What in Vitamins Makes My Urine Turn Yellow?

Multivitamins, B-complex vitamins and even heavily vitamin-fortified cereals will often cause your urine to turn a bright, seemingly unnatural shade of yellow. Although this might alarm you the first time it happens, it is an entirely normal response when you have ingested a high dose of riboflavin, also called vitamin B-2.

The urinary system aids the body in eliminating waste, including excess riboflavin. Credit: SomkiatFakmee/iStock/Getty Images

Function of Riboflavin in the Body

Together with other B vitamins, riboflavin helps the body release energy from carbohydrates, contributes to the metabolism of fat and is critical in the creation of red blood cells. In addition to these functions, there is some evidence to support the idea that riboflavin acts as an antioxidant, which may help prevent some forms of cardiovascular disease and cancer. At higher doses, vitamin B-2 has been used in some people to fight migraine headaches and possibly cataracts; however, more research is necessary to confirm these observations.

Recommended Dietary Allowance for Riboflavin

When looking at the nutrition label of most multivitamins or B-complex supplements, you might think that a person needs high amounts of riboflavin and other B vitamins. But, rather than the 25, 50 or 75 milligrams often found in these commercial products, a typical adult woman only needs 0.9 milligram per day, and a typical adult male only needs 1.1 milligrams per day. These small amounts are easily met with a well-balanced diet, and deficiencies are often only seen in people with malabsorption problems, which can occur in celiac disease, alcoholism and occasionally in the elderly. That said, people who are very physically active, such as laborers and athletes, may have an increased need for riboflavin, reports the Linus Pauling Institute.

Foods and Beverages That Supply Riboflavin

Dairy products are an excellent source of riboflavin. Credit: indigolotos/iStock/Getty Images

Riboflavin is present in a wide variety of foods. Dairy products including milk are some of the best sources of B-2. If you choose not to consume dairy or you cannot due to dairy allergy or intolerance, additional healthy sources of the vitamin include legumes, nuts, lean meats, green leafy vegetables, eggs and nuts. In the United States, many grain products, including flours, breads and cereals, are also fortified with riboflavin during the manufacturing process, which means that the vitamin is added to the food in higher doses than would normally be present.

Other Effects of Excess Riboflavin

Historically, scientists believed that riboflavin toxicity was rare because the excess is excreted via the urinary tract system -- thus, the bright yellow color of the urine. But some recent studies have suggested possible damage to the eyes, nerves and connective tissue if B-2 is taken in large doses. In addition, consult your physician if you experience urinary pain when taking supplements containing mega-doses of riboflavin, since this may indicate that your bladder lining is damaged -- a condition called interstitial cystitis.

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