What Do Fat-Soluble Vitamins Do In Our Body?

Table of Contents (click to expand)

The fat-soluble vitamins (vitamins A, D, E & K) are required for various physiological processes, such as blood coagulation, bone metabolism and eyesight.

Imagine a hearty morning breakfast laid out on a bright sunny day. On the table are eggs and bacon, milk and bread, ready made and waiting for you. There’s even some freshly squeezed orange juice to go with it. Who wouldn’t want to start the day like this? This breakfast table would please both doctors and patients alike. Know why? The foods on it is full of vitamins, which make doctors happy, and are also delicious, which makes you happy.

From a healthy heart, youthful skin and strong bones to shiny hair, smart brains and pink nails, vitamins are responsible for them all. There are a total of 13 essential vitamins required to keep the body in top form.

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Fat-soluble Vitamins

Of the 13 known vitamins, nine are water-soluble and four are fat-soluble. The fat-soluble vitamin are A, D, E and K.

Being fat-soluble, scientifically called lipophillic, these vitamins are stored in the fatty tissue—the adipose tissue—of our body. Since they can be stored, we don’t need to frequently supplement them into our diet.

However, the same property that makes them easy to store also makes them difficult to transport. These fat-soluble vitamins need additional carrier proteins to transport them through the watery contents of our blood. This is important, since a mutation in these carrier proteins can lead to vitamin deficiency.

Also Read: Why Is It Possible To Overdose On Some Vitamins But Not Others?

Vitamin A

Vitamin A is the collective term for a group of compounds called retinoids, which come in a few different forms—retinol, beta-carotene and carotenoids. These compounds play a role in the processes of the immune system, wound healing, and bone growth, but by far the most discussed role of vitamin A is that of good eyesight.

To see in the dark, our eyes require a pigment called rhodopsin. For rhodopsin to work in the dark, it needs vitamin A. More specifically, it needs the retinol form of vitamin A. When light strikes retinol, it changes retinol’s structure, which triggers a signaling pathway that sends a signal to the eye cells, informing them that there is light. The eye cells then send this signal to the brain via the optic nerve.

Do you know why carrots are good for the eyes? Because carrots get their orange-red color from beta-carotene.

Vitamin A is also known to slow down skin aging, making it a popular cosmetic ingredient. Retinoids have anti-wrinkle properties, as they promote skin cell growth, help keep the skin hydrated and protect against collagen degradation.

Leafy greens, egg yolk and fish are all excellent sources of this vitamin. The liver of animals is the storehouse of vitamin A, and therefore makes a good source of vitamin A.

Carrot juice(pilipphoto)s
Orange and carrot juice is an excellent combination and provides both vitamin A and C (Photo Credit : pilipphoto/Shutterstock)

Also Read: Know Your Vitamins: What Do Water-Soluble Vitamins Do In The Body?

Vitamin D

If there is one vitamin with the most reported deficiencies, it is Vitamin D. We get Vitamin D from sunlight, but our urban lifestyle keeps many of us indoors, limiting our exposure to sunshine.

You must wonder how sunlight, made up of photons, results in chemical vitamins we need to survive. The sun’s rays don’t give us the chemical Vitamin D, but rather converts another chemical into the vitamin. The sun emits UV rays that penetrate our skin layers, where it breaks down a compound known as 7-dehydrocholesterol into vitamin D.

When we are on the beach on a sunny day, we rub some sunscreen over our bodies to prevent painful sunburn. The sunscreen blocks the harmful UV rays from passing through our skin. However, it also blocks the UV rays required for our bodies to synthesize vitamin D in the skin. The higher the SPF of the sunscreen, the greater the percentage of UV rays it blocks. With this being said, sunscreen is important, as it also protects us from harmful UV rays that cause cancer.

This is the same reason that sunlight coming through glass doesn’t help, since glass tends to block out these UV rays.

Vitamin D is vital for our bones and muscles. Known as cholecalciferol, vitamin D works in conjunction with calcium and phosphorous to optimize bone density.

Eggs and fish oils are rich in this strengthening vitamin, while the vegan option would be taking generous dollops of sunlight directly to the skin. Most of the vitamin D that the majority of people acquire is from sunshine, rather than dietary sources.

Summer sunny lifestyle fashion portrait of young stylish hipster woman walking on street(Diana Indiana)s
Soaking up some sunlight can be great for your vitamin D levels. (Photo Credit : Diana Indiana/Shutterstock)

Vitamin E

Vitamin E, also known as tocopherol, has eight possible forms, the most common of which is alpha (α) tocopherol.

This nutrient is an antioxidant and protects the body’s cells from the harmful effects of free radicals. The vitamin is crucial for our nervous system, skeletal muscle and retina.

It also prevents blood vessels from becoming clogged with plaque. This plaque is nothing but fatty deposits, and when these build up in the arteries, it leads to atherosclerosis. However, the exact role of how vitamin E prevents atherosclerosis is still unclear.

Fat-containing foods, such as fish, egg yolks, almonds and peanut butter, can also be your go-to for regular doses of this vitamin. Seed oils, such as those from sunflower and mustard, are also rich in vitamin E. Adding large amounts of red and green peppers, spinach and beet greens to your diet will also supply you with sufficient amounts of Vitamin E.

The general consensus is that vitamin E is required for vitamin A to be utilized optimally. Studies have shown that if a diet contains adequate amounts of vitamin E, then more vitamin A is stored in the liver.

Vitamin K

The K in vitamin K could very well stand for ‘Keeping us alive’, as this vitamin keeps the blood from endlessly oozing out when we get hurt.

This vitamin comes in two forms: plant-derived K1, phylloquinone and bacteria-derived K2, menaquinones. We need both these forms of vitamin K. Proteins that help clot our blood, such as prothrombin, need phylloquinone to function.

K1 comes from our diet, but K2 is equally important; it might help us absorb and use nutrients better, as well as help children grow healthy. Lactic acid bacteria present inside our intestines synthesize vitamin K mainly for their own metabolic purposes. However, we humans can also use the bacterial form of vitamin K for ourselves. In fact, our intestinal bacteria are believed to maintain the vitamin K level in our bodies.

The best sources of vitamin K are spinach, broccoli, cabbage and brussels sprouts (basically, any green leafy vegetables), cauliflower, eggs, and—thankfully—cheese! Of course, this only applies to fresh cheese, not the processed kind. Some vegetable oils, such as rapeseed oil and olive oil, also contain good amounts of vitamin K1.

Foods highest in Vitamin K on a wooden board(Tatjana Baibakova)s
Foods rich in vitamin K. (Photo Credit : Tatjana Baibakova/Shutterstock)


Fat-soluble vitamins play their part in a variety of physiological processes, such as maintaining your eyesight, improving bone health, aiding blood clotting, and keeping the immune system in fighting shape. All these bodily functions are mandatory for a healthy life.

The best way to obtain these precious health-protecting vitamins is from our food, which is why a healthy and balanced diet consisting of fruits, vegetables, and nuts is indispensable.

If required, don’t hesitate to consult your doctor to find the supplements best suited to your health needs. There are a multitude of vitamin supplements available on the market nowadays, and most come in a wide range of concentrations and flavors!

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References (click to expand)
  1. Leaf, A., & Lansdowne, Z. (2014). Vitamins - Conventional Uses and New Insights. Nutritional Care of Preterm Infants. S. Karger AG.
  2. (2016) Fat-Soluble Vitamins: Clinical Indications and Current ... - NCBI. The National Center for Biotechnology Information
  3. Vitamins & minerals - Healthy Kids Association. healthy-kids.com.au
  4. Listing of vitamins - Harvard Health. Harvard University
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About the Author

Armaan Gvalani holds a Masters in Biotechnology from Symbiosis International University (India). He finds the microscopic world as fascinating as the business of biology. He loves to find practical applications from scientific research. When not peering into his microscope or nurturing his cultures, he can be found smashing a ball around the squash court or doing laps in a pool.