Fat-Soluble vs. Water-Soluble Vitamins

How They Differ in Absorption and Storage in the Body

We take vitamins and supplements to bolster those we get from the foods we eat and the sunlight we are exposed to. They are absorbed into the body in different ways and excreted from the body at different rates. We can broadly classify them as being either water-soluble or fat-soluble.

Vitamins on a table
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Water-Soluble Vitamins

Water-soluble vitamins are those that are dissolved in water and readily absorbed into tissues for immediate use. Because they are not stored in the body, they need to be replenished regularly in our diet.

Any excess of water-soluble vitamins is quickly excreted in urine and will rarely accumulate to toxic levels. With that being said, certain types of water-soluble vitamin, such as vitamin C, can cause diarrhea if taken in excess.

The water-soluble vitamins include the B-complex group and vitamin C, each of which offers the following health benefits:

  • Vitamin B1 (thiamine) helps to release energy from foods and is important in maintaining nervous system function.
  • Vitamin B2 (riboflavin) helps promotes good vision and healthy skin and is also important in converting the amino acid tryptophan into niacin.
  • Vitamin B3 (niacin) aids in digestion, metabolism, and normal enzyme function as well as promoting healthy skin and nerves.
  • Vitamin B5 (pantothenic acid) aids in metabolism and the formation of hormones.
  • Vitamin B6 (pyridoxine) aids in protein metabolism and the production of red blood cell, insulin, and hemoglobin.
  • Vitamin B7 (biotin) helps release energy from carbohydrates and aids in the metabolism of fats, proteins, and carbohydrates from food.
  • Vitamin B9 (folate or folic acid) also aids in protein metabolism and red blood cell formation and may reduce the risk of neural tube birth defects.
  • Vitamin B12 (cobalamin) aids in the production of normal red blood cells as well as the maintenance of the nervous system.
  • Vitamin C (ascorbic acid) is central to iron absorption and collagen synthesis. It aids in wound healing and bone formation while improving overall immune function.

Fat-Soluble Vitamins

Fat-soluble vitamins are dissolved in fats. They are absorbed by fat globules that travel through the small intestines and distributed through the body in the bloodstream.

Unlike water-soluble vitamins, excess fat-soluble vitamins are stored in the liver and fatty (adipose) tissues for future use They are found most abundantly in high-fat foods and are better absorbed if eaten with fat.

Because fat-soluble vitamins are not readily excreted, they can accumulate to toxic levels if taken in excess. Where a well-balanced diet can't cause toxicity, overdosing on fat-soluble vitamin supplements can.

There are four types of fat-soluble vitamin, each of which offers different benefits:

  • Vitamin A is integral to bone formation, tooth formation, and vision. It contributes to immune and cellular function while keeping the intestines working properly.
  • Vitamin D aids in the development of teeth and bone by encouraging the absorption and metabolism of phosphorous and calcium.
  • Vitamin E is an antioxidant that helps fight infection and keeps red blood cells healthy.
  • Vitamin K is central to blood clotting and also keeps bones healthy.

Frequently Asked Questions

  • What happens if you take too much of a fat-soluble vitamin supplement?

    The symptoms and side effects of fat-soluble vitamin toxicity vary depending on the vitamin. They range from nausea and vomiting to slowed growth and birth defects.

  • How much vitamin A is safe to take?

    The daily tolerable upper intake level for vitamin A supplements according to age are:

    • Babies and children under 3: 300 micrograms (mcg)
    • Children 4 to 8: 900 mcg
    • Tweens 9 to 13: 1700 mcg
    • Teens 14 to 18: 2800 mcg
    • Adults 10 to 70 and older: 3000 mcg
  • How can I remember which vitamins are fat-soluble and which are water-soluble?

    The easiest way is to memorize the fat-soluble ones, as there are only four: vitamins A, D, E, and K. All others are water-soluble.

  • Why is it possible to overdose on fat-soluble vitamins but not water-soluble ones?

    Because water-soluble vitamins dissolve in water right away. Once the body has as much of one as it needs, the rest gets flushed out of the body by the kidneys. Excess fat-soluble vitamins, on the other hand, wind up stored in the liver, where they can build up to the point of causing damage.

  • Is it possible to get too much of any of the water-soluble vitamins?

    Yes. Several have upper limits for consumption, meaning that even though they aren't stored, they could cause problems if too much is circulating in the body. For example, a high level of vitamin B6 for an extended period of time is associated with nerve damage that cannot be reversed.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  3. Colorado State University. Fat-Soluble Vitamins A, D, E, and K—9.315.

  4. University of Michigan Health. Vitamins: Their functions and sources. Updated Dec 17, 2020.