Fat Soluble Vitamins in Human Nutrition

Vitamins are classified on the basis of their solubility and are categorized into two parts, namely, water soluble vitamins and fat soluble vitamins. Unlike water soluble vitamins, these vitamins are directly absorbed into the body as it does for dietary fats. The known fat soluble vitamin names/ groups are vitamin A, D, E and K. Except for vitamin A, the other fat soluble vitamins are sub-categorized based on their functioning and their availability. As for vitamin D, it is divided into two types depending on its availability, namely vitamin D3 that is found in animals and vitamin D2 that is found in plants such as mushrooms. These are categorized on the basis of fat soluble vitamin function biologically and on the basis of biological functioning of alpha-tocopherol, it is recognized and absorbed in the body. On the other hand, vitamin K has various subcategories that are identified and classified depending on the origin it is generated from. The active forms of all these vitamins have varied potency and not all the active forms are available in dietary sources, some of them are synthesized artificially that is partially absorbed in the body. Now all these fat soluble vitamins are similar in their basic structure and are therefore structurally related. 

The basic molecular structure of all these vitamins contain a molecule of a five-carbon isoprene segment that is shown in the image below:- 

[Image will be Uploaded Soon]

Vitamin A,D,E and K

Vitamin A

Vitamin A, which is the fat soluble vitamin, is not a single compound but is made up of a number of collective compounds known as retinoids and it helps in maintaining healthy vision. The absence of these compounds in dietary supplements may cause loss or damage to vision. The most common form of vitamin A is retinol that is found widely in regular dietary sources. But other forms of vitamin A are retinal and retinoic acid is rarely found or rather absent in dietary foods but are synthesised by the human body. Another form of vitamin A that is less active and is abundantly found in freshwater fish is A2 or dehydroretinal. Vitamin is only generated from animal source and is abundantly found in fish, fish liver oil and butter. An alternate source of vitamin A is the carotenoid antioxidants that are found in the plants but the overall availability is very less. The most effective of plant-based vitamin A is beta-carotene that is abundantly found in carrots, spinach and kale. The availability of 100 grams or 3 ounces of vitamin A, that is, retinol in few of the dietary supplements rich in this vitamin are represented in the following graph.

[Image will be Uploaded Soon]

The recommended intake of vitamin A for different age groups are given below in the following table:

This table shows the upper tolerable intake limit, that is the maximum intake limit of a person per day and is safe for almost 97% of people who are healthy.

Vitamin D

Vitamin D is commonly known as sunlight vitamin as the major natural source to obtain this vitamin is cholecalciferol that is synthesised in the lower layer of the skin epidermis by a chemical reaction that is dependent on UV radiation coming from the sun. cholecalciferol and ergocalciferol are found in very limited dietary supplements such as the flesh of a fatty fish. This vitamin is functional for the absorption of calcium, magnesium and phosphate in the body. Thus it is most beneficial for bone health and deficiency of this vitamin will make the human body susceptible to bone fracture. The main source of vitamin D is sunlight but overexposure to the UV radiation that is responsible for the production of sunlight can cause serious damage to the skin that may lead to skin cancer. Thus the most reliable source for vitamin D are vitamin D drug supplements or naturally growing dietary food such as the flesh of fatty fish, fish oil or the mushrooms that have been exposed to UV radiation under the sun contains a desirable amount of vitamin D.  The availability of 100 grams or 3 ounces of vitamin D, that is, retinol in few of the dietary supplements rich in this vitamin are represented in the following graph.

[Image will be Uploaded Soon]

The following graph shows the regular dietary allowance (RDA) and the upper intake (UI) limit of vitamin D and for infants, adequate intake (AI) is similar to RDA based on weaker evidence. 

Vitamin E

Vitamin E consists of eight components of vitamin out of which four are tocopherols and the rest four are tocotrienols. These are rich antioxidants that protect the cell membrane from the reactive oxygen species. The tocopherol and the tocotrienols, both are present in alpha, beta, gamma and delta forms that are decided by the position and number of methyl groups attached to the cromenol ring.  Thus it has eight types that are occurring naturally out of which only one is recognized by the human body. Thus these fat soluble vitamin names are alpha, beta, gamma-tocopherol and alpha, beta, gamma-tocotrienol. Out of all these eight forms of vitamin E only alpha-tocopherol is absorbed in the human body. This form of vitamin makes 90% of vitamin E in human blood. Deficiency of this vitamin results in cardiovascular diseases, cancer, dementia and other forms of diseases. Vegetable oil, nuts and seeds are the richest dietary source of vitamin E. The below grapes represent the amount of alpha, gamma, beta and delta units of tocopherol is present in 100gms or 900 Kcal of tocopherol extracted from different dietary contents which are mostly natural oils.

[Image will be Uploaded Soon] 

The following graph shows the regular dietary allowance (RDA) and the upper intake (UI) limit of vitamin E and for infants, adequate intake (AI) is similar to RDA based on weaker evidence. 

Vitamin K

Vitamin K belongs structurally similar to the vitamers that are mostly present in the dietary supplements and food easily found in the market. Vitamin K is a necessary component for the human body as it helps in the clotting of blood or for the binding of calcium to the bones and tissues by performing post-synthesis modification of a few proteins that are essential for blood coagulation. There are actually two derivatives of vitamin K that are chemically referred to as 2-methyl-1,4-naphthoquinone(3)-derivatives. The two major natural vitamers of the vitamin K family are vitamin K1 or phylloquinone which is synthesized by plants, members of vitamin K2 (30) or menaquinone are of microbial origin, fermented soy products and mammalian tissues. Vitamin K2 is further subdivided into certain groups that possess different lengths of the side chain of carbon atoms that are made up of isoprenoid groups of atoms. Thus, for vitamin K, the fat soluble vitamin names are vitamin K1 or phylloquinone which is synthesized by plants, members of vitamin K2 (30) or menaquinone are of microbial origin, vitamin K2 (20) is synthesized in mammalian tissues and all other forms of vitamin K is converted from K3 known as menadione to K2 (20). The availability of 100 grams or 3 ounces of vitamin K  in few of the dietary supplements rich in this vitamin is represented in the following graph.

[Image will be Uploaded Soon]

The following graph shows the regular dietary allowance (RDA) and the upper intake (UI) limit of vitamin K and for infants. Adequate intake (AI) is similar to RDA based on weaker evidence. 

Fat Soluble Vitamins Functions

Fat soluble vitamin functions are diverse out of which some of them are mentioned below.

Vitamin A Functions

1. It protects the light sensing cell in the eye and promotes the formation of tear fluid.

2. It promotes immune function in the body.

3. It is an essential component for cell growth and deficiency of it may affect healthy growth among children.

4. Vitamin A is important to maintain fertility in the body and it promotes the development of the fetus.

Vitamin D Function

1. This is an essential vitamin for the absorption and circulation of minerals like calcium, magnesium and phosphorus in the body that helps in bone growth and maintenance.

2. It also regulates as well as provides strength to the immune system of the body.

3. Once it enters the liver and kidney through the bloodstream, they change calciferol to calcitriol that can be stored in the body for later use in the form of calcidiol. Calcitriol is actually the active form of vitamin D

Vitamin E Function 

1. This is a very strong antioxidant that prevents the cell membrane and the fatty acids in the cell membrane from any active oxygen agents.

2. It also prevents our body from any oxidative stress.

3. High amounts of vitamin E acts as blood thinner thus helps to prevent and dissolve any irregular blood clots formed in the body. The antioxidant property is enhanced by other nutrients like vitamin A and B3.

Vitamin K Function

1. Vitamin K supports bone health, prevents calcification of blood vessels and partially reduces the risk of heart disease.

2. The main function of vitamin K is to clot blood in the body thus preventing unnatural severe blood loss due to any wound.

Fat Soluble Vitamin Supplement Benefits

Benefits of Vitamin A Supplements 

Vitamin A supplements are required in the diets of those who suffer from a deficiency of vitamin A in their body due to the lack of dietary as well as food components in the regular diets. In studies, it has been established that vitamin A supplements help treat measles in children and also prevent pneumonia that occurs due to the measles virus and reduce the death percentage by 50 -80%. Intake of vitamin A suppresses the virus causing measles.

Benefits of Vitamin D Supplements

People spending less time under sunlight may acquire a vitamin D deficiency but taking up dietary supplements like fatty fish skin or liver, mushrooms etc can fulfill the need for vitamin D in the body. It helps unwell elderly people who are institutionalized or hospitalized to extend their lifespan while maintaining a healthy system. Regular intake of vitamin D reduces the risk of respiratory problems.

Benefits of Vitamin E Supplements

Vitamin E food supplements, especially gamma tocopherol helps in increasing blood flow in the body by dilating the blood vessels and hence reduce blood pressure and risk of heart failure. Gamma tocopherol has blood thinning properties and thus prevents blood clots in the body and also helps in reducing bad LDL cholesterol.

Fat Soluble Vitamin Deficiency

Deficiency of Vitamin A:

1. Dry Eyes - deficiency of vitamin A causes less production of tear fluid that may cause dry eyes that lead to a severe condition of the eye called xerophthalmia.

2. Blindness - serious deficiency of vitamin A for a prolonged period of time may cause total blindness and it is one of the major and most common causes of blindness in the world.

3. Skin Problem - deficiency of vitamin A leads to a typical skin problem called goose or hyperkeratosis.

4. Poor Immune Function - deficiency of vitamin A makes people prone to various chronic infections like cough and cold. 

Deficiency of Vitamin D:

1. Vitamin D deficiency leads to poor immune functions that increase the chances to acquire autoimmune disease and various infections. This is very common in elderly people who are institutionalized or hospitalized.

2. Vitamin D deficiency leads to soft bone, weak muscle and bone fractures. This condition is commonly known as rickets in children and osteomalacia among adults. 

3. Its deficiency leads to darkening of skin colour, old age, obesity etc.

Deficiency of Vitamin E: 

Vitamin E, which is a fat soluble vitamin, deficiency is less common in healthy people but little deficiency may lead to muscle weakness, poor immunity, vision problem, tremors, difficulty in walking and numbness. A prolonged deficiency of vitamin E can cause amnesia, dementia, poor reflexes and losing the ability to control the full movement of the body.

Deficiency of Vitamin K:

1. The deficiency of vitamin K leads to lower bone density and increased risk of fractures in women.

2. The inability to efficiently digest and absorb fat in the body gives rise to the deficiency of vitamin K which results in cystic fibrosis, inflammatory bowel disease and celiac disease.

3. The use of high dosage of vitamin A, as well as the consumption of broad-spectrum antibiotics, lead to a deficiency of vitamin K in the body.