What's the Difference Between Fat- and Water-Soluble Vitamins?

  • Author:
    Betty Kovacs Harbolic, MS, RD

    Betty is a Registered Dietitian who earned her B.S. degree in Food and Nutrition from Marymount College of Fordham University and her M.S. degree in Clinical Nutrition from New York University. She is the Co-Director and Director of nutrition for the New York Obesity Research Center Weight Loss Program.

  • Medical Editor: William C. Shiel Jr., MD, FACP, FACR
    William C. Shiel Jr., MD, FACP, FACR

    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Ask the experts

What are the characteristics of fat- and water-soluble vitamins?

Doctor's response

Vitamins are one of the six essential nutrients that our bodies need to function. These essential nutrients are broken up into two groups based on the amount that is needed:

  1. Macronutrients: protein, carbohydrates, fat, and water
  2. Micronutrients: vitamins and minerals

While vitamins are needed in small quantities, they perform huge functions in our bodies. They are needed for normal function, growth and maintenance of body tissues, and to regulate and support chemical reactions in the body. In order to be classified as a vitamin, absence of the nutrient from the diet must result in a disease that can be cured by the timely replacement of that nutrient. For this reason, the absence of any vitamin from your diet would result in a deficiency that would only be corrected by ingesting that vitamin.

Vitamins fall into two categories: fat soluble and water soluble. The type of solubility has to do with how the vitamins are absorbed and transported, whether or not they can be stored in the body, and how easily they are lost from the body. The fat-soluble vitamins are A, D, E, and K. Being fat soluble means that they are absorbed in the lymph, are transported in the blood with carrier proteins, and they can be stored in the liver and fatty tissues. The fact that these vitamins can be stored means that they can also build up to toxic levels when consumed in excessive amounts. It is very important to stick to the guidelines on how much is necessary and how much is dangerous.

The water-soluble vitamins are B and C. The B vitamins include thiamin, riboflavin, niacin, folate, pyridoxine, and B12. The water-soluble vitamins are easily dissolved and can be excreted in the urine. This does not mean that you can take these in unlimited quantities. There can be problems with excessive amounts, so upper limits have also been set for the water-soluble vitamins. You can find detailed information on sources, requirements, functions, and upper limit levels for all vitamins at the USDA Food and Nutrition Information Center.

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Medically reviewed by Robert Bargar, MD; Board Certification in Public Health & General Preventive Medicine

REFERENCE:

"Vitamin supplementation in disease prevention"
UpToDate.com

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Last Editorial Review: 7/12/2017

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