The different types of fat-soluble vitamins — and how to get enough of them
- Fat-soluble vitamins include vitamins A, E, D, and K.
- The body requires fat in order to absorb fat-soluble vitamins.
- Fat-soluble vitamins can be stored in the liver and fatty tissues for long periods of time, making it easier to develop vitamin toxicity.
- This article was medically reviewed by Samantha Cassetty, MS, RD, nutrition and wellness expert with a private practice based in New York City.
All vitamins are either fat-soluble or water-soluble. The difference between them is how they are absorbed and stored in the body.
Both fat and water-soluble vitamins are absorbed during digestion. Afterward, any excess fat-soluble vitamins are stored in the liver and fatty tissues whereas excess water-soluble vitamins are flushed out of the body.
This difference affects how much of each vitamin type you need, how often you need it, and the risks of consuming too much. There are four types of fat-soluble vitamins: A, D, E, and K.
Here's everything you need to know about fat-soluble vitamins from where to find them and their role in the body.
What are fat-soluble vitamins?
Fat-soluble vitamins are those that, fittingly, dissolve in fat. In order to be absorbed, they require fat — usually from food in the stomach — to be present. If they aren't absorbed during digestion, any excess is stored in the liver and fatty tissues for later use with functions such as vision and controlling blood clots.
In comparison, water-soluble vitamins — like vitamins C, B6, and B12 — can be absorbed on an empty stomach and do not require any fat present, says Ashley Reaver, MS, RD, CSSD, a dietetic lecturer at the University of California, Berkeley. Any excess exits through the urine.
Thanks to their ability to be preserved in tissue, fat-soluble vitamins don't need to be consumed as often as water-soluble vitamins.
But, because fat-soluble vitamins can not be excreted through the urine, they have the potential to build up in the body and even reach toxic amounts. However, Nicole DeMasi Malcher, MS, RDN, CDCES, a registered dietitian-nutritionist with her own virtual private practice, says toxicity rarely happens due to diet alone and is often a result of excessive supplement use.
Consumed in proper quantities, fat-soluble vitamins are critical for "normal function, growth, and maintenance of tissues, " says Malcher. They also function as antioxidants which means they support the immune system and prevent premature aging of cells.
Each fat-soluble vitamin plays a distinct role in the health and functioning of the body. Here's a break down for each fat-soluble vitamin and its unique health benefits:
Vitamin A
The primary role of vitamin A is an important process called cell differentiation. This process specializes cells for a specific function in the body.
"Cell differentiation is what allows cells in the eyes to transfer images to the brain and cells in the intestines to absorb nutrients," says Reaver. "It is incredibly important for a growing fetus during pregnancy, but remains critical throughout the lifespan, in particular for eye health."
Vitamin A is available in various fruits and vegetables, including carrots, pumpkin, sweet potatoes, spinach, kale, and tomatoes. It's easy to spot vitamin A-rich foods thanks to carotene — a precursor to vitamin A found in foods like carrots that exude a deep orange color. Animal products such as butter, cheese, and egg yolk are another great source of the nutrient.
Read more about how to recognize the symptoms of vitamin A deficiency or toxicity.
Vitamin D
Vitamin D helps regulate calcium absorption from the intestine. Calcium helps with muscle contraction, blood pressure management, and maintaining proper bone density.
When the body doesn't have enough vitamin D, it must remove calcium from the bone in order to maintain its necessary functions. This can cause conditions such as osteoporosis and rickets.
While the nutrient is present in some foods such as fatty fish and mushrooms, vitamin D is mostly produced by our skin when in the sun. It can also be taken in supplement format, says Malcher.
Read more about the benefits of vitamin D and symptoms of vitamin D toxicity.
Vitamin E
Vitamin E is an antioxidant critical in protecting the body from free radicals.
Free radicals are unstable molecules that can come from outside sources — like cigarette smoke or pollution — or as a natural byproduct of the body's metabolic process.
They can potentially damage other cells in your body, which can increase the risk of developing cancer and other serious diseases. Getting enough vitamin E can help limit or prevent this severe damage.
Vitamin E also helps with the expansion of blood vessels, preventing harmful blood clots that could lead to heart attacks and strokes.
Vitamin E is abundant in sunflower seeds, nuts, and vegetable oils. Eating these foods is the most effective way to maintain your vitamin E levels.
Vitamin K
There are two main types of vitamin K: K1 and K2.
K1 is found in plant-based sources, while K2 is available in animal products. Both forms of vitamin K "aid in blood clotting, bone health, cardiovascular health, and several other functions in the body," says Malcher.
While most people do not need to worry about their vitamin K intake, babies are particularly vulnerable to a deficiency because they are born with low levels of vitamin K. That's why physicians recommend giving newborns a shot of vitamin K soon after birth.
Vitamin K1 is available in vegetables such as parsley, kale, spinach, and brussels sprouts, while K2 is in egg yolks, fermented soybeans, and beef.
Read more about the health benefits of vitamin K.
Takeaways
There are four fat-soluble vitamins: A, D, E, and K. They each require fat to be present in order to be absorbed by the body.
The body stores fat-soluble vitamins in the liver and fatty tissues, making them more likely to build up to toxic levels than water-soluble vitamins.
Vitamins A, E, and K are widely available in food, while vitamin D is mostly obtained from sunlight exposure.