Fat-soluble Vitamins


Last week, we looked at fats as part of "The Basics" series. Continuing that conversation, today we're going to be looking at fat-soluble vitamins: Vitamin A, Vitamin D. Vitamin E, and Vitamin K. We're going to be looking at what each of these vitamins is important for, where to find them in our diet, and if supplementation is necessary- what forms to look for in your supplements. Let's dive in! 

What are the fat-soluble vitamins?

Vitamins are the essential nutrients that our bodies need in small amounts (i.e. micronutrients) to perform various tasks. There are two classifications of vitamins: water-soluble and fat-soluble. Fat-soluble vitamins are so cool! They are the only vitamins that are stored in our body (thank you liver and adipose tissue), and we need fat present in our foods in order to absorb these vitamins. Since our bodies can store fat-soluble vitamins, we can run the risk of toxicity. Generally, this will not be an issue unless you are using mega-dose supplementation. If this is the case, seek out professional oversight to make sure you do not make yourself sick. 

A look at each vitamin:

Vitamin A

When we talk about Vitamin A, we are really referring to a wide range of fat-soluble nutrients such as retinol and beta-carotene. The bioactive form of Vitamin A is retinoic acid (RA), which acts as a nutrigenomic "hormone" that can alter gene expression and influence many physiological processes in the body. 

Vitamin A is best known for it's influence on vision, but it also supports your reproductive, digestive, urinary, and immune systems. Vitamin A is also essential for healthy bones, skin, and eyes. 

The recommended daily allowance (RDA) for Vitamin A is 900 micrograms for adult men and 700 micrograms for adult women. Fantastic food sources of Vitamin A include turkey giblets, beef liver, carrots, spinach, sweet potatoes, pumpkin, collard greens, kale, winter squash, turnip greens, and sweet red peppers. Remember- there are several forms of Vitamin A, so eating a diet with a variety of sources will be the healthiest for you. 

Supplementing Vitamin A: 

The major forms of supplemental Vitamin A include retinol esters and beta-carotene. Retinol forms are mainly found in the animal sources of Vitamin A, see above, and generally, beta-carotene is found in the plant sources. The majority of Vitamin A, natural or supplemental, comes in the form of beta-carotene. After ingestion, beta-carotene is metabolized in the small intestine and reduced to retinol. Natural forms of beta-carotene contain several cis-isomers, while the synthetic form (found in fortified foods, many supplements, etc) only contains a single trans-isomer. If you are not regularly ingesting different types of beta-carotene (or Vitamin A in general) you will become unbalanced. 

If you are concerned about getting adequate levels of all kinds of Vitamin A, but can't bring yourself to cook up some beef liver or turkey giblets- there is good news! There is an alge species, Dunaliella, which is composed of a nearly 50/50 balance of cis and trans Vitamin A isomers. This alge has begun being used in some supplements, often called a "mixed carotenoid". This is the supplementation form that I recommend to my clients, if they are lacking in dietary Vitamin A.  


Vitamin D

As I write this post, it is cold, rainy, and grey in England. So, basically on par with our usual weather. It is also January. Did you know that living above the 37th parallel means that from roughly October through March, the sun's rays are not strong enough to deliver any Vitamin D to our bodies? Even on the rare sunny day, we are gleaning no benefit from the sun! That is why many people living in this part of the world are at least mildly deficient in Vitamin D. 


IF you feel you need to supplement any fat-soluble vitamin- please first seek out a qualified nutritionist to go over your dietary intake, lifestyle factors, and other components that will affect your intake and utilization. It is important to get a healthy balance with fat-soluble vitamins, as they do accumulate in the body and can cause toxicity. If needed, your nutritionist will suggest a form of supplementation that is highly bioavailable and in a good amount for you.

Vitamin D helps our bodies build and maintain strong bones and teeth. It is also essential to the functioning of our nerves and muscles. More and more research is emerging linking mental health issues such as depression and anxiety to deficiencies in Vitamin D. Additionally, it is crucial to our immune system, and adequate levels are linked to a lower risk of multiple sclerosis, heart disease, and fibromyalgia. 

Many lifestyle and environmental factors can affect our ability to absorb and maintain adequate levels of Vitamin D, including pollution, spending excessive time indoors, and living in larger cities (as buildings tend to block sunlight). When we are deficient in Vitamin D, we often feel fatigued and achey, and have a general sense of just not feeling well. Being overweight or obese increases our bodies' need for Vitamin D. 

There is a lot of controversy surrounding how much Vitamin D we really need. The best way to discover what you need is by performing a simple blood test to check your levels of this important vitamin. Normal blood serum markers range from 50-100 micrograms per deciliter (mg/dL). If you are below this range, you will need to increase your intake of Vitamin D rich foods or supplement. The recommended IU's (international units) of Vitamin D for adults/day is far too low to change your blood serum levels. Currently the RDA is set at 600IU for adults. Depending on your blood serum levels, a dose of 1,000-2,000 will adequately maintain a healthy level and a dose of 5,000 or more may be needed to bring up a deficient level. Blood levels should be checked every 3 months if you are trying to bring up serum levels and every 6-12 months to maintain. Do not begin or alter a supplementation program without the supervision of a qualified nutritionist or medical professional. 

The only 100% natural form of Vitamin D for humans comes from direct sunlight or from the consumption of oily fish such as mackerel or salmon. Other food sources include egg yolks and shrimp. Milk, cereals, and yogurt can all be found fortified, but are often using a sub-par source of the vitamin. The most common supplemental form of Vitamin D is D3. Vitamin D3 is created from the conversion of cholesterol derivatives found in sheep wool lanolin. A superior form of supplementation comes from sustainably caught organic cod liver oil. Cod liver oil is a natural fat that has many other healthful properties. Toxicity with Vitamin D supplementation is rare, but possible, with long term mega doses. 

Vitamin E

Vitamin E protects your body organs, tissues, and skin from the damaging effects of free radicals and contributes to their overall health and functioning. Free radicals are formed when your body tries to deal with harmful environmental toxins from UV light radiation, air pollution, tobacco smoke, etc. Like Vitamin A, E is a collection of fat-soluble compounds with distinct antioxidant activities. Naturally occurring, there are 8 chemical forms of Vitamin E, however only one, alpha-tocopherol, is used by our bodies, the others are excreted. Thanks to its antioxidant properties, Vitamin E may prevent or delay chronic diseases that are associated with free radicals. 

Food sources of Vitamin E include: wheat germ oil, sunflower seeds, almonds, hazelnuts, spinach, broccoli, mango, and raw tomatoes. Cooking can help increase the bioavailability of Vitamin E in spinach, broccoli, and nuts. 

A word of caution: Vitamin E is also abundant in many vegetable oils, such as corn oil, soybean oil, safflower oil, and sunflower oil. While I encourage you to get as many nutrients as possible through your diet, I do not recommend consumption of these highly processed and refined oils. Consumption of these increases your bodily inflammation and contributes to many chronic diseases. 

Deficiency of Vitamin E is very rare- most often occurring in premature infants with very low birth weight, but almost never occurring in healthy adults- even when they do not consume many Vitamin E containing foods. It is generally not necessary to supplement with Vitamin E. 

Vitamin K

Derived from the German word koagulation, Vitamin K is named for its first known function- blood coagulation. Vitamin K is a coenzyme required for the synthesis of the proteins involved in hemostasis (blood clotting) and bone metabolism, as well as a myriad of other physiological functions. 

Recommended intakes of Vitamin K for adults is 120mcg and 90mcg for adult men and women, respectively. Food sources of Vitamin K include green leafy vegetables (kale, swiss chard, spinach), vegetable oils (caution!), and some fruits. Our daily needs for Vitamin K are very small, and just 1/2 cup of turnip greens boiled will provide nearly 700% of our needed intake. 

Excessive bleeding or hemorrhage are the classic signs of Vitamin K deficiency, however, these symptoms are relatively extreme. Bone mineralization (resulting in osteoporosis) is another sign of Vitamin K deficiency. Due to these extreme markers, it is wise to simply include modest amounts of Vitamin K rich foods into the diet regularly. There is currently no upper limit for Vitamin K intake. 

Individuals with fat malabsorption issues

Fat malabsorption is caused by your intestines' inability to absorb nutrients from your body. If you have impaired fat absorption, you may also have difficult absorbing and utilizing fat-soluble vitamins! Fat malabsorption tends to be an issue with individuals suffering from inflammatory bowel disease, leaky gut syndrome, those who have had their gallbladder removed, and those on certain medications. If you suffer from any of these, or any other malabsorption, it is imperative that you speak with a qualified nutritionist or healthcare professional to address any deficiencies and work to correct your malabsorption issues.


Did I give you all the information you could possibly want on fat-soluble vitamins? Do you have any questions regarding these important micronutrients? Is there something you'd like to see me cover in the future? Leave a comment and let me know! I love hearing from my readers!