: GSTT1*0 (nonfunctional) and GSTT1*1(functional). The GSTT1*0 variant was associated with lowered absorption of vitamin C.

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Among individuals who did not meet the Recommended Dietary Allowance for vitamin C, the GSTT1 null genotype had an increased risk of deficiency, showing 40% less vitamin C than controls:

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Gene: SOLUTE CARRIER FAMILY 23 (NUCLEOBASE TRANSPORTER), MEMBER 1 (SLC23A1)

Genomic coordinates (GRCh38): 5:139,367,195-139,384,552

 

The absorption of vitamin C into the body and its distribution to organs requires the sodium-coupled vitamin C transporter SVCT1 (aka SLC23A1). SVCT1 is largely confined to epithelial surfacesof the intestine and kidney, and is involved in dietary absorption and renal reabsorption of vitamin C. 

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Vitamin C supplementation is important for subjects with the unfavourable genetic makeup. Individuals under oxidative stress have an even greater need. Smokers need to consume 35 mg/day more dietary vitamin C to make up for.

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People who hardly consume vegetables and fruits, or having a condition that reduce ability to digest and absorb food (such as Crohn's disease and ulcerative colitis) need to supplement vitamin C. Pregnant and breast feeding women may need supplementation as well.

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Recommended Dietary Allowance (RDA) for vitamin C:

 

For nonsmoking, nonpregnant women, have 75 mg daily. For nonsmoking men,  90 mg daily.  Smokers need to consume additional 35 mg per day. 

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Examples for servings providng the minimal vitamin C daily needs are 1 kiwifruit, 1-2 oranges, 1 cup of strawberries, 1 pepper or1 cup of broccoli (raw or cooked), 6 raw tomatos, 8 Brussels sprouts (cooked).

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