Importance of Fat-soluble Vitamins (A, D, E & K) to Health and Wellness

Vitamins can be categorized on the basis of their solubility. Most of them are water-soluble, which means they dissolve in water. On the other side, fat-soluble vitamins are similar to oil and do not dissolve in water. Fat-soluble vitamins are the most abundant in high-fat foods and are much more absorbed in your bloodstream when you eat them with fat. There are four fat-soluble vitamins in our diet, they are Vitamin A, Vitamin D, Vitamin E and Vitamin K.

Vitamin A

Vitamin A plays a crucial role in sustaining our sight. Without it, we’d go blind. Vitamin A is best known for its vital role in maintaining vision. It’s also essential for body growth, immune function and reproductive health. Vitamin A is not just a single compound. Instead, it is a group of fat-soluble compounds commonly known as retinoids. Retinol is the most popular dietary source of vitamin A. Other forms (retinal and retinoic acid) are present in the body, but are absent or rare in food.

Dietary Sources of Vitamin A

People can get vitamin A from dietary sources. Animal sources include preformed vitamin A or retinols. This type is ready for use by the body. Plant sources include carotenoids, such as beta-carotene, which is a potent antioxidant. They can be processed into vitamin A by the body. Animal sources of vitamin A include fish liver oil, beef liver, cheese, milk, and other dairy products. While sources of beta carotene include sweet potato, kale, spinach, and other green, leafy vegetables, carrots, cantaloupe, black-eyed peas and fortified breakfast cereals.

Functions of Vitamin A in the Body

Vitamin A supports many critical aspects of body function, including:

• Body growth: Vitamin A is necessary for cell growth. Deficiency may slow or prevent growth in children.
• Hair growth: It is also vital for hair growth. Deficiency leads to alopecia, or hair loss.
• Reproductive function: Vitamin A maintains fertility and is vital for fetal development.
• Vision maintenance: Vitamin A is essential for maintaining the light-sensing cells in the eyes and for the formation of tear fluid.
• Immune function: Vitamin A deficiency impairs immune function, increasing susceptibility to infections.

Recommended Daily Allowance (RDA) for Vitamin A

The recommended daily allowance (RDA) for vitamin A is as shown in the table below. RDA is the average amount of vitamin A that the vast majority (about 97.5%) of people need to satisfy their daily requirements. This table also displays the tolerable upper intake limit (UL), the maximum level of dietary intake considered acceptable for 97.5 per cent of healthy people.

Common Symptoms Associated with Vitamin A Deficiency

In developed countries, vitamin A deficiency is rare. However, vegetarians may be at risk, as pre-formed vitamin A can only be contained in animal-based foods. While provitamin A is abundant in many fruits and vegetables, it is not always effectively converted to retinol, the active form of vitamin A. The success of this conversion depends on the biology of humans.

Deficiency is also common in some developing countries where there is little food diversity. It is normal in populations whose diet is dominated by processed rice, white potatoes or cassava and lack of meat, fat and vegetables. A common symptom of early deficiency is night blindness. If it progresses, it can lead to more severe conditions, such as:

• Hair loss: If you are vitamin A deficient, you may start to lose your hair.
• Skin problems: Deficiency leads to a skin condition known as hyperkeratosis or goose flesh.
• Poor immune function: Poor vitamin A status or deficiency makes people prone to infections.
• Dry eyes: Severe deficiency may cause xerophthalmia, a condition characterized by dry eyes caused by reduced tear fluid formation.
• Blindness: Serious vitamin A deficiency may lead to total blindness. In fact, it is among the most common preventable causes of blindness in the world.

Vitamin D

Vitamin D, also referred to as sunshine vitamin, is released by the skin when exposed to sunlight. It is best known for its beneficial effects on bone health, and deficiency makes a person highly susceptible to bone fractures. Vitamin D is a collective term used to describe a variety of similar fat-soluble compounds. Vitamin D, also known as calciferol, comes in two main dietary types, namely:

• Vitamin D2 (ergocalciferol): Found in mushrooms and some plants.
• Vitamin D3 (cholecalciferol): Found in animal-sourced foods, such as eggs and fish oil, and produced by your skin when exposed to sunlight.

Sources of Vitamin D for the Body

The body will produce all the vitamin D that it requires as long as the skin is consistently exposed to sunlight. However, many people spend no time in the sun, or they do so fully clothed. Justifiably, some cover their skin with sunscreen to avoid sunburn. While sunscreen use is highly recommended, it reduces the amount of vitamin D provided by the skin. As a result, people usually need to rely on their diet to get enough vitamin D. Few foods naturally contain vitamin D, including oily fish and fish oils, beef liver, eggs, fortified dairy products, vegetables milk and cereals.

Functions of Vitamin D in the Body

Vitamin D has numerous functions which include but not limited to the following:

• Maintaining of Bones: Vitamin D controls the circulating levels of calcium and phosphorus, which are the most essential minerals for bone growth and maintenance. It facilitates the absorption of these minerals in the diet.
• Regulation of Immune System: It also regulates and strengthens immune system function

Recommended Dietary Allowance (RDA) for Vitamin D

The following table shows the recommended dietary allowance (RDA) and the upper limit (UI) for vitamin D. Since no RDA has been defined for children, the values marked with an asterisk are the adequate intake (AI).⠀

Causes and Effects of Vitamin D Deficiency

Severe deficiency of vitamin D is rare, but mild forms of deficiency or insufficiency are common in both hospitalized and elderly individuals. Dark skin colour, old age, obesity, low sun exposure and diseases that impair fat absorption are risk factors of deficiency. Soft bones, weak muscles and an increased risk of bone fractures are among the most well-known consequences of vitamin D deficiency. This condition in adults is called osteomalacia, and in children, rickets.

Poor immune function, increased susceptibility to infections, and autoimmune diseases are also associated with vitamin D deficiency. Fatigue, depression, hair loss and impaired wound healing may include other signs of deficiency or insufficiency. Low vitamin D or deficiency levels have also been linked to an increased risk of dying from cancer and an increased risk of heart attacks in observational studies.

Vitamin E

Vitamin E is an antioxidant that can help the body to destroy free radicals. Free radicals are unstable atoms which can cause oxidative stress. Oxidative stress can lead to cell damage, which can lead to cancer and other diseases. Vitamin E can help protect the body from a range of health problems. As a powerful antioxidant, vitamin E protects your cells from premature aging and free radical damage.

Vitamin E is a family of eight structurally similar antioxidants divided into two groups:

• Tocopherols: Alpha-tocopherol, beta-tocopherol, gamma-tocopherol and delta-tocopherol.
• Tocotrienols: Alpha-tocotrienol, beta-tocotrienol, gamma-tocotrienol and delta-tocotrienol.

However, it is important to note that alpha-tocopherol is the most common type of vitamin E that makes up about 90% of vitamin E in the blood.

Dietary Sources of Vitamin E

Vitamin E is naturally present in foods and is added to certain fortified foods. The recommended quantities of vitamin E can be obtained by consuming a variety of foods, including the following:

• Green vegetables, such as spinach and broccoli, provide some vitamin E.
• Food companies add vitamin E to some breakfast cereals, fruit juices, margarines and spreads, and other foods. To find out which ones have vitamin E, check the product labels.
• Vegetable oils like wheat germ, sunflower, and safflower oils are among the best sources of vitamin E. Corn and soybean oils also provide some vitamin E.
• Nuts (such as peanuts, hazelnuts, and, especially, almonds) and seeds (like sunflower seeds) are also among the best sources of vitamin E.

Recommended Daily Allowance (RDA) for Vitamin E

The table below shows the RDA and the tolerable upper limit of vitamin E intake. Adequate intake is indicated with an asterisk, since there are no RDA values available for infants.

Functions of Vitamin E in the Body

Vitamin E is a fat-soluble mineral present in a variety of foods. It functions as an antioxidant in the body, helping to protect cells from damage caused by free radicals. Free radicals are compounds formed as our bodies turn the food we consume to energy. People are often exposed to free radicals in the atmosphere through tobacco smoke, air pollution, and sunlight.

The body also requires vitamin E to strengthen its immune system so that it can fend off infectious bacteria and viruses. In high quantities, vitamin E also serves as a blood thinner by expanding the blood vessels and stopping blood from clotting within them. In addition, the cells use vitamin E to communicate with each other and perform several essential functions.

The key function of vitamin E is to act as an antioxidant, to avoid oxidative stress and to protect fatty acids from free radicals in the cell membranes. Other nutrients, such as vitamin C, vitamin B3 and selenium, improve these antioxidant properties.

Causes and Effects of Vitamin E Deficiency in the Body

Vitamin E deficiency is rare and is never detected in people who are otherwise healthy. It is almost always associated with certain diseases in which fat is not properly digested or absorbed. It occurs most often in diseases that impair the absorption of fat or vitamin E from food. Examples include Crohn’s disease, cystic fibrosis, and some rare genetic diseases such as abetalipoproteinemia and vitamin E deficiency ataxia (AVED). Vitamin E needs some fat to be absorbed by the digestive system.

Vitamin E deficiency can cause nerve and muscle damage, resulting in loss of feeling in the arms and legs, loss of body movement control, walking difficulties, tremor, muscle weakness, and vision problems. A weakened immune system is another sign of deficiency. Severe, long-term deficiency can lead to anemia, heart disease, serious neurological problems, blindness, dementia, poor reflexes and an inability to fully control body movements.

Common Effects of Vitamin E on Health

Scientists are researching vitamin E to understand how it affects health. Here are a few examples of what this study has revealed.

Vitamin E and Heart Disease

Some studies link higher intakes of vitamin E from supplements to lower risk of coronary heart disease. But the best study has almost no impact. People in these studies are randomly assigned to take vitamin E or placebo (a dummy pill without vitamin E or active ingredients) and do not know what they are taking. Vitamin E supplements do not appear to prevent, minimize or affect the risk of death from heart disease. Scientists do not know if high vitamin E intakes may protect the heart of younger, healthier people who do not have a high risk of heart disease.

Vitamin E and Cancer

Most studies shows that vitamin E does not help prevent cancer and can be harmful in some cases. Significant doses of vitamin E have not consistently decreased the risk of colon and breast cancer, for example, in research. A major study found that taking vitamin E supplements (180 mg/day [400 IU]) has raised the risk of developing prostate cancer in men for many years. Two studies that tracked middle-aged men and women for 7 years or more found that extra vitamin E (201−268 mg/day [300–400 IU] on average) did not protect them from any form of cancer. However, one study found a correlation between the use of vitamin E supplements for 10 years or more and a lower risk of death due to bladder cancer.

Vitamin E dietary supplements and other antioxidants can interfere with chemotherapy and radiation therapy. People undergoing these treatments need a doctor’s advice before taking vitamin E or other antioxidant supplements, especially at high doses.

Vitamin E and Eye Disorders

Age-related macular degeneration (AMD) or loss of central vision in older people and cataracts are among the most common causes of loss of vision in older people. The findings of research into whether vitamin E can help prevent these conditions are contradictory. For those with AMD who were at high risk of developing advanced AMD, a supplement containing high doses of vitamin E along with other antioxidants, zinc and copper showed a potential to slow down the rate of vision loss.

Vitamin E and Mental function

Several studies have investigated whether vitamin E supplements can help older adults to remain mentally alert and active, as well as to prevent or slow down mental function and Alzheimer’s disease. To date, research has provided little evidence that taking vitamin E supplements will help healthy people or people with minor mental health issues to maintain their brain health.

Vitamin K

Vitamin K helps the body to form blood clots. Blood clotting is important to avoid excess bleeding. Vitamin K is needed by the human body for the post-synthesis modification of certain proteins required for blood coagulation or for the regulation of calcium binding in bones and other tissues. Without it, a person would be at risk of bleeding to death. In reality, vitamin K is a group of fat-soluble compounds divided into two main groups:

• Vitamin K-1 (phylloquinone), present in green, leafy vegetables and some other plant sources
• Vitamin K-2 (menaquinones), present in animal sources and fermented foods

There are also synthetic forms and other forms that the body makes. Additionally, there are at least three synthetic forms of vitamin K. These are known as vitamin K3 (menadione), vitamin K4 (menadiol diacetate) and vitamin K5.

Sources of Vitamin K for the Body

Food sources of phylloquinone include fruits, in particular green leafy vegetables, vegetable oils and some fruits. Meat, dairy foods and eggs contain low levels of phylloquinone but low levels of menaquinone. Natto (a popular Japanese food made from fermented soybeans) has high levels of menaquinone. Other fermented foods, such as cheese, also contain menaquinone. However, the types and quantities of vitamin K in these foods are likely to vary depending on the bacterial strains used to make the food and the fermentation conditions. Animals synthesize MK-4 to menadione (a synthetic form of vitamin K that can be used in poultry and swine feed). Thus, poultry and pork products produce MK-4 when menadione is introduced to the feed of the animal.

Recommended Daily Allowance (RDA) for Vitamin K

The table below shows the adequate intake (AI) values for vitamin K. AI is comparable to Recommended Daily Allowance (RDA), which is a daily consumption standard that is thought to meet the requirements of 97.5 per cent of people, but AI is based on less evidence than RDA.

Functions of Vitamin K in the Body

Vitamin K plays a crucial role in blood clotting. In essence, the word “K” stands for “koagulation,” the Danish word for coagulation, which means clotting. However vitamin K also has other functions, including improving bone health and helping reduce calcification of blood vessels, potentially reducing the risk of heart disease.

Causes and Effects of Vitamin K Deficiency

In comparison to vitamins A and D, vitamin K is not processed in large quantities in the body. For this reason, consuming a diet which lacks vitamin K  may lead you to become deficient in as little as a week. People who do not digest and consume fat adequately are at the highest risk of developing vitamin K deficiency. This includes those suffering from celiac disease, inflammatory bowel disease and cystic fibrosis.

The use of broad-spectrum antibiotics can also increase the risk of deficiency as well as very high doses of vitamin A, which tend to minimize the absorption of vitamin K. Mega doses of vitamin E can also reduce the effects of vitamin K on blood clotting. Without vitamin K, your blood wouldn’t clot, and even a small wound could cause a ceaseless bleeding. Fortunately, vitamin K deficiency is uncommon, since the body only requires small quantities to sustain blood clotting. Low levels of vitamin K have also been associated with decreased bone density and increased risk of fractures in women.