Vitamin C, also known as ascorbic acid, is an essential water-soluble nutrient and powerful antioxidant. It plays a crucial role in several bodily functions:
Immune FunctionÂ
Vitamin C supports the immune system by stimulating the production and function of white blood cells and acting as an antioxidant.
Collagen Synthesis
Vitamin C is vital for collagen synthesis, healthy skin, wound healing, and maintaining the integrity of connective tissues.
Antioxidant Function
As an antioxidant, vitamin C helps combat free radicals in the body, reducing oxidative stress and potentially lowering the risk of chronic diseases.
Iron AbsorptionÂ
Vitamin C enhances the absorption of non-heme iron, the form of iron found in plant-based foods, which is critical for preventing anemia among vegetarians.
The recommended daily intake of vitamin C is 90mg for men and 75 mg per day for women. However, for women, the need increases to 85 mg during pregnancy and 120 mg while breastfeeding.
While vitamin C is generally safe, excessive intake (usually from supplements, not food) can lead to adverse effects like diarrhea, nausea, and stomach cramps. The upper limit for adults is 2,000 mg per day. Taking too much over a prolonged period can lead to more health issues.
Vitamin C intake depends on age, sex, and specific health conditions. Adhering to the recommended dietary allowances through a balanced diet or standard supplements is sufficient and safe.
Before we get into the genetics of vitamin C status, it is essential to understand how the body absorbs it.Â
Vitamin C absorption in the body primarily occurs in the small intestine through a mechanism involving sodium-dependent vitamin C transporters (SVCT1 and SVCT2). SVCT1, located in the small intestine, is responsible for the uptake of vitamin C from dietary sources. Once absorbed, vitamin C moves via the bloodstream to various tissues, where SVCT2 aids cell uptake.
The body regulates vitamin C absorption, and its efficiency can decrease as intake increases, meaning that very high doses are not effectively absorbed. Excess vitamin C gets excreted in the urine.
The SLC23A1 gene encodes the SVCT1 protein. Predominantly located in the epithelial cells of the small intestine and kidneys, SVCT1 plays a vital role in absorbing vitamin C from dietary sources and reabsorbing it from the kidneys, thus regulating its levels in the body.
In 2010, a two-stage study evaluated the connection between genetic variations in the SLC23A1 gene and the levels of l-ascorbic acid (vitamin C) in the bloodstream. The first stage used the British Women’s Heart and Health Study as the discovery cohort, followed by a series of follow-up cohorts. The second stage was a meta-analysis that included a total of 15,087 participants.Â
The study found that a specific genetic variant, rs33972313 (C/T), located in the SLC23A1 gene (which encodes a vitamin C transporter), is associated with lower levels of l-ascorbic acid in the blood. Each additional copy of the minor allele (T) was linked to a decrease in l-ascorbic acid levels by approximately 5.98 μmol/L.
The significance of the rs33972313 variant in plasma vitamin C levels was further confirmed in a 2021 GWAS.
The SLC23A2 gene encodes the SVCT2 protein. This transporter is expressed in almost all body tissues, particularly in areas with high metabolic activity, like the brain, eyes, and adrenal glands. SVCT2 ensures the delivery of vitamin C to these essential tissues, supporting its role in antioxidant protection and enzyme function.
In a 2011 case-control study conducted in the Mediterranean population, researchers identified a significant association between the rs1279386 (A>G) SNP in the SLC23A2 gene and the risk of primary open-angle glaucoma (POAG).
In their analysis, individuals homozygous for the G allele (GG) showed a higher risk of developing POAG when compared to other genotypes. Additionally, the study found that POAG patients generally had lower plasma vitamin C levels than control subjects.
In a 2021 GWAS, the researchers found a significant genetic association involving the SLC23A3 gene on chromosome 2. This gene encodes the sodium-dependent vitamin C transporter 3 (SVCT3), which is part of the same transporter family as SLC23A1. The SNP rs13028225 displayed a strong association with plasma vitamin C levels.
SVCT3 has a largely unknown functional role. However, existing evidence indicates that SVCT3 is primarily expressed in the kidneys. It suggests that genetic variations in SLC23A3 could influence circulating vitamin C levels by impacting renal function and consequently affecting vitamin C reabsorption in the kidneys.
The study also uncovered other candidate SNPs affecting vitamin C levels:
Diet: We get vitamin C from fruits and vegetables, with some of the richest sources being citrus fruits, berries, kiwi, bell peppers, and dark green leafy vegetables like kale and spinach. Notably, the vitamin C content in food can be reduced by prolonged storage and cooking, as vitamin C is water-soluble and sensitive to heat. Eating fresh and minimally cooked fruits and vegetables maximizes vitamin C intake.
Age and Gender: Vitamin C requirements vary across different ages and genders. For instance, infants have lower needs, while pregnant and breastfeeding women require higher amounts. Men generally require slightly more vitamin C than women. As people age, their ability to absorb vitamin C can decrease, potentially increasing their need for this nutrient.
Lifestyle Habits: Smoking significantly increases oxidative stress and metabolic demand for antioxidants. Hence, smokers require more vitamin C than non-smokers. Similarly, excessive alcohol consumption can impair the body’s ability to absorb and store vitamin C. It leads to reduced vitamin C levels.
Health Conditions: Certain illnesses, particularly those causing inflammation or fever, can increase the body’s need for vitamin C. Stress, both physical and emotional, elevates cortisol levels, which can deplete vitamin C stores. Chronic conditions, like diabetes and heart disease, may also increase the demand for vitamin C due to heightened oxidative stress.
Medications: Some medications, including certain types of birth control and aspirin, can lower vitamin C levels in the body. Diuretics, used for high blood pressure, increase the excretion of vitamin C, potentially leading to lower levels.
Environmental Factors: Exposure to pollutants and toxins, such as cigarette smoke (even second-hand) and heavy metals, can increase oxidative stress in the body, thereby increasing the need for vitamin C. Urban environments with higher pollution levels might contribute to a greater demand for antioxidants, including vitamin C, compared to less polluted areas.
To improve vitamin C levels, consider these recommendations:
*Understanding your genetics can offer valuable insights into your well-being, but it is not deterministic. Your traits can be influenced by the complex interplay involving nature, lifestyle, family history, and others.
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