It is a truth sheet meant for well being professionals. For a reader-friendly overview of Vitamin C, see our client truth sheet on Vitamin C.
For info on Vitamin C and COVID-19, see the NIH COVID-19 Remedy Tips on Vitamin C.
COVID-19
Introduction
Vitamin C, also called L-ascorbic acid, is a water-soluble vitamin that’s naturally current in some meals, added to others, and accessible as a dietary complement. People, not like most animals, are unable to synthesize vitamin C endogenously, so it’s a necessary dietary element [1].
Vitamin C is required for the biosynthesis of collagen, L-carnitine, and sure neurotransmitters; vitamin C can also be concerned in protein metabolism [1,2]. Collagen is a vital part of connective tissue, which performs a significant function in wound therapeutic. Vitamin C can also be an necessary physiological antioxidant [3] and has been proven to regenerate different antioxidants inside the physique, together with alpha-tocopherol (vitamin E) [4]. Ongoing analysis is analyzing whether or not vitamin C, by limiting the damaging results of free radicals by way of its antioxidant exercise, may assist forestall or delay the event of sure cancers, heart problems, and different ailments during which oxidative stress performs a causal function. Along with its biosynthetic and antioxidant capabilities, vitamin C performs an necessary function in immune operate [4] and improves the absorption of nonheme iron [5], the type of iron current in plant-based meals. Inadequate vitamin C consumption causes scurvy, which is characterised by fatigue or lassitude, widespread connective tissue weak point, and capillary fragility [1,2,4,6-9].
The intestinal absorption of vitamin C is regulated by a minimum of one particular dose-dependent, energetic transporter [4]. Cells accumulate vitamin C through a second particular transport protein. In vitro research have discovered that oxidized vitamin C, or dehydroascorbic acid, enters cells through some facilitated glucose transporters and is then decreased internally to ascorbic acid. The physiologic significance of dehydroascorbic acid uptake and its contribution to total vitamin C financial system is unknown.
Oral vitamin C produces tissue and plasma concentrations that the physique tightly controls. Roughly 70%–90% of vitamin C is absorbed at average intakes of 30–180 mg/day. Nevertheless, at doses above 1 g/day, absorption falls to lower than 50% and absorbed, unmetabolized ascorbic acid is excreted within the urine [4]. Outcomes from pharmacokinetic research point out that oral doses of 1.25 g/day ascorbic acid produce imply peak plasma vitamin C concentrations of 135 micromol/L, that are about two instances increased than these produced by consuming 200–300 mg/day ascorbic acid from vitamin C-rich meals [10]. Pharmacokinetic modeling predicts that even doses as excessive as 3 g ascorbic acid taken each 4 hours would produce peak plasma concentrations of solely 220 micromol/L [10].
The overall physique content material of vitamin C ranges from 300 mg (at close to scurvy) to about 2 g [4]. Excessive ranges of vitamin C (millimolar concentrations) are maintained in cells and tissues, and are highest in leukocytes (white blood cells), eyes, adrenal glands, pituitary gland, and mind. Comparatively low ranges of vitamin C (micromolar concentrations) are present in extracellular fluids, akin to plasma, pink blood cells, and saliva [4].
Beneficial Intakes
Consumption suggestions for vitamin C and different vitamins are offered within the Dietary Reference Intakes (DRIs) developed by the Meals and Diet Board (FNB) on the Institute of Drugs (IOM) of the Nationwide Academies (previously Nationwide Academy of Sciences) [8]. DRI is the overall time period for a set of reference values used for planning and assessing nutrient intakes of wholesome individuals. These values, which differ by age and gender [8], embrace:
Desk 1 lists the present RDAs for vitamin C [8]. The RDAs for vitamin C are primarily based on its identified physiological and antioxidant capabilities in white blood cells and are a lot increased than the quantity required for defense from deficiency [4,8,11]. For infants from beginning to 12 months, the FNB established an AI for vitamin C that’s equal to the imply consumption of vitamin C in wholesome, breastfed infants.
* Satisfactory Consumption (AI)
Sources of Vitamin C – “is vitamin c water soluble”
Meals
Fruit and veggies are the perfect sources of vitamin C (see Desk 2) [12]. Citrus fruits, tomatoes and tomato juice, and potatoes are main contributors of vitamin C to the American eating regimen [8]. Different good meals sources embrace pink and inexperienced peppers, kiwifruit, broccoli, strawberries, Brussels sprouts, and cantaloupe (see Desk 2) [8,12]. Though vitamin C shouldn’t be naturally current in grains, it’s added to some fortified breakfast cereals. The vitamin C content material of meals could also be decreased by extended storage and by cooking as a result of ascorbic acid is water soluble and is destroyed by warmth [6,8]. Steaming or microwaving could reduce cooking losses. Happily, most of the finest meals sources of vitamin C, akin to vegatables and fruits, are normally consumed uncooked. Consuming 5 various servings of vegatables and fruits a day can present greater than 200 mg of vitamin C.
*DV = Each day Worth. The U.S. Meals and Drug Administration (FDA) developed DVs to assist shoppers evaluate the nutrient contents of meals and dietary dietary supplements inside the context of a complete eating regimen. The DV for vitamin C is 90 mg for adults and youngsters age 4 years and older [13]. FDA doesn’t require meals labels to record vitamin C content material until vitamin C has been added to the meals. Meals offering 20% or extra of the DV are thought-about to be excessive sources of a nutrient, however meals offering decrease percentages of the DV additionally contribute to a healthful eating regimen.
The U.S. Division of Agriculture’s (USDA’s) FoodData Central lists the nutrient content material of many meals and offers a complete record of meals containing vitamin C organized by nutrient content material and by meals identify.
Dietary dietary supplements
Dietary supplements usually comprise vitamin C within the type of ascorbic acid, which has equal bioavailability to that of naturally occurring ascorbic acid in meals, akin to orange juice and broccoli [14-16]. Different types of vitamin C dietary supplements embrace sodium ascorbate; calcium ascorbate; different mineral ascorbates; ascorbic acid with bioflavonoids; and mixture merchandise, akin to Ester-C®, which accommodates calcium ascorbate, dehydroascorbate, calcium threonate, xylonate and lyxonate [17].
A couple of research in people have examined whether or not bioavailability differs among the many varied types of vitamin C. In a single examine, Ester-C® and ascorbic acid produced the identical vitamin C plasma concentrations, however Ester-C® produced considerably increased vitamin C concentrations in leukocytes 24 hours after ingestion [18]. One other examine discovered no variations in plasma vitamin C ranges or urinary excretion of vitamin C amongst three completely different vitamin C sources: ascorbic acid, Ester-C®, and ascorbic acid with bioflavonoids [17]. These findings, coupled with the comparatively low value of ascorbic acid, led the authors to conclude that easy ascorbic acid is the popular supply of supplemental vitamin C [17].
Vitamin C Intakes and Standing
In response to the 2001–2002 Nationwide Well being and Diet Examination Survey (NHANES), imply intakes of vitamin C are 105.2 mg/day for grownup males and 83.6 mg/day for grownup females, assembly the at present established RDA for many nonsmoking adults [19]. Imply intakes for youngsters and adolescents aged 1-18 years vary from 75.6 mg/day to 100 mg/day, additionally assembly the RDA for these age teams [19]. Though the 2001–2002 NHANES evaluation didn’t embrace information for breastfed infants and toddlers, breastmilk is taken into account an sufficient supply of vitamin C [8,14]. Use of vitamin C-containing dietary supplements can also be comparatively frequent, including to the full vitamin C consumption from meals and drinks. NHANES information from 1999–2000 point out that roughly 35% of adults take multivitamin dietary supplements (which usually comprise vitamin C) and 12% take a separate vitamin C complement [20]. In response to 1999–2002 NHANES information, roughly 29% of youngsters take some type of dietary complement that accommodates vitamin C [21].
Vitamin C standing is usually assessed by measuring plasma vitamin C ranges [4,14]. Different measures, akin to leukocyte vitamin C focus, may very well be extra correct indicators of tissue vitamin C ranges, however they’re tougher to evaluate and the outcomes aren’t at all times dependable [4,9,14].
Vitamin C Deficiency
Acute vitamin C deficiency results in scurvy [7,8,11]. The timeline for the event of scurvy varies, relying on vitamin C physique shops, however indicators can seem inside 1 month of little or no vitamin C consumption (beneath 10 mg/day) [6,7,22,23]. Preliminary signs can embrace fatigue (most likely the results of impaired carnitine biosynthesis), malaise, and irritation of the gums [4,11]. As vitamin C deficiency progresses, collagen synthesis turns into impaired and connective tissues grow to be weakened, inflicting petechiae, ecchymoses, purpura, joint ache, poor wound therapeutic, hyperkeratosis, and corkscrew hairs [1,2,4,6-8]. Extra indicators of scurvy embrace despair in addition to swollen, bleeding gums and loosening or lack of tooth resulting from tissue and capillary fragility [6,8,9]. Iron deficiency anemia may also happen resulting from elevated bleeding and decreased nonheme iron absorption secondary to low vitamin C consumption [6,11]. In kids, bone illness could be current [6]. Left untreated, scurvy is deadly [6,9].
Till the tip of the 18th century, many sailors who ventured on lengthy ocean voyages, with little or no vitamin C consumption, contracted or died from scurvy. In the course of the mid-1700s, Sir James Lind, a British Navy surgeon, performed experiments and decided that consuming citrus fruits or juices may remedy scurvy, though scientists didn’t show that ascorbic acid was the energetic element till 1932 [24-26].
In the present day, vitamin C deficiency and scurvy are uncommon in developed international locations [8]. Overt deficiency signs happen provided that vitamin C consumption falls beneath roughly 10 mg/day for a lot of weeks [5-8,22,23]. Vitamin C deficiency is rare in developed international locations however can nonetheless happen in individuals with restricted meals selection.