The Four Fat-Soluble Vitamins – Vitamin A, D, E and K

Updated: January 19, 2024

Vitamins and minerals play a wide range of roles in your body to keep your cells, tissues, and organs functioning optimally. While these groups of nutrients tend to be lumped together, vitamins play vastly different roles than minerals. And furthermore, each vitamin has its own unique list of duties depending on its structure, function, and chemical breakdown.

And then comes the water-soluble versus fat-soluble aspect. You’ve probably heard of fat-soluble and water-soluble vitamins, but what exactly does that mean?

This article will highlight the four fat-soluble vitamins, describe their primary functions, and explain why each of these nutrients is vital for bone health.

What Are The 4 Fat-Soluble Vitamins?

The four fat-soluble vitamins include vitamins A, D, E, and K.

The solubility of a vitamin (water versus fat) comes down to the structure of the vitamin, which indicates how each nutrient is absorbed and where it’s stored. 

The water-soluble vitamins (B and C) are dissolved in water and, therefore, easily excreted. 

Fat-soluble vitamins, on the other hand, are dissolved in fat. This means that in order to absorb them, you need fat in the matrix of your food, and once they’re absorbed into your tissues, they can build up over time as they get stored with your fat.

For this reason, it’s much more common for people to experience fat-soluble vitamin toxicity than water-soluble vitamin toxicity. 

The Main Functions of Fat-Soluble Vitamins

Fat-soluble vitamins perform a range of vital activities in your body. Below are some of the main functions that each of the vitamins is responsible for. 

Vitamin A

Vitamin A plays a crucial role in cell growth and differentiation, contributing to the normal formation and maintenance of the heart, lungs, eyes, and other organs. Vitamin A is also involved in[1][2]:

  • Immune function
  • Cellular communication
  • Growth and development
  • Male and female reproduction

Vitamin D

Along with its vital role in bone health (to be discussed more below), vitamin D is involved in[3]:

  • Reduction of inflammation
  • Cellular growth
  • Neuromuscular function
  • Immunity 
  • Glucose metabolism 

Vitamin E

Vitamin E is most well-known as an antioxidant. In fact, “vitamin E” is actually a term used for a collective of fat-soluble compounds with distinctive antioxidant activities. In addition to its role as an antioxidant, vitamin E is also involved in[4]:

  • Gene expression
  • Cell signaling 
  • Immunity
  • Inhibition of platelet aggregation
  • Reducing inflammation

Vitamin K

Vitamin K plays an important role in blood clotting but also assists with:

  • Regulating blood calcium levels
  • Facilitating energy production
  • Maintaining heart health

In addition to each of their individual contributions, the fat-soluble vitamins work in concert with each other to balance one another and improve overall health and vitality. 

For example, studies suggest that vitamin A can reduce the risk of vitamin D toxicity and vice versa. Similarly, adequate levels of vitamin K may decrease symptoms of vitamin A and E toxicity[5][6].

Therefore, each of the four fat-soluble vitamins is not only necessary to human health, but their ratios and proper intakes are also vitally important as they all work synergistically with one another.

The Fat-Soluble Vitamins and Bone Health

Vitamin D

Vitamin D is unique in that, traditionally, the best way to get vitamin D is through sunlight. Unfortunately, today most people spend the majority of their time indoors. Furthermore, studies show that even if you do spend a fair amount of time outside, depending on the latitude of where you live you may not be getting any vitamin D absorption. For instance, one study found that in certain areas of the Northern US, sun exposure during the months of November to February results in zero vitamin D synthesis[7]. 

For both of these reasons, vitamin D supplementation is becoming commonplace.

Vitamin D is vitally important for bone health. Specifically, this vitamin plays a role in regulating circulating calcium and phosphorus levels by enhancing their absorption from food. Calcium and phosphorus are two of the most important minerals for bone health and integrity, which means that when vitamin D is low, it puts your bones at risk for bone mineral density loss and the potential development of osteoporosis or fractures[8]. 

Vitamin D comes in two forms, D2 and D3. While D2 is found in mushrooms and in small amounts in other plants, D3 comes from animal sources like eggs and fish. Of the two, D3 is much more readily absorbed and utilized[9]. 

Vitamin E

Vitamin E is one of the most potent fat-soluble antioxidants and plays a crucial role in protecting the membrane of your cells from free radicals and oxidative damage. 

Studies show that vitamin E may help protect against osteoporosis due to several different mechanisms[10]:  

  • First, there is evidence that vitamin E may enhance osteoblast activity (the bone cells that are responsible for creating new bone in place of old bone). 
  • Second, cell studies show that vitamin E may enhance the proliferation of mesenchymal stem cells (MSCs), which are found in bone marrow and are responsible for making and repairing skeletal tissues.
  • Third, studies show that vitamin E may suppress the formation of osteoclast cells (the cells responsible for breaking down bone). 

Furthermore, a clinical study found that women with low vitamin E levels during postmenopause were at greater risk for developing osteoporosis[11]. 

Vitamin K

There are two forms of vitamin K, K1 and K2. While vitamin K1 plays an essential role in blood clotting, vitamin K2 is the form that is vital for bone health.

Specifically, Vitamin K2 directs calcium into your bones and away from your arteries, assisting in both bone and heart health. When vitamin K2 is low, it can lead to arterial calcification, which sets the stage for cardiovascular disease. When you have balanced levels of vitamin K2, on the other hand, it keeps your arteries clear of excess calcium while also helping your bones maintain their mineral density. 

A common misunderstanding is that excess calcium supplementation increases arterial calcification when, in fact, studies show that it’s a lack of vitamin K2 that is likely the culprit[12]. 

Vitamin K2 is also involved with the production of osteocalcin in your bones, which helps to keep your bones strong. This may be why research shows that low vitamin K2 levels are linked to low bone mineral density[13]. 

Vitamin A

The proper balance of vitamin A is essential to bone health, as both too much and too little may increase your risk of fractures. As mentioned previously, all four fat-soluble vitamins are needed to balance one another, so making sure that you’re getting enough vitamins D, E, and K will also help you maintain a proper ratio of vitamin A. 

Studies indicate that adequate vitamin A through food or supplements helps to maintain healthy bones through this nutrient’s impact on bone cell formation.

Furthermore, research shows that poor bone health outcomes due to high levels of vitamin A are more pronounced in individuals with vitamin D deficiency, indicating that it may not be vitamin A itself causing an issue but rather an imbalance in fat-soluble vitamins[14]. 

The Recommended Intakes for Fat-Soluble Vitamins

As mentioned, these four vitamins work synergistically with one another to optimize their balance and enhance each other’s function. As such, it’s important to get the right amount of each nutrient in a balanced ratio depending on your age and gender. 

Below are the recommended daily intakes for each fat-soluble vitamin.

Vitamin A: 700 mcg/day for adult females and 900 mcg//day for adult males[15]. 

Vitamin D: The National Institute of Health recommends that adults under 71 need 600 IU daily, with that number increasing to 800 IU for adults over the age of 71. However, this dosage may be a bit conservative as The International Osteoporosis Foundation recommends a higher dose of 800-1000 IU daily for adults over 60[16]. 

Getting at least 800 IU per day is a good idea for anyone concerned about bone health.

Vitamin E: 15 mg/day for females and males over the age of 14. Taking more in excess does not result in any added benefits[17]. 

Vitamin K: 90 mcg/day for females 19 and older and 120 mcg/day for males 19 and older[18]. 


While getting a balance of nutrients in your diet is always important, when it comes to the fat-soluble vitamins, it’s even more essential. Due to their ability to impact one another, maintaining a healthy balance of these nutrients is crucial not only for bone health but for the health of all of your organ systems. 

Sign up for the AlgaeCal Newsletter to learn more about what your body needs to maintain optimal bone health.


What does vitamin A do for the body?

Vitamin A contributes to the normal formation and maintenance of the heart, lungs, eyes, and other organs. Vitamin A also assists in immune function, cellular communication, growth, development, and male and female reproduction. 

What does vitamin K do for the body?

Vitamin K plays a vital role in blood clotting and also assists with regulating calcium levels, facilitating energy production, and maintaining heart health. There are two forms of vitamin K, K1 and K2. While vitamin K1 plays an essential role in blood clotting, vitamin K2 is the form that is vital for bone health.

What does vitamin E do for the body?

Vitamin E is most well-known for its antioxidant activity, but it also plays a role in gene expression, cell signaling, immunity, inhibition of platelet aggregation, and the reduction of inflammation. 

What does vitamin D do for the body?

Vitamin D plays a vital role in bone health by helping to regulate calcium and phosphorus levels. It also assists in cellular growth, neuromuscular function, immunity, glucose metabolism, and the reduction of inflammation. 

When should you take fat-soluble vitamins?

Fat-soluble vitamins will be best absorbed when you take them with food. Particularly meals that include fat, as these nutrients require fat for their absorption. 


  1. Sommer, Alfred. “Xerophthalmia and vitamin A status.” Progress in retinal and eye research 17.1 (1998): 9-31. 
  5. Frigg, M., and J. Broz. “Relationships between vitamin A and vitamin E in the chick.” International Journal for Vitamin and Nutrition research. Internationale Zeitschrift fur Vitamin-und Ernahrungsforsch
  7. Webb, A.R., et al. “Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin.” J Clin Endocrinol Metab (1988): 373-378.
  8. DeLuca, Hector F. “The metabolism and functions of vitamin D.” Steroid Hormone Resistance (1986): 361-375.
  9. Shieh, Albert, et al. “Effects of high-dose vitamin D2 versus D3 on total and free 25-hydroxyvitamin D and markers of calcium balance.” The Journal of Clinical Endocrinology & Metabolism 101.8 (2016): 3070-3078.
  10. Wong, Sok Kuan, et al. “The molecular mechanism of vitamin E as a bone-protecting agent: a review on current evidence.” International journal of molecular sciences 20.6 (2019): 1453.
  11. Mata-Granados, José M., et al. “Lower vitamin E serum levels are associated with osteoporosis in early postmenopausal women: a cross-sectional study.” Journal of bone and mineral metabolism 31.4 (2013): 455-460.
  12. Beulens, Joline WJ, et al. “High dietary menaquinone intake is associated with reduced coronary calcification.” Atherosclerosis 203.2 (2009): 489-493.
  13. Weber, Peter. “Vitamin K and bone health.” Nutrition 17.10 (2001): 880-887.
  14. Yee, Michelle Min Fang, et al. “Vitamin A and bone health: a review on current evidence.” Molecules 26.6 (2021): 1757.

Article Comments

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  1. Pauline Harmon

    December 9, 2014 , 7:50 pm

    I have osteoporosis and am taking algaecal and strontium, but I also have an advanced case of glaucoma with much vision loss. very large doses of vitamin A have been recommended to try to protect from more vision loss, also large doses of vitamin C to help keep eye pressure down. After reading this about needing to balance vitamins, how can I manage that with my condition? Pauline

  2. Monica

    December 10, 2014 , 10:08 am

    Hi Pauline,

    That’s a good question for your doctor.

    Research suggests that as long as you are not exceeding the tolerable upper limit, your body should be equipped to take care of balancing the large doses of vitamin C and vitamin A by either storing or flushing them out as needed. Remember that fat soluble vitamins will be stored in your fatty tissues until the body needs them (as noted in the article). And vitamin C, which is a water soluble vitamin, will be flushed out by your body if it there is too much and it is not needed.

    Hope this helps!

    – Monica @ AlgaeCal

  3. Tisha Rose

    December 10, 2014 , 5:23 am

    I have been taking AlgaeCal for four years… a hair analysis shows that I do not have hardly any magnesium. My calcium (10.4)is going to my blood and not to my bones? (I am 76 yrs old – tests show no para thyroid, etc.)

    Why is magnesium usually considered as not very important?

  4. Monica

    December 10, 2014 , 8:46 am

    Hi Tisha,

    Dietary calcium intake should not stay in the blood and added vitamin K2 in AlgaeCal directs calcium straight to your bones. As for your lack of magnesium, AlgaeCal’s recommended daily dose (4 capsules) gives you 350 mg of magnesium, which is slightly more than the recommended RDA of 320 mg. So there shouldn’t be any reason that you have hardly any magnesium – I know you mention that you have been tested but it seems that there are underlying health issues as both of these are not typical.

    With regards to your question on the importance of magnesium: magnesium is very important. Magnesium is crucial to your overall health as it is essential for hundreds of biochemical reactions in the body and also plays a major role in supporting your bone health. Here are some articles on the importance and roles that magnesium plays: , ,

    If you need any more information, please let me know!

    – Monica @ AlgaeCal

  5. Karin

    March 12, 2023 , 2:30 pm

    from personal experience, I wonder if some of us actually need more magnesium. I find that if I don’t take 800-1000 mg of magnesium, I get a horrible case of restless leg syndrome. If I eat sugar (which is rare) I need even more.

  6. Chelsea Dugas

    March 13, 2023 , 2:00 pm

    Good point Karin. Some people do need more magnesium! We have this Magnesium-Rich Foods List if it helps! 🙂

    – Chelsea @ AlgaeCal

  7. Phyllis

    December 15, 2014 , 12:06 pm

    Just because your PTH was normal, doesn’t mean you don’t have parathyroid disease. I had high blood calcium levels for several years with normal PTH, but had a tumor on one parathyroid gland. I was finally diagnosed after going to and calling Dr. Norman’s office in Tampa, Fla. I suggest you check out the website.

  8. Anne

    October 14, 2018 , 8:41 pm

    To Tisha Rose: I also had a parathyroid tumor successfully removed at Norman Parathyroid Center. Go to their website to educate yourself – Seriously, if blood calcium is 10.0or above are you are over 40 yrs old, you likely have a tumor, regardless of your parathyroid hormone test! You are never too old to feel better!


    November 25, 2022 , 9:28 am


  10. Brianne AlgaeCal

    November 27, 2022 , 10:25 am

    Hello Sal,

    Most B1 (Thiamine) supplements on the market are water soluble. Sulbutiamine however is fat soluble. We unfortunately do not carry B vitamins, so check out your local health food store to see if they carry this! 🙂

    I hope this helps Sal!

    Brianne @ AlgaeCal

  11. Karen Woodard

    February 25, 2023 , 7:23 am

    Do you sell these vitamins…?Do they come in a pack or what?I am still having trouble digesting Algae Cal Plus.My pharmacist said to take B6 with it. Any comments…

  12. Chelsea Dugas

    February 28, 2023 , 6:41 am

    Thanks for reaching out Karen, and sorry to hear you are still struggling with digesting AlgaeCal Plus. Vitamins K and D are both contained within AlgaeCal Plus, but not vitamins A or E. The article is simply geared toward providing additional information and helping people understand their body’s daily nutritional requirements, be it through food or additional supplementation.

    Your doctor is definitely right about vitamin B6 – we normally recommend it in the form of P5P (activated B6). It’s relatively inexpensive and can be found in most health food stores and online! If you’d like more information and personalized support with this, please give our friendly Bone Health Consultants a call, 7 days a week, at 1-800-820-0184 or email [email protected]. They’ll be more than happy to help! 🙂

    – Chelsea @ AlgaeCal

  13. Toffee Real

    February 25, 2023 , 4:58 pm

    does AlgaeCal Plus contain these 4 vitamins?

  14. Joanie Power

    February 25, 2023 , 5:14 pm

    I am always very interested to read your articles however it is somewhat frustrating as I cant access AlgaeCal in Australia.
    The current article is extremely interesting to read. I have oesteoporosis and take a supplement called AdvaCal which is a BioCeuticals product. Are you able to comment on the ingredients and perhaps recommend areas where another supplement needs to be taken separately.
    Thank you for the support you give through your articles.

  15. Chelsea Dugas

    February 28, 2023 , 6:54 am

    Thanks for reaching out, Joanie! Unfortunately, we cannot comment on other products. That said, we do ship regularly to Australia! You can place an order directly on our website HERE, or you can contact our Bone Health Consultants at +1-510-564-7192 (International, long-distance charges apply) or by email at [email protected] for more information and personalized support. I hope this helps! 🙂

    – Chelsea @ AlgaeCal

  16. Heidi Dukes

    March 2, 2023 , 6:26 am

    Could I have hard copy of newsletter sent to my friend who’s 80?

  17. Yoori AlgaeCal

    March 2, 2023 , 5:42 pm

    Hi Heidi,

    We are truly sorry that the paper copy of our Bone Health Companion is only available for our community members at this time. That said, I’ve gone ahead and emailed you the PDF file which you are more than welcome to share with your friend :).

    I hope this helps!

    – Yoori @ AlgaeCal

  18. Cheryl M Nakagawa

    October 4, 2023 , 11:14 am

    If we start taking this new supplement, will it compound on the Vitamin D & K2 already in AlgaeCal Plus?

  19. Yoori AlgaeCal

    October 5, 2023 , 2:41 pm

    Thank you for reaching out, Cheryl! If you start taking these vitamins, it will add additional benefits to the vitamin D3 and K2 already in AlgaeCal Plus. While for some people, the 1600IU of vitamin D3 and 100mcg of vitamin K2 will be sufficient to reach the optimal level, others may need an extra depending on their vitamin D blood level. There is some debate about the optimal level of vitamin D in the blood, and we recommend working with your doctor to find the optimal dose of each vitamin that’s the best fit for you. I hope this helps! 🙂

    – Yoori

  20. Joan Milner

    October 4, 2023 , 4:24 pm

    Thanks, but I wish you’re author had included food sources for each vitamin. Joan

  21. Yoori AlgaeCal

    October 5, 2023 , 2:31 pm

    Great point, Joan! I will be happy to pass this feedback onto our team :). For your reference, I have listed a few sources of these four vitamins down below for your convenience:

    Vitamin D: Sunshine
    Vitamin K2: Fermented vegetables (natto, sauerkraut), yogurt, cheese
    Vitamin A: Carrots, broccoli, lettuce, tomatoes
    Vitamin E: Avocado, kiwi, olive oil, sunflower oil

    I hope this helps!

    – Yoori

  22. Elaine Petersen

    November 8, 2023 , 11:31 am

    In September 2023 my Vitamin D 25-Hydroxy result was 77.2, Units ng/mL, Normal Range 30.0-100.0.

    I do not take a separate Vitamin D. I get all my Vitamin D from supplements that contain Vitamin D. Will my Vitamin D level be too high if I take Vitamin D3?

    I purchased 3 bottles of Vitamin D3 but have not taken any yet because of my concern of taking too much Vitamin D.

    Will taking D3 dangerously increase my Vitamin D level?

    How do I take D3 without affecting my Vitamin D level?

  23. Yoori AlgaeCal

    November 9, 2023 , 5:03 pm

    Thank you for reaching out, Elaine! The amount of vitamin D supplementation a person needs depends on the Vitamin D levels in their bloodstream. There is some debate about the optimal level of vitamin D in the blood. The Endocrine Society suggests maintaining levels above 30 ng/mL, some researchers suggest maintaining level preferably at 40–60 ng/mL (study HERE) to achieve the optimal overall health benefits of vitamin D and another study HERE indicates that levels from 60-80 ng/ml may be needed to reduce cancer risk. Ultimately, your optimal levels will depend on your current health status and health goals.

    We recommend discussing the optimal dose of vitamin D with your doctor as we are not medical professionals :).

    – Yoori

This article features advice from our industry experts to give you the best possible info through cutting-edge research.

Lara Pizzorno
MDiv, MA, LMT - Best-selling author of Healthy Bones Healthy You! and Your Bones; Editor of Longevity Medicine Review, and Senior Medical Editor for Integrative Medicine Advisors.,
Dr. Liz Lipski
PhD, CNS, FACN, IFMP, BCHN, LDN - Professor and Director of Academic Development, Nutrition programs in Clinical Nutrition at Maryland University of Integrative Health.,
Dr. Loren Fishman
MD, B.Phil.,(oxon.) - Medical Director of Manhattan Physical Medicine & Rehabilitation and Founder of the Yoga Injury Prevention Website.,
Prof. Didier Hans
PHD, MBA - Head of Research & Development Center of Bone Diseases, Lausanne University Hospital CHUV, Switzerland,