What’s a fat-soluble vitamin?
Fat-soluble vitamins are a subclass of vitamins. In order to be digested in the human body, fat-soluble vitamins require dietary fats, oils, or lipids. These include cooking oils, nuts, fish, meat, or avocados, for example. You may see these vitamin supplements made with “carrier” oils to boost availability.
If not consumed with fats, fat-soluble vitamins can’t be completely absorbed and used in the body. People who don’t eat enough dietary fats are more vulnerable to fat-soluble vitamin deficiencies. So are people who have problems absorbing fats.
Luckily, fat-soluble vitamins tend to naturally occur in food sources that contain fats. If you follow a balanced and varied diet, deficiencies are rare.
Fat-soluble vs. water-soluble
The other subclass of vitamins is known as water-soluble vitamins. These are absorbed more quickly and easily, since most foods naturally hold some water. They’re also passed and lost very quickly through urine output.
For this reason, intake needs for water-soluble vitamins are much higher. Because they’re so easily removed from the body, there is less risk of overdosing on them. Water-soluble vitamins are not stored in the body and need to be taken in every day.
Fat-soluble vitamins, on the other hand, may pose a risk for toxicity, or a buildup of excess vitamins. Fortunately, you don’t need high amounts to function, and your body stores theses vitamins for later use. It’s unlikely you’d ever overdose on vitamins eating them in foods.
More care is needed with supplements. The Food and Drug Administration doesn’t monitor the quality, strength, or purity of supplements. Purchase them from a reliable source, and don’t take more than the recommended allowance without discussing with a doctor. If you follow supplement dosage directions and eat well, you shouldn’t be concerned about overdosing.
Which vitamins are fat-soluble?
Vitamins A, D, E, and K are fat-soluble. B vitamins and vitamin C, on the other hand, are water-soluble.
Vitamin A is found in many yellow-colored fruits and vegetables. Good sources include:
- sweet potatoes
- winter squash
- dark leafy-green vegetables
- fatty animal tissue, such as liver or fish
You need vitamin A for good vision, cellular function, proper skin function, and reproductive health. People who are deficient in vitamin A will experience symptoms like night blindness. Fertility issues in women may also occur. Vitamin A deficiency is rare, though it can happen in young children. It’s a bigger problem in developing countries, according to the World Health Organization.
Vitamin D is almost entirely found in animal products, including red meat, seafood, and poultry. Cod liver is especially vitamin D-rich. It can be found in some UV-exposed mushroom varieties. White button mushrooms and shiitakes are excellent examples.
Otherwise, vitamin D is added to foods like fortified cereals, orange juice, and milk. You also receive much of your required vitamin D from sun exposure.
You need vitamin D so your body can use calcium and phosphorous to mineralize your bones. When deficient, you’re more likely to experience bone loss, fractures, and autoimmunity. Some thyroid problems cause vitamin D deficiency. Rickets is an advanced disease resulting from deficiency, but it’s quite uncommon today.
This vitamin is found in small amounts in a wide variety of oil-containing plant foods. The best sources are:
- vegetable oils
- fruits and vegetables
- grains, such as oats
Vitamin E is required for neurological health, muscular health, blood function, and some visual function. Deficiencies are rare in developed countries. When they do happen, it’s usually due to low fat intake. Sometimes, it may be caused by a disorder interfering with fat absorption.
Signs of deficiency may include neurological dysfunction, muscular weakness, or mild hemolytic anemia.
Green leafy vegetables are very rich in vitamin K. Meat and animal products may contain it, but to a lesser extent. You need the vitamin for proper blood clotting, bone health, growth, and protein production.
Symptoms of deficiency may include hemorrhaging and difficulty forming blood clots. This is extremely rare and happens only in severe cases. These symptoms may be more likely in those who take anticoagulants or antibiotics. Antibiotics may cause deficiency because vitamin K is produced by microbes in the intestine.
Recommended daily allowance
The recommended daily allowance for fat-soluble vitamins is:
|Vitamin A||• 900 micrograms (3,000 international units, or IU) for men|
• 700 micrograms (2,300 IU) for women
• 3000 micrograms is the Tolerable Upper Intake Level (UL) for adults.
|Vitamin D||• 20 micrograms for adults|
• 100 micrograms is the UL for adults.
|Vitamin E||• 15 micrograms for adults|
• 1000 milligrams is the UL for adults.
|Vitamin K||• 120 micrograms for men|
• 90 micrograms for women
• No UL is known yet.
Colorado State gives more information on dosages for infants, children, or those pregnant or breastfeeding.
The bottom line
Deficiencies in fat-soluble vitamins are unlikely if you eat a rich and varied diet. Eating a variety of fruits, vegetables, nuts, and grains is especially important.
Your body stores these vitamins for later use in the skin and liver. Even if you don’t get your daily allowance all the time, you still avoid deficiency. If you have certain illnesses this may be a different matter. Talk to your doctor if you have concerns.
A need for these vitamins to be supplemented in the diet is rare. Still, your doctor may prescribe a supplement if you are deficient or have certain illnesses. You may also find these vitamins in typical daily supplements, such as vitamin A. If you’re pregnant, your doctor can help you determine how to address deficiencies. The retinol found in vitamin A can be harmful to an unborn baby if the mother takes higher than recommended doses, and retinol-based face creams are not recommended.
Remember: Fat-soluble vitamins don’t get discarded from the body as easily as water-soluble ones. Taking excess supplement doses over a long period of time may adversely affect your health.