Hladiny a koncentrace vitamínu C
Bez vit. C
Interval bez nutnosti dodávat vit. C když je tělo saturované
- Cca 2 months
- Appearance of clinical signs
- Alespoň 6.5-10 mg/day vitamin C to prevent scurvy
- vitamin C status will reflect the regularity of fruit and vegetable consumption
- Socio-economic conditions
- From one month to more than six months
- Depending on previous loading of vitamin C [12]
Plazmatické hladiny a deficit
Vitamín C deficiency a hladiny
- Plasma concentration below 23 µM [3]
- Affects around 10% of adults [3]
- 10%–20% of the western population can be diagnosed with VitC deficiency [3]
- During depletion vitamin C is lost
- Cca 3 % of whole body content per day [4]
Clinical signs of scurvy appear
- In men at intakes lower than 10 mg/day [4]
- When the whole body content falls below 300 mg [4]
- Associated with plasma ascorbate concentrations below 11 mmol/l
- Associated with leukocyte vit. C levels less than 2 nmol/108 cells [4]
- Plasma concentrations fall to around 11 mmol/l
- When dietary vitamin C is between 10 and 20 mg/day [4]
Terapie deficience vitamínu C a hladiny
- vitamin C required to prevent or cure early signs of deficiency
- 6.5 - 10 mg/day
- Represents the lowest physiologic requirement [4]
- Intakes greater than 25-35 mg/day
- Plasma concentrations start to rise steeply
- Indicating a greater availability of vitamin C for metabolic needs [4]
Suplementace vitamínu C a hladiny
- Supplementací vit. C dojde i ke zvýšení koncentrací v tkáních oka
- Nejednoznačné výsledky studií asociace katarakty a hladin vit. C
- Studie EPIC
- Téměř 20 tisíc osob
- Nárůst sérové koncentrace askorbátu o 20 µmol
- Snižuje mortalitu o 20 % [1]
Plasmatické hladiny a normy
- Plazmatické norm. 8-14 mg/l
Biologický poločas v plazmě
- Askorbátu v plazmě po i.v. 7,5 g u zdravých cca 1,5 h [2]
Hladiny a obsahy vit. C v různých tkáních
- Is more stable
- Can give a better view of the availability of ascorbate within the entire organism
- Very few hospital laboratories are adequately equipped and trained to carry out such detailed analyses [12]
Saturace tkání vitamínem C a hladiny v plazmě
- Při saturaci plazmy askorbátem se hladina ustaluje
- Fyziologická hodnota kolem 0,08 mmol [1]
- St.p. i.v. plazmatické hladiny
- > 2,38 mmol po infuzi 7,5 g kyseliny askorbové
- At tissue saturation, whole body vitamin C content
- Cca 20 mg/kg
- Or 1500 mg [4]
- Plasma ascorbate closely reflects the dietary intake
- Ranges between 20 and 80 mmol/l [4]
- National Instit of Health
Tkáně s vyšší konc. vit. C než jsou v plazmě
- V čočce cca 10X vyšší hl. než v plazmě
- V sítnici cca 100X vyšší než v plazmě
- Sklivec cca 20X vyšší koncentrace než v plazmě
- žaludeční sliznice vyšší konc.
- Vyšší hladiny vit. C v CNS
Adrenal glands
- 550 mg/kg [11]
- SVCT2 is the main transporter in the adrenal glands
- Maintains high concentrations of ascorbate in the chromaffin cells of the adrenal medulla
- Essential for the synthesis of catecholamines [11]
Brain
- 140 mg/kg [11]
- ascorbate located in the cerebrospinal fluid
- Diffuses freely into the extracellular space of neurons and glia
- Captured by both cell types via SVCT2 (except for astrocytes) [11]
Pituitary and adrenal glands
- Can exceed 2,000 µmol/L [12]
Liver
- 125 mg/kg [11]
- SVCT1 is the most abundant transporter in the liver
- Decrease in the ascorbate uptake in rat hepatocytes due to a lower expression of the mRNA of SVCT1 associated with age [11]
- SVCT2 is also expressed
Skeletal muscle
- Concentration of 35 mg/kg [11]
- 200-300 µmol/L [12]
In the urine
- Reflect recent dietary intake rather than total body content
- Serum or blood plasma concentrations
- Follow a circadian rhythm
- Reflect short-term dietary impact [12]
