Vitamins are substances that are essential for the body to function properly and should be provided with the diet. They are divided into two main groups:

• water-soluble vitamins,
• fat-soluble vitamins.

The vitamin A, D, E and K complex is a group of fat-soluble compounds. These nutrients are characterised by the fact that they are stored in the body - unlike water-soluble vitamins, which are easily excreted from the body in the urine - and are responsible for maintaining the harmonious operation of many systems in the body. Each vitamin has specific properties to take care of, among other things, immunity and the condition of the skin and bones ^[1].

Vitamin A - not just beautiful skin

With a proper diet, it is possible to provide the body with vitamin A in two forms:

• preformed vitamin A (which includes retinol and retinyl esters) - its source is animal products;
• provitamin A carotenoids (which are mainly beta-carotene, alpha-carotene, beta-cryptoxanthin) - substances of plant origin, which are converted to vitamin A in the intestine ^[2].

The main properties of vitamin A include playing a role in cell specialisation and helping to maintain healthy skin. Studies have shown that beta-carotene-containing microalgae extracts can help reduce oxidative stress ^[3], as well as support the skin's primary protection against UV radiation to maintain healthy and youthful-looking skin ^{[4, 5, 6]}. As you can see, it is worth stocking up not only on sunscreen for the summer season, but also to take care of the skin from within by taking adequate amounts of beta-carotene. In addition, vitamin A helps to maintain good vision - influencing, among other things, the proper functioning of the conjunctival membranes and cornea ^[2].

Vitamin D - the guardian of immunity

Vitamin D exists in two main forms:

• ergocalciferol (D2),
• cholecalciferol (D3).

Because they differ chemically only in the structure of the side chains, both types are well absorbed in the small intestine ^[7].

Vitamin D (calciferol) - commonly referred to as the sunshine vitamin - differs somewhat from the other fat-soluble compounds in that it is obtained largely from sunlight (exposure to sunlight triggers vitamin D synthesis). Unlike other vitamins, few sources of it can be found in food ^[7]. This vitamin helps in the proper functioning of the immune system, supports the maintenance of healthy bones, teeth and muscles, and regulates the calcium-phosphate balance. It has been shown that adequate levels can reduce the risk of infection ^[8], as well as increase bone mineral density in people of all ages ^[9]. In addition, its intake can contribute to increased muscle strength and improved neuromuscular coordination ^[10].

Vitamin E - youth at your fingertips

Natural vitamin E exists in eight forms, among which are four tocopherols and four tocotrienols. These include:

• alpha- tocopherol,
• beta-tocopherol,
• gamma-tocopherol,
• delta-tocopherol,
• alpha-Tocotrienol,
• beta-Tocotrienol,
• gamma-Tocotrienol,
• delta- tocotrienol.

Alpha- tocopherol (α-Tocopherol,) is the compound that makes up vitamin E and has the highest bioactivity^[11]. Vitamin E belongs to the group of antioxidants - meaning that it protects cells from oxidative stress ^[12]. Antioxidants have the ability to scavenge free radicals so that cell damage does not occur (there must be a balance between free radicals and antioxidants). Vitamin E is a natural source for combating them - it is the main fat-soluble antioxidant that captures superoxide radicals and stops the oxidation of polyunsaturated fatty acids (PUFAs). Studies have shown that vitamin E has immunomodulatory effects, which are beneficial for, among other things, alleviating viral, bacterial and allergic conditions and protecting the body from pathogens ^{[13, 14]}.

Vitamin K - for healthy bones

Vitamin K in food comes in two forms:

• K1 (phylloquinone),
• K2 (menaquinones) - designated MK-4 to MK-13 ^[15].

Studies have shown that MK-7 has the highest bioavailability^[16]. Vitamin K2 helps maintain healthy bones, contributes to normal blood clotting, influences cardiovascular and immune system health, and supports muscle regeneration. It also plays a key role in regulating calcium metabolism. It is an essential nutrient at every stage of life - in both children and adults. It also complements the effects of vitamin D - using these substances together can therefore have beneficial effects on overall health ^[17].

ADEK deficiency - causes, symptoms, how to make up the deficit

Causes of ADEK vitamin deficiency

Reasons for ADEK vitamin deficiency include chronic diseases - especially those with impaired intestinal fat absorption - such a condition can be observed when intestinal inflammation or so-called intestinal permeability occurs ^{[1, 18]}. Insufficient levels of the complex of these vitamins can also be caused by a lack of a balanced diet - based, for example, on low-fat meals. And also obesity, as these vitamins are deposited in adipose tissue.

What are the deficiency symptoms of individual fat-soluble vitamins? What should we eat to ensure an adequate supply?

Symptoms of deficiency and dietary sources of vitamin A

An insufficient supply of vitamin A can manifest as dry eye syndrome (xerophthalmia) and so-called night blindness, with consequent corneal damage and loss of vision. Long-term exposure to a deficiency of this vitamin is also associated with an increased risk of respiratory disorders and anaemia. Studies have also shown that vitamin A intake is effective in controlling acne ^[19].
Provitamin A can be provided by eating, for example, green leafy vegetables (e.g. spinach), orange and yellow vegetables and fruits (e.g. carrots, peppers, pumpkin) and selected vegetable oils ^[2].

Symptoms of deficiency and dietary sources of vitamin D

Vitamin D deficiency is particularly severe for the skeletal system. It can lead to disorders of bone mineralisation, which manifests as skeletal deformities, rickets, dental abnormalities and contractures.
The few dietary sources of vitamin D mainly include fatty fish (e.g. salmon, tuna, mackerel, trout) and fish liver oils. Part of the requirement for this vitamin is also worth supplementing through exposure to sunlight ^[7].

Symptoms of deficiency and dietary sources of vitamin E

A vitamin E deficiency - because it is the main antioxidant - can lead to disorders of the immune system, as well as the occurrence of peripheral neuropathy, ataxia, retinopathy (damage to the retina) and myopathy (muscle weakness).
Alpha-tocopherol, the best-absorbed form of vitamin E, can be found in nuts (e.g. hazelnuts), seeds (e.g. sunflower) and vegetable oils (e.g. sunflower and safflower) ^[11].

Symptoms of deficiency and dietary sources of vitamin K

Vitamin K deficiency can reduce bone mineralisation - increasing the risk of osteoporosis. Its significant deficiency is not common. In advanced stages of insufficient supply, haemorrhage and bleeding may occur.
The main sources of vitamin K2 include fermented foods (e.g. certain cheeses and natto, a Japanese dish prepared from fermented soya beans) ^[15].

Can over-supply of ADEK vitamin complex cause side effects? What is worth paying attention to when taking supplementation?

Because ADEKs are fat-soluble vitamins, the body accumulates them in the body - including in the liver and fatty tissue. Taking too large portions of supplements can therefore be associated with the accumulation of levels of these vitamins in the organs and the occurrence of adverse symptoms, which should arouse our vigilance.
Hypervitaminosis A, i.e. an excess of vitamin A in the body, can manifest itself, for example: severe headaches and dizziness, nausea, blurred vision, impaired motor coordination and muscle pain.
Long-term intake of large portions of vitamin A can contribute to fatigue, depressed mood, dry skin and joint pain ^[2].
Excess vitamin D is dangerous for the body. Because it increases the absorption of calcium in the gastrointestinal tract, too much of the sunshine vitamin can contribute to hypercalcaemia - and this manifests itself in muscle weakness, nausea, vomiting, neuropsychiatric disorders, dehydration and loss of appetite, among other symptoms. In rare and extreme cases, even kidney failure and cardiac arrhythmias can occur. It is worth remembering, however, that excess vitamin D is extremely rare (as are the side effects associated with it) and the vitamin itself is considered a safe substance ^[7].
There is speculation that excessive portions of alpha-tocopherol (vitamin E) may increase the risk of bleeding ^[11]. Vitamin K, on the other hand, has such low toxicity that no adverse effects have been noted from taking it in large amounts ^[15].

Take care of yourself comprehensively - ADEK vitamins from Osavi

Supplementation with a fat-soluble vitamin complex is a good solution for people who are unable to provide adequate amounts of these nutrients with their diet. When reaching for a particular product, it is worth making sure that it meets the basic criteria that determine its effectiveness and safety of use. Osavi ADEK vitamins have been formulated to provide you with the best possible supplementation results - for the sake of your condition. They contain four highly bioavailable forms of the listed vitamins:

• natural beta-carotene from D. salina algae (provitamin A),
• natural vitamin D3 (cholecalciferol),
• natural vitamin E (D-alpha-tocopherol),
• vitamin K2 (menaquinone-7) - more specifically, the highly bioavailable K2VITAL®, a vitamin identical to the K2 molecule found in nature ^[17].

The product comes in the form of easy-to-swallow soft capsules with MCT oil extracted only from the oil produced from the coconut palm fruit Cocos nucifera^[20].
The recommended daily serving corresponds to one capsule, in which you will find up to 800 µg of vitamin A, 12 mg of vitamin E, 75 µg of vitamin K (100% RWS) and 25 µg (1000 IU) of vitamin D3 (500% RWS). We recommend taking the supplement with or immediately after a meal.

[1] Stevens SL. (2021). Fat-Soluble Vitamins. Nurs Clin North Am.;56(1):33-45. doi: 10.1016/j.cnur.2020.10.003. PMID: 33549284.
[2] Vitamin A and Carotenoids. Fact Sheet for Health Professionals. NIH. National Institutes of Health. Office of Dietary Supplements. Pobrano 08.05.2023 z https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/.
[3] Wang, J. et. al. (2022). The Extraction of β-Carotene from Microalgae for Testing Their Health Benefits. Foods, 11, 502. https://doi.org/10.3390/foods11040502.
[4] Stahl W. & Sies H. (2012). β-Carotene and other carotenoids in protection from sunlight. The American journal of clinical nutrition, 96(5), 1179S–84S. https://doi.org/10.3945/ajcn.112.034819.
[5] Köpcke W. & Krutmann J. et. al. (2008). Protection from sunburn with beta-Carotene--a meta-analysis. Photochemistry and photobiology, 84(2), 284–288. https://doi.org/10.1111/j.1751-1097.2007.00253.x.
[6] Havas F. et. al. (2022). A Dunaliella salina Extract Counteracts Skin Aging under Intense Solar Irradiation Thanks to Its Antiglycation and Anti-Inflammatory Properties. Marine drugs, 20(2), 104. https://doi.org/10.3390/md20020104.
[7] Vitamin D. Fact Sheet for Health Professionals. NIH. National Institutes of Health. Office of Dietary Supplements. Pobrano 08.05.2023 z https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/.
[8] Rees JR. et. al. (2013). Vitamin D3 supplementation and upper respiratory tract infections in a randomized, controlled trial. Clin Infect Dis.;57(10):1384-92. doi: 10.1093/cid/cit549.
[9] Hill TR, Aspray TJ. (2017). The role of vitamin D in maintaining bone health in older people. Ther Adv Musculoskelet Dis.;9(4):89-95. doi:10.1177/1759720X17692502.
[10] Verstuyf A. et. al. (2010). Vitamin D: a pleiotropic hormone. Kidney Int.;78(2):140-5. doi: 10.1038/ki.2010.17.
[11] Vitamin E. Fact Sheet for Health Professionals. NIH. National Institutes of Health. Office of Dietary Supplements. Pobrano 08.05.2023 z https://ods.od.nih.gov/factsheets/VitaminE-HealthProfessional/.
[12] Asbaghi O. et. al. (2020). The effect of vitamin E supplementation on selected inflammatory biomarkers in adults: a systematic review and meta-analysis of randomized clinical trials. Sci Rep.;10(1):17234.
[13] Lee GY, Han SN. (2018). The Role of Vitamin E in Immunity. Nutrients. 1;10(11):1614. doi: 10.3390/nu10111614. PMID: 30388871; PMCID: PMC6266234.
[14] Lewis ED. Et. al. (2019). Regulatory role of vitamin E in the immune system and inflammation. IUBMB Life;71(4):487-494. doi: 10.1002/iub.1976. Epub 2018 Nov 30. PMID: 30501009; PMCID: PMC7011499.
[15] Vitamin K. Fact Sheet for Health Professionals. NIH. National Institutes of Health. Office of Dietary Supplements. Pobrano 08.05.2023 z https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/.
[16] Sato T. et. al. (2020). MK-7 and Its Effects on Bone Quality and Strength. Nutrients;12(4):965. doi:10.3390/nu12040965.
[17] The first of its kind: Introducing K2VITAL® MCT Organic. Kappa Bioscience. Pobrano 08.05.2023 z https://www.kappabio.com/.
[18] Siener R. et. al. (2020). Effect of Fat-Soluble Vitamins A, D, E and K on Vitamin Status and Metabolic Profile in Patients with Fat Malabsorption with and without Urolithiasis. Nutrients; 12(10):3110. https://doi.org/10.3390/nu12103110.
[19] Cook MK. et al. (2022). The use of oral vitamin A in acne management: a review. Dermatol Online J.; 15;28(5). doi: 10.5070/D328559239. PMID: 36809126.
[20] MCT oil type V Ph. Eur. Gustav Heess. Group of Companies Since 1897. Pobrano 08.05.2023 z https://www.heessoils.com/en/product/mct-oil-type-v-ph-eur.html.