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Fat-soluble vitamins are vitamins A, D, E, and K. They are present in foods containing fats. The body absorbs these vitamins as it does dietary fats. They do not dissolve in water.
Vitamins help the body function effectively. There are two types: water-soluble and fat-soluble vitamins. The water-soluble vitamins are vitamins B and C.
Most vitamins come from food, but sunshine contributes to vitamin D. Some people need or choose to take supplements that provide extra vitamins.
The body absorbs fat-soluble vitamins best when a person eats them with higher-fat foods.
This article looks at the types, functions, and sources of fat-soluble vitamins, and what can happen if a person has too much or too little.
Vitamin A helps maintain healthy vision. Without vitamin A, a person could experience vision problems and possibly vision loss.
Vitamin A is not a single vitamin but a collection of compounds known as retinoids. Retinoids occur naturally in the human body, and they are present in some dietary sources.
Some foods provide retinols, which the body can use directly as vitamin A. Others provide provitamin A, compounds that the body converts into vitamin A.
Vitamin A supports several functions throughout the body, including:
- the immune system
People can obtain vitamin A through dietary sources.
Animal sources provide preformed vitamin A, or retinols. This type is ready for the body to use.
For this reason, lists of ingredients often show vitamin A content as “vitamin A RAE.” RAE means “retinol activity equivalents.”
Animal sources of vitamin A include:
- fish liver oil
- beef liver
- cheese, milk, and other dairy products
- Sources of beta carotene include:
- sweet potato
- kale, spinach, and other green, leafy vegetables
- black-eyed peas
- fortified breakfast cereals
Find out more here about dietary sources of vitamin A.
Nutritionists measure some vitamins in two ways:
- micrograms (mcg) RAE
- international units (IU)
Food packages usually show the amounts in IU. A diet that contains 900 mcg RAE of vitamin A, which is the recommended intake for males over 14 years of age, would provide around 3,000–36,000 IU of vitamin A, according to the Office of Dietary Supplements (ODS).
Anyone who has concerns about their vitamin A intake should seek advice from a health professional, who will help them understand these measures.
The recommended intake of vitamin A varies by age and sex.
The 2015–2020 Dietary Guidelines for Americans recommend consuming the following amounts each day. Amounts are in mcg RAE.
|Age (years)||1–3||4–8||9–13||14 and over|
Vitamin A deficiency is rare in the United States, but it can affect a person who:
- follows a plant-based diet
- has cystic fibrosis
A long-term deficiency can lead to a loss of night vision and possibly a total loss of vision.
Too much vitamin A can be toxic.
It can affect:
- people who take vitamin A supplements
- those with a high intake of fish liver oil
- people who take medications that contain retinoids, such as acitretin (Soriatane), a treatment for psoriasis
During pregnancy, high levels of vitamin A can harm a growing fetus.
Symptoms of an overdose include:
In severe cases, coma and death can result.
Vitamin A supplements are available for purchase online. However, people should speak to a doctor before taking these or other supplements.
The time a person takes a vitamin can affect its impact. Find out more here about when to take different vitamins.
People obtain vitamin D:
- naturally through exposure to sunlight or in the diet
- through fortified foods
- as supplements
The body obtains the compounds it needs to make vitamin D from food. It also produces vitamin D when ultraviolet (UV) light meets the skin.
Vitamin D is not a single substance but a group of compounds collectively known as calciferol.
The body absorbs calciferol into the bloodstream and then converts it to calcitriol.
Two types occur naturally:
- vitamin D-3, found in animal fats
- vitamin D-2, found in plants, such as mushrooms
Vitamin D has two main roles in the body:
- It maintains bone health.
- It supports the immune system.
A person can obtain some vitamin D from the sun, but most people will also need to use other sources, too. The main alternative is food.
Dietary sources include:
- oily fish and fish oils
- fortified dairy products, plant-based milks, and cereals
- beef liver
How can you get more vitamin D from the sun? Click here to find out.
Experts measure vitamin D in international units (IU).
Current guidelines recommend that people of all ages intake of 600 IU of vitamin D daily. This is hard to measure, however, as it is not easy for a person to know how much vitamin D they obtain from sunlight.
A vitamin D deficiency can affect:
- older adults and children who do not spend much time out of doors
- people with darker skin
- some people with chronic health conditions
- those who live far from the Equator, where winter days are short
- those with obesity
The main effects of vitamin D deficiency include:
- osteoporosis, or loss of bone mass
- osteomalacia, when bones become soft
- rickets, when a child’s bones do not develop as they should
- increased risk of infection and autoimmunity
It is rare for a person to have too much vitamin D, but using supplements could trigger this.
Having too much vitamin D could lead to high levels of calcium in the blood.
This can lead to:
- low appetite and weight loss
- a buildup of calcium in tissues and blood vessels
- heart or kidney damage
- high blood pressure
Vitamin D supplements are available for purchase in pharmacies and online. A person should speak to their doctor before using these supplements, however.
Vitamin E is an antioxidant that can help the body destroy free radicals. Free radicals are unstable atoms that can cause oxidative stress. Oxidative stress can lead to cell damage, and this can result in cancer and other diseases. Vitamin E may help protect the body from a range of health issues.
There are eight forms of vitamin E, but only alpha-tocopherol meets humans’ needs, according to the ODS.
Some reasons why the body needs vitamin E are:
- as an antioxidant
- to boost the immune system
- to dilate blood vessels and help prevent clotting
Good sources of vitamin E include:
- wheat germ oil
- sunflower seeds and oil
- almonds, hazelnuts, and peanuts
- spinach and broccoli
- kiwi fruit and mango
Which foods are good sources of vitamin E? Find out here.
Current guidelines recommend people consume the following amounts of vitamin E. Experts measure vitamin E intake in milligrams (mg) AT, but packaging currently uses international units (IU).
|Age (years)||1–3||4–8||9–13||14 and over|
|Female||6 mg (9IU)||7 mg (10.4 IU)||11 mg (16.4 IU)||15 mg (22.4 IU)|
|Male||6 mg (9IU)||7 mg (10.4 IU)||11 mg (16.4 IU)||15 mg (22.4 IU)|
The ODS note that, during breastfeeding, a female should consume 19 mg (28.4 IU) each day.
Vitamin E deficiency is rare, but it can affect people with Crohn’s disease or cystic fibrosis. These conditions affect the liver’s ability to absorb vitamin E.
A deficiency can result in:
- nerve and muscle damage that affects movement and coordination
- vision problems
- a weakened immune system
As vitamin E is an antioxidant, a long-term deficiency could increase the overall risk of various diseases.
Click here to find out how to recognize a vitamin E deficiency.
Obtaining vitamin E through natural sources is unlikely to lead to an overdose, although supplement use can increase this risk.
People who use blood-thinning medication, such as warfarin (Coumadin) should ask their doctor before taking vitamin E supplements, as these may interfere with blood clotting.
Vitamin E supplements are available for purchase in pharmacies and online.
Vitamin K helps the body form blood clots. Blood clotting is essential to prevent excessive bleeding.
There are several types of vitamin K.
The two most common groups are:
- 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.
Apart from blood clotting, vitamin K may also:
- lower the risk of heart disease
- enhance bone health
- reduce the buildup of calcium in the blood
Food sources of vitamin K-1 and K-2 include:
- egg yolks
Learn about 40 foods that provide vitamin K.
Experts do not have enough evidence to recommend a specific intake of vitamin K suitable to meet the needs of 97-98% of healthy individuals.
Instead, they recommend an adequate intake (AI), an amount assumed to provide nutritional adequacy, as follows:
|Age (years)||1–3||4–8||9–13||14–18||19 and over|
The body is not able to store as much vitamin K as it does vitamin A or D. This means a person needs a regular intake of vitamin K, and there is a higher chance of a deficiency.
A vitamin K deficiency may result in:
- excess bleeding
- lower bone density, in the long term
Learn more about a vitamin K deficiency here.
Taking high quantities of vitamin K does not appear to lead to adverse effects. However, it can interfere with the use of blood-thinning medications, such as warfarin (Coumadin).
Vitamin K supplements are available for purchase in pharmacies and online. However, people should speak to a doctor before using them, especially if they use blood thinners or have a condition that affects blood clotting.
Fat-soluble vitamins are essential for overall health. Most people can obtain enough of each vitamin from a varied and healthful diet. Anyone who has concerns about their vitamin intake should speak to a doctor.
In some cases, a doctor may recommend taking supplements.
Is it really worth taking supplements?