Fundamentals of Human Nutrition/Riboflavin
Riboflavin can be found in a large variety of different foods. Legumes, vegetables, and seafood all contain significant amounts of riboflavin. While these products do contain substantial quantities of riboflavin, they are typically not the most riboflavin dense foods. One of the richest sources of riboflavin are milk products. One cup of 2% fat milk satisfies 29% of one’s daily value recommended intake of riboflavin. One cup of plain yogurt fulfils 35% of one’s daily value recommended intake of riboflavin. To compare, one cup of kidney beans meets only 6% of the daily value and three ounces of salmon satisfy merely 12% of one’s daily value recommended intake (USDA, 2014).
Aside from milk products, there are many other rich sources of riboflavin. The milling process of refined grains result in a significant loss of riboflavin. However, the enrichment process of fortified grains make products like breakfast cereal and bagels some of the best sources of riboflavin. One serving of some fortified breakfast cereal can satisfy 100% of one’s daily value recommended intake of riboflavin. To a lesser extent, whole grain/wheat products are also a great sources of riboflavin. The riboflavin density of whole grain/wheat foods is typically less extreme than fortified foods because nutrient compositions aren’t artificially modified. Nonetheless, their contribution to one’s daily value of riboflavin can still be quite significant with a single slice of whole wheat bread containing 6% of one’s daily value of riboflavin (USDA, 2014). Another excellent source of riboflavin is red meats. A three ounce piece of grilled beef satisfies roughly 24% of riboflavin daily value and a three ounce cut of lamb fulfils 105% of daily riboflavin intake. One of the largest known sources of riboflavin is beef liver. Cattle liver is one of the most nutrient dense foods in general, and riboflavin is no exception. A three ounce piece of cattle liver contains nearly 170% of one’s daily value of riboflavin (USDA, 2014).
Riboflavin is a water soluble vitamin and vulnerable to inactivation when exposed to ultraviolet light (Kumar, 2004). For this reason, sources of riboflavin must be stored in opaque containers and away from the sun in order to prevent riboflavin loss. Riboflavin isn’t completely fragile, its stability as a vitamin is actually quite strong. It can endure exposure to relatively extreme heating conditions and normal cooking processes (Choe, 2005). For these reasons, it is only important to be concerned over the storage of a riboflavin source as it relates to ultraviolet light.
1. Choe, E., Huang, R. and Min, D. B. (2005), Chemical Reactions and Stability of Riboflavin in Foods. Journal of Food Science, 70: R28–R36.
2. Kumar V, Lockerbie O, Keil SD, Ruane PH, Platz MS, Martin CB, Ravanat JL, Cadet J, Goodrich RP (2004). "Riboflavin and UV-light based pathogen reduction: extent and consequence of DNA damage at the molecular level". Photochemistry and Photobiology 80: 15–21.
3. U.S. Department of Agriculture, Agricultural Research Service (2014). USDA National Nutrient Database for Standard Reference, Release 28.
The water-soluble vitamin Riboflavin, also known as B2, functions in energy metabolism, as an antioxidant, as a coenzyme in many areas, and in redox reactions. Like other B vitamins, riboflavin helps the body convert carbohydrates, fats and proteins into glucose for fuel for the body. In energy metabolism riboflavin is in its coenzyme forms of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) and functions as a hydrogen/electron carrier. Riboflavin also works in combination with some other B vitamins, B6 and folate, in a process in the body that changes these into useable forms. Riboflavin is essential in growth processes and red blood cell production as well.
The electron transport chain is explained in a series of five complexes, of those complexes FMN functions in complex I and FAD in complex II. In the electron transport chain, FAD serves as an electron carrier and accepts electrons to become FADH2. FADH2 then gives its electrons to complex II of the chain that forms ATP molecules that act as energy.
Riboflavin also serves as an antioxidant that is used as a defense by the body to neutralize free radicals and prevent them from multiplying and causing cell and DNA damage. Antioxidants donate electrons to the unstable free radicals making them neutral and therefore unable to harm the body.
Because of its vital functions, riboflavin has medical implications and is used in an attempt to treat some ailments. Riboflavin supplementation may be beneficial in the treatment of migraine headaches, riboflavin deficiency, high homocysteine levels, and cataracts.
• Migraines: Riboflavin cannot reduce the pain or duration of the migraine but may be effective if taken at 400 mg/day in reducing the number of migraine headaches. • High homocysteine: People who suffer from hyperhomocysteinemia, or high amount of homocysteine in the blood, may find taking supplemental riboflavin to be beneficial in lowering the levels. Some people are unable to convert homocysteine into the functioning amino acid form methionine used by the body and therefore suffer from high levels of homocysteine in the blood. Taking riboflavin has shown in studies to help lower homocysteine blood levels in people with this condition. • Cataracts: Because of riboflavin’s function as a coenzyme in bodily processes it has been seen as an effective supplement in the reduction of cataracts. Riboflavin, in combination with the other B vitamins, helps to promote healthy vision and without all the B vitamin components, vision processes will be impaired. Because the combination of B vitamins is needed for normal vision, riboflavin supplementation will be most useful in combination with a niacin supplement in reducing a person’s chance of developing cataracts.
As stated earlier riboflavin, or vitamin B2, is fundamental in the process of metabolism in all of the macro-nutrients. More specifically it plays an important role during the step of energy release from carbohydrates, proteins, and fats. This same energy is what is used to contract muscles, power cells, generate new cells, and fight off bacteria. Based on this knowledge, it is clear to see that a deficiency in riboflavin would be completely detrimental for overall health. Some of the symptoms that would mark a riboflavin deficiency include:
-Sensitivity to light
-Itching and burning of the eyes
-Inflammation in the mouth
Organ failure will begin with the adrenal glands, which secrete and metabolize hormones with enzymes. These hormones spur on many major bodily functions.  Without the energy to drive or make more enzymes, the adrenal gland fails to dispense out hormones in the bloodstream. Vitamin B2 deficiency is commonly linked to alcoholism, dietary inadequacy, and people with blood disorders.
The most common of the causes is dietary inadequacy. Kwashiokor and Marasmus disease, in which there is insufficient protein and energy intake, the individual may lack in essential B vitamins. This includes riboflavin as described by Dr. Von Castel-Roberts. Vitamin B2 is common in plants and animals for necessary basic biological function. When we consume them, we absorb all of their vitamin B levels as well. This is due to that the entire food chain begins with plants which is consumed by animals and eventually consumed by humans. Humans can either take in the B2 through consumption of the animal or the plant.  Regardless, riboflavin is not a scarce vitamin in everyday life.
There are groups of individuals identified to have insufficient levels of riboflavin. Watch out for elderly folks whose primary source of caloric intake is tea and toast.  People with infections, liver disease, or are severe alcoholics are also prone to deficiency.
Vitamin B2 supplements should be taken in quick response to low levels to keep important bodily functions going.  The daily recommended dietary allowance is 1.3 mg for adult men, 1 mg for adult women, 1.1 mg for pregnant women, and 1.6 mg for breastfeeding women. For adults with low levels of riboflavin, treatment dosage should be at least 5 mg daily and no more than 30 mg daily, all in divided doses. Simply eating at least the recommended amount of riboflavin, which can be reached by following the examples in “MyFoodPlate”, attains many benefits. Cataracts in the eyes can be prevented. Reduction of homocysteine levels in the blood can also occur by converting it into methionine.  And for serious migraine issues, taking high doses of riboflavin (about 400 mg) reduces the number of attacks.
 Riboflavin Deficiency. (n.d.). Retrieved November 28, 2015, from http://emedicine.medscape.com/article/125193-overview
 Riboflavin vitamin B2 deficiency. (n.d.). Retrieved November 28, 2015, from http://www.vitamins-supplements.org/riboflavin-deficiency.php
 Riordan HD, Mikirova N, Taylor PR, Feldkamp CA, Casciari JJ. (2012). The Effects of a Primary Nutritional Deficiency (Vitamin B Study). Food and Nutrition Sciences, Vol. 3 No. 9
 Vitamin B Complex , Robinson, Frank Alfred, 1874-1951.
 Von Castel-Roberts, Kristina. (2015) Water-soluble Vitamins. University of Florida. McCarty Hall C Auditorium, Gainesville, Fl. Lecture.
Riboflavin is known more for its deficiencies, not for essentially being non-toxic. For instance, riboflavin wasn’t given an Upper Intake level (IU) in 1998 when the Recommended Dietary Allowance was updated. There are no known adverse or toxic effects of excess riboflavin, but there is the potential that it could increase the risk of breaking DNA strands, but only in the presence of a carcinogen called chromium (VI). In high-dose riboflavin therapy, there are cases of a harmless reaction where urine turns bright yellow or orange; this is called flavinuria.  With this B2 vitamin, even extremely high dosages have very rare side effects. While excluding flavinuria, some of these side effects can include itching, numbing sensations, and induced eye damage from the sun. This is reported by taking more than 10 mg of riboflavin per day. It should be noted that supplements usually contain 20-25 mg of B2 and 400 mg when taken at therapeutic dosages. 
Typically it’s easy for us to reach very high levels of riboflavin because supplements contain levels of B2 that are beyond the daily requirements with 10 to 100s of mgs. There can be risks associated with these high levels of riboflavin in combination with other factors. B2 and the combination of light can lead to adverse reactions as well. Riboflavin in our eyes and skin contributes to the negative effects due to UV light exposure, such as connective tissue damage, induction of DNA lesions, and mitochondria impairment. In animals, research found that high doses caused cellular damage to the retina of the eye. When there is that excess riboflavin in the body, blood, tissues, and urine levels greatly increase their levels of free riboflavin. Free riboflavin is dietary riboflavin not being used in the B2 dependent enzymes. 
As for drug interactions with riboflavin, women who regularly take high dose oral contraceptives were indicated diminished riboflavin status in early reports. However, the investigators who did controls on B2 intake found no differences between the female contraceptive users and non-users. Chronic consumption of alcohol has also shown to be associated with riboflavin deficiency, which was demonstrated in studies where rats were fed alcohol which led to impairment of intestinal absorption and renal uptake. 
In conclusion - most reports about riboflavin stand by their argument that it is harmless in large doses and non-toxic. However, one should be aware of the contradicting reports that exist but be conscious of the interactions riboflavin has with drugs and the high levels that exist with supplementation.
 Excess Vitamin B2 - Riboflavin Can Be Toxic! (n.d.). Retrieved December 1, 2015, from http://www.smart-publications.com/articles/excess-vitamin-B2-riboflavin-can-be-toxic#fn-117-1
 Higdon, J. (2000). Riboflavin. Retrieved November 30, 2015, from http://lpi.oregonstate.edu/mic/vitamins/riboflavin#drug-interactions
 Terry, S. (2015, September 3). Vitamin B2 Toxicity. Retrieved December 1, 2015, from http://www.livestrong.com/article/274360-vitamin-b2-toxicity/
"Riboflavin." Riboflavin. Web. 22 Aug. 2015.
Riboflavin (vitamin B2) deficiency. (n.d.). Retrieved October 23, 2015.
Riordan HD, Mikirova N, Taylor PR, Feldkamp CA, Casciari JJ. (2012). The Effects of a Primary Nutritional Deficiency (Vitamin B Study). Food and Nutrition Sciences, Vol. 3 No. 9
Vitamin B Complex , Robinson, Frank Alfred, 1874-1951.
"Vitamin B2 (Riboflavin)." University of Maryland Medical Center. Web. 22 Aug. 2015.
Von Castel-Roberts, Kristina. (2015) Water-soluble Vitamins. University of Florida. McCarty Hall C Auditorium, Gainesville, Fl. Lecture.
Whitney, E., & Rolfes, S. (2002). Understanding nutrition (9th ed.). Belmont, CA:Wadsworth.