Water-soluble vitamins dissolve easily in water. Because of this, they are easily broken down and excreted by the body and are not stored for future use. You need to constantly replenish your body's supplies of water-soluble vitamins like B-complex vitamins and vitamin C in order to have them available for use. Excess water-soluble vitamins you take in are generally eliminated or excreted in your urine.
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Water-Soluble and Fat-Soluble
Different vitamins play different roles in helping you to maintain your health. They are categorized according to what causes them to break down -- vitamins are either water-soluble, or broken down by water; or fat-soluble, or broken down in fat. Because water-soluble vitamins are so easily broken down, your body cannot store them over periods of time and excretes them through your urine. On the other hand, fat-soluble vitamins, which must dissolve in fat before they can be absorbed into the bloodstream. They are stored in your liver and therefore are not needed on a daily basis.
Because water-soluble vitamins are easily broken down, they also can be easily eliminated while you are storing or preparing foods. Therefore, store fresh fruits and vegetables as well as dairy and grains properly. Colorado State University recommends produce be refrigerated and grains and dairy be kept away from strong light to preserve their vitamin content.
B-complex vitamins tend to be found in a variety of foods, especially animal foods such as meat and dairy products and enriched grain products such as breads and cereals. Used by the body to metabolize foods, they are crucial for processes such as red blood cell formation and nerve cell repair. B-complex vitamins also contribute to your skin's ability to protect you and the nervous system's general ability to function. Since B-complex vitamins are so important to your body functions and cannot be stored, it is important that you take in adequate vitamin B from foods. Vitamin B your body does not use is excreted through your urine.
Vitamin C, which is abundant in citrus fruits such as pineapples and oranges, helps your body in the formation of connective tissue and bone, supports the immune systems, aids the process of healing injuries and helps your body to absorb iron. Vitamin C also works with vitamin E to act as an antioxidant, destroying harmful free radicals. Like B-complex vitamins, vitamin C must be taken in by your body regularly because you are unable to make or store it yourself. What you cannot use is excreted through urine rather than stored in the liver.
Water-Soluble Vitamin Research
Much of the scientific research involving the excretion of water-soluble vitamins involves whether measurements of the amount of vitamins excreted in the urine is an accurate reflection of the person's diet. One such study, published in the "Journal of Nutrition Science and Vitaminology" in August of 2010, sought to find how fasting would impact the urinary excretion of water-soluble vitamins. Researchers found that the amount of certain vitamins in the urine went down when study participants fasted, leading them to hypothesize that the vitamins were instead being retained by the body to support its nutritional needs.
Other similar studies have produced results that are fairly consistent; showing that people who consume higher levels of water-soluble vitamins tend to excrete larger amounts in their urine each day. In a 2008 study in the "Journal of Nutrition Science and Vitaminology," researchers suggest that measuring levels of water-soluble vitamins in the urine is a fairly good way to assess overall vitamin intake.