Fat-soluble vitamins
Vitamin A (retinolis) and Carotenoids
Vitamin A consists of biologically active retinol compounds and its precursors, carotenoids. Carotenoids include zeaxanthin, the pigment of sweet corn, and lycopene, the red color pigment of tomatoes.
Retinal is important for maintaining good vision and preventing night blindness. In the presence of light stimuli, chemical breakdown of rhodopsin from proteins occurs, and new rhodopsin molecules are produced with the help of vitamin A. A deficiency in vitamin A can lead to worsened vision, dryness of the cornea, deterioration of the conjunctiva, disappearance of the protective tear film, and the development of corneal erosions. This is relevant for individuals who work on computers.
In the absence of vitamin A, the skin epithelium thickens, the channels of subcutaneous sebaceous glands become clogged, leading to follicular inflammation. The body’s resistance decreases, making individuals more susceptible to intestinal and respiratory tract infections. Fats are necessary for the absorption of vitamin A. Retinol is obtained from animal-derived food products, even in small amounts of fat. Overdosing on supplements can lead to chronic toxic effects, manifested by headaches, muscle and bone pain, ataxia, skin damage, alopecia, liver dysfunction, and hyperlipidemia. Not all symptoms are reversible. Vitamin A is teratogenic, and the amount consumed during pregnancy should not exceed the RDA. The amounts of carotenoids in food products are not toxic, but the skin may acquire a yellowish hue. It is not recommended to eat liver or pâté during pregnancy.
The recommended daily allowance (RDA) is 800 μg/d retinol equivalents, 1000 μg/d for pregnant women, and 1200 μg/d for lactating women.
Food Sources of Vitamin A
Retinol: beef liver, pâté, fatty fish and fish liver oil, egg yolks, milk, cream, cheeses.
Carotenes: carrots, pumpkins, red bell peppers, spinach, tomatoes.
Vitamin E
Vitamin E is a potent antioxidant that protects cells from the formation of free radicals, maintains the integrity of cell membranes, regulates prostaglandin production, and participates in DNA synthesis.
A deficiency of vitamin E is rarely observed in healthy individuals. In cases of malabsorption, cystic fibrosis, and cholestatic liver diseases, the following symptoms may occur: nervous system, digestive system, and reproductive disorders. The levels of vitamin E depend on the amount of polyunsaturated fatty acids (PUFAs): 0.4 mg of α-tocopherol is present in one gram of PUFAs consumed with food.
Vitamin E is minimally toxic, but in very high doses, it acts as an antagonist to vitamins A, D, and K. Symptoms of toxic effects include headaches, nausea, muscle weakness, blurred vision, creatinuria, and gastrointestinal disturbances.
Food Sources of Vitamin E
Wheat germ oil, almonds, sunflower seeds, their oil, hazelnuts, peanuts, their butter, corn oil.
The recommended daily allowance (RDA) is 10 mg of tocopherol equivalents per day.
Vitamin D (calciferol)
The term vitamin D encompasses two chemical compounds – ergocalciferol (D2) and cholecalciferol (D3). Vitamin D and its metabolites actively participate in the process of bone mineralization, maintain the balance of the immune system, and inhibit the proliferation of certain cancer cell types.
Vitamin D is best obtained in the summer. In winter, in the absence of sunlight and a deficiency of vitamin D in food, adults may develop osteomalacia, characterized by bone pain, muscle weakness, and decreased resistance to infections. Malabsorption caused by various diseases, avoidance of animal products, increases the risk of vitamin D deficiency.
Exceeding the daily allowance can lead to increased cholesterol levels, the development of atherosclerosis, hypercalcemia, and kidney stones.
The recommended daily allowance (RDA) is 5 μg/d.
Food Sources of Vitamin D
Cod liver, fatty marine fish, milk, margarine, eggs, liver.
Vitamin K (phylloquinone)
Vitamin K is found in plants. This vitamin is synthesized by intestinal bacteria.
Vitamin K is involved in the production of key clotting factors (II, VII, IX, and X). Together with vitamin D, it participates in bone regeneration, reducing the risk of osteoporosis. A deficiency in vitamin K is characterized by poor blood clotting and low prothrombin activity. Vitamin K deficiency in adults is rare but can occur in individuals with obstructive jaundice, antibiotic therapy, or when taking anticoagulants.
The recommended daily allowance isnorm (RPN) – 0.2–0.3 mg/day.
Sources of Vitamin K
Dark leafy vegetables (spinach, broccoli, leafy greens), oils, especially soybean oil, eggs, meat, dairy products.
Source | Dietary Treatment in General Practice | Dietitian Doctor Jūratė Dobrovolskienė