After taking a vitamin supplement , most people notice that their urine turns a bright, almost fluorescent yellow. This characteristic, completely harmless, is mainly linked to the presence of a water-soluble vitamin, called riboflavin or vitamin B2 .
When we take a riboflavin-rich multivitamin supplement, not all of the ingested portion is actually absorbed. The surplus, thanks to the water solubility of the substance, is eliminated in the urine, which acquires the classic fluorescent shades. Like all water-soluble vitamins, the body is able to eliminate the excesses of riboflavin without showing particular signs of toxicity, however possible when the doses are clearly high. With a daily requirement of about 1.3 mg, intestinal absorption, which takes place in the small intestine , is saturable, so doses far higher than the RDA are only useful for producing particularly expensive urine (the maximum absorption capacity is around 25 mg).
To reduce the phenomenon of intense yellow coloration of the urine, it is possible to divide the tablet into two parts to be taken at different times of the day, preferably in conjunction with main meals.
