Fat-soluble vitamins A, D, E and K: Their functions, main sources and recommended doses

Fat-soluble vitamins

Most of the vitamins that a person needs are dissolved in water. But there are four fat-soluble vitamins: they are much better absorbed into the bloodstream, if you eat them with fat: These are vitamins  A,   D , E, and  the K. I will tell you what their health benefits are and what are the main sources.

Vitamin A

This vitamin supports many functions of the body:

– Sight (necessary for photosensitive eye cells and for the formation of a tear fluid);

– Immune function;

– Cell growth;

– Growth of hair ( deficiency leads to hair loss);

– Reproductive function and significance for fetal development.

Food Sources

Vitamin A is found only in animal sources of food, mainly in the liver, fish oil and butter. Provitamin A can be obtained from carotenoids – antioxidants contained in plants. Beta-carotene is the most effective, it is abundant in carrots, kayle, spinach, red, yellow and orange vegetables, as well as some dark green leafy vegetables.

Consumption rate

The recommended daily dose of vitamin A is 900 μg for men and 700 μg for women. For infants up to a year, 400-500 mcg, for children from 1 to 3 years – 300 mcg, from 4 to 8 years – 400 mcg, from 9 to 13 years – 600 mcg.

Vitamin A deficiency

Vitamin A deficiency is rare in developed countries. However, it can be experienced by vegans, since vitamin A in ready-for-consumption form is found only in animal sources of food. Although provitamin A is found in fruits and vegetables, it is not always effectively transformed into retinol, the active form of vitamin A (efficacy depends on human genetics).

A shortage of this vitamin can cause a diet based on refined rice and potatoes, with a lack of fat and vegetables.

A sign of an early deficit is  night blindness (poor twilight vision). Consequences of deficiency: dry eye syndrome, blindness, hair loss, skin problems (hyperkeratosis, or goosebumps); suppression of the immune function.


Hypervitaminosis A is a rare phenomenon, but with serious consequences. The main reasons are excessive consumption of vitamin A from food additives, liver or fish oil. But the consumption of provitamin A does not cause hypervitaminosis.

The main symptoms: fatigue, headaches, irritability, abdominal pain, joint pain, lack of appetite, vomiting, blurred vision, skin problems and inflammation in the mouth and eyes, liver damage, bone loss, hair loss.

The upper limit of consumption is 900 mcg per day for adults.

Fat-soluble vitamins
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Vitamin D

Two functions of vitamin D are well studied (and in fact there are many more):

– Maintenance of bone tissue: vitamin D helps to assimilate calcium and phosphorus from the diet and regulates the levels of these most important minerals for bones;

– Strengthening the immune system.


Vitamin D, or calciferol – is a collective term for several fat-soluble compounds. It exists in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).

After absorption into the blood, the liver and kidneys convert calciferol to calcitriol, a biologically active form of vitamin D. It can also be deposited in the body for later use in the form of calcidiol.

Sources of vitamin D

The body produces the right amount of vitamin D3, if a significant part of the skin regularly gets sun rays . But many people spend little time in the sun or fully dressed even in sunny, hot time. A sunscreen, although it is recommended to use it all, reduces the amount of vitamin D produced by the skin. For example, for several years I have lived exclusively in hot sunny countries and yet experienced a shortage of vitamin D.

As a result, you need to replenish vitamin D from the diet.

Few foods naturally contain vitamin D. The best food sources are fatty fish, fish oil and eggs (vitamin B3). Mushrooms that have been exposed to ultraviolet light can also contain vitamin D2.

Consumption rate

For children and adults, the daily norm of vitamin D is 15 μg, for the elderly it is 20 μg.

Vitamin D deficiency

Severe vitamin D deficiency is rare.

Risk factors for “soft forms” of deficiency: dark skin color, elderly age, obesity, lack of exposure to sunlight and diseases that interfere with fat absorption.

The consequences of vitamin D deficiency: a decrease in bone density, weak muscles, an increased risk of fractures, weak immunity. Among the signs are also fatigue, depression, hair loss and slow healing of wounds.

Overdose of vitamin D

Toxicity is very rare. Long stay in the sun does not cause hypervitaminosis, but a large number of supplements can lead to hypercalcemia – an excessive amount of calcium in the blood.

Symptoms: headache, nausea, loss of appetite and weight, fatigue, damage to the kidneys and heart, high blood pressure, fetal abnormalities in pregnant women. The upper limit of daily intake for adults is 100 μg.

You may also like to read: More means less vitamin D cancer

Vitamin E

Being a powerful antioxidant, vitamin E protects cells from premature aging and damage by free radicals. Antioxidant properties are enhanced by vitamins C, B3 and selenium. In large quantities, vitamin E dilutes the blood (reduces its coagulability).


Vitamin E is a family of eight antioxidants: tocopherols and tocotrinols. Alpha-tocopherol – the most common form of vitamin E, is about 90% of this vitamin in the blood.

Sources of information

The most powerful sources of vitamin E are some vegetable oils, seeds and nuts, avocados, peanut butter, fatty fish and fish oils.

Consumption rate

For adults, the recommended daily dose of vitamin E is 15 mg, for children and adolescents the dosage varies: 6-7 mg for children 1-8 years, 11 mg for children 9-13 years, 15 mg for children 14-18 years.

Vitamin E deficiency

Deficiency is rare, usually with diseases that prevent the absorption of fat or vitamin E from food (cystic fibrosis, liver disease).

Symptoms of vitamin E deficiency: muscle weakness, difficulty with movement, tremor, vision problems, weak immune function, numbness.

Long-term deficiency can lead to anemia, heart disease, severe neurological problems, blindness, dementia, reflex reflexes and inability to fully control body movements.

Overdose of vitamin E

Overdose is unlikely, it occurs only because of the large number of supplements. Possible consequences – blood thinning, a decrease in the effectiveness of vitamin K and heavy bleeding. People taking blood thinning medications should avoid large doses of vitamin E.

Vitamin K

Vitamin K plays a key role in the process of blood clotting. Without it, you risk dying from bleeding. He also supports bone health and helps prevent calcification of blood vessels, reducing the risk of cardiovascular disease.


Vitamin K – compounds, divided into two main groups. Vitamin K1 (phylloquinone) is the main form of vitamin K in the diet, and vitamin K2 (menaquinone).

Food Sources

Vitamin K1 is found in plant food sources (primarily green leafy vegetables). And vitamin K2 is found in small amounts in fatty foods of animal origin (egg yolk, butter, liver) and in fermented soy products. It is also produced by intestinal bacteria in the large intestine.

The intake of vitamin K

Adequate intake of vitamin K – 90 mcg for women and 120 mcg for men. For children, the value ranges from 30 to 75 mcg, depending on the age.

Deficiency of vitamin K

Unlike vitamins A and D, vitamin K does not accumulate in the body. The lack of vitamin K in the diet leads to its deficit in just a week.

In the risk zone, first of all, people whose body is not able to effectively absorb fats (due to celiac disease, inflammatory bowel disease, cystic fibrosis).

To increase the risk of deficiency, antibiotics of a wide spectrum of action and very high doses of vitamin A, which reduces the absorption of vitamin K.

Excess doses of vitamin E can counteract the effects of vitamin K on blood coagulability. Without vitamin K, blood will not curdle, and even a small wound can lead to insuperable bleeding.

A low level of vitamin K is also associated with a decrease in bone density and the risk of fractures in women.

Overdose of vitamin K

Natural forms of vitamin K are not toxic.

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