Which ones are they
Antioxidant vitamins are three types of molecules that are quite heterogeneous, both in terms of their chemical-physical characteristics and in terms of the food sources that contain them.
- Vitamin A and β- carotene
- C vitamin
- Vitamin E
Water-soluble antioxidant vitamins
C vitamin
The only water-soluble antioxidant vitamin is vitamin C or L-ascorbic acid . This vitamin has the ability to oxidize into dehydroascorbic acid and reversibly reduce; it intervenes in numerous functions of hydroxylation, favors the reduction of folic acid and promotes the absorption of iron by reduction of Fe 3+ to Fe 2+ .
As far as its antioxidant activity is concerned, vitamin C participates in the cellular defense processes FIGHTING THE FREE RADICALS of oxygen by donating an electron to the tocopheryl-radical; in this way, vitamin C restores the anti-radical activity of another antioxidant vitamin: vitamin E or tocopherol .
Almost all of the vitamin C taken with food is absorbed, while at high doses almost 85% remains in the faeces . Vitamin C deficiency
was a typical sign of sailors who, lacking fresh fruit and vegetables to consume on long sea voyages, developed scurvy . Today, fortunately, the lack of vitamin C no longer reaches similar levels even if it is not uncommon for the diet to be somewhat deficient (especially in the elderly population – about 9% of the elderly ) ; excess vitamin C is not healthy but doses up to 10g/day “seem” safe.
Vitamin C is contained in foods of vegetable origin ( citrus fruits , kiwis , peppers , tomatoes and green leafy vegetables ) FRESH; on the contrary, the loss of vitamin C is proportional to the storage time, washing (by dilution), cooking , light and oxidation.
The recommended ration of vit. C for adults should not be <10mg and should instead range between 45-60mg/day; smokers have a greater need (about +30mg), as well as pregnant women (+10mg) and nurses ( +30mg).
Fat-soluble antioxidant vitamins
Vitamin A and β-carotene
Vitamin A or retinol and β-carotene have the same vitamin functions , even if six units of β-carotene correspond to each unit of retinol (and many more for the other 500-600 carotenoid species ). Retinol, present in animal foods, is stored in large quantities in the liver which (if needed) releases it into the circulation (quantities < 20mg/dl in the blood indicate imminent depletion of stocks); on the contrary, carotenoids are pigments found mainly in vegetables and fruit .
Vitamin A is essential for cellular differentiation (also of the immune system ), but the real antioxidant function is better attributable to carotenoids which (although having poor vitamin A function) by themselves neutralize singlet oxygen (a powerful PROoxidant).
Vitamin A and β-carotene deficiency is closely related to vision disorders (twilight blindness) and high incidence of tumors due to oxidative stress ; toxicity occurs with doses of 300mg /day.
The recommended rations range from 350 retinol equivalents (RE) in children to 900 RE in nurses.
NB. RE = 1 mg of retinol = 6 mg of β-carotene = 12 mg of other active carotenoids.
Vitamin E
Vitamin E includes several forms of tocopherols: α , β, γ and δ tocopherol, although the most active is α-tocopherol; vitamin E is absorbed in the small intestine, also thanks to the action of bile acids, up to 20-40% of the total ingested. In the blood, vitamin E moves bound to transport lipoproteins and the richest deposits in the body are made up of adipose tissue .
The antioxidant action of vitamin E consists in blocking the degeneration of polyunsaturated fatty acids ( PUFA ), including the essential ones ( AGE ), activated by peroxylipid free radicals ; this SHIELDING action represents one of the major defenses that the organism possesses against the stress of the AGEs contained in the phospholipids of the cell membrane (for the same reason, tocopherols are frequently used as an antioxidant additive in vegetable oils rich in PUFA fatty acids ).
Vitamin E deficiency is almost unknown and does not occur in normal individuals, while pharmacological excess (>2000mg/day) can only be attributed to intestinal disorders .
Vitamin E is contained in lipids of vegetable origin; seeds and all dried fruit , some cereals , wheat germ , fresh fruit and vegetables , soy and peanuts are rich in it . Unfortunately, despite its diffusion, vitamin E is also very sensitive ; damage it: light, heat, alkaloids , iron and copper . For this reason it would be advisable to introduce at least 0.4 mg of tocopherol equivalents (TE) in the diet for every gram of PUFA taken in the diet; e.g. on a 2000kcal diet and relative 5.5-5.6g of PUFA, approximately 2.2-2.3mg/day of vitamin E would be needed.
ACE Against Heart Attack
Scientific research has by now amply demonstrated that the lack of vitamins A -CE (and to tell the truth also of selenium ) favors the onset of unfortunate events affecting the cardio -circulatory system. However, if it is true that the lack of antioxidants predisposes to ischemic heart disease , it is equally true that a diet rich in ACE vitamins is protective against myocardial infarction and atherogenesis in general.
Analyzing the importance of antioxidants in the diet, it emerged that there is an inverse relationship between plasma levels of antioxidant vitamins and MORTALITY due to ischemic heart disease , as well as an inverse relationship between the consumption of FRESH fruit and VEGETABLES rich in antioxidant vitamins and cardiovascular MORTALITY; moreover, a correlation between low levels of vitamin E and the presence of angina pectoris ( heart pain ) is also suspected.
This simply translates into a PROTECTIVE function of antioxidant vitamins (and in particular of vitamin E) on atherosclerotic pathologies .
It’s not all! Tocopherols also seem to hinder the oxidation of transport lipoproteins, preserving their integrity and efficiency, and therefore also their natural uptake by hepatic and peripheral receptors , preventing their interstitial deposition as a trigger of atherogenesis.
Attention! Vitamin E supplementation may be contraindicated in patients on anticoagulant treatment .
Bibliography
- Post-infarction and associated pathologies. Preventive and curative interventions and associated pathologies. Volume II – A. Zangara – Piccin – page 431:433.
