Riboflavin or vitamin B2 is part of the group of vitamins referred to as vitamin B complex which makes it a water-soluble Vitamin*. As a drug, it is often prescribed in a combined formulation consisting of other B complex vitamins as a prophylactic supplement to prevent the development of deficiency.
Riboflavin deficiency is rare as it is ubiquitous in a variety of food choices. However, individuals following a diet scarce in milk and meat, which are one of the best sources of riboflavin, and also some specific groups of individuals as discussed below may be prone to its deficiency. 
Milk and dairy products have very high riboflavin content; its intake makes it the greatest contributor of the vitamin in Western diets, making riboflavin deficiency uncommon among water-soluble vitamins. However, in developed countries, there is increased intake of semi-skimmed milk, depleting milk of its riboflavin content. Although relatively stable, it is easily degraded by light. Milk kept in a glass bottle may be susceptible to degradation through this route.
Grain products possess low natural amounts, but fortification practices ensured that certain breads and cereals have become very good sources of riboflavin. Therefore, according to an article by Morgan KJ et al., high riboflavin levels were found in those having cereals for breakfast. Fatty fish are also excellent sources of riboflavin, and certain fruits and vegetables, especially dark green vegetables, contain reasonably high concentrations. Vegetarians with access to a variety of fruit and vegetables can avoid deficiency, although intake may be lower than omnivores, and elderly vegetarians are at a higher risk. 
Groups of Individuals at a Higher Risk for Low Riboflavin Intake
Pregnant/lactating women and infants
Pregnancy demands higher riboflavin intake as it crosses the placenta. If maternal status is poor during gestation, the infant is likely to be born riboflavin deficient. Breast milk riboflavin content may reflect maternal intake and can be moderately increased by riboflavin concentration of the mother when maternal intake is low.
Riboflavin deficiency among children is demonstrated in many regions of the world where they are deprived of adequate milk and meat in their diet. Riboflavin deficiency among children in the Western world seems to be largely confined to adolescents, especially girls, because of increased metabolic demand.
There is an increasing requirement of riboflavin with advancing age as a result of decreased efficiency of its absorption by the enterocytes.
Some studies report that vigorous exercise may deplete riboflavin due to its consumption in the metabolic pathways.
Young women practicing unorthodox eating habits accompanied by excessive exercise in order to lose weight have been shown to have low levels of riboflavin.
Prominent Features of Riboflavin Deficiency
Although clinical features of some vitamin deficiencies are similar and often coexist, the following are more common features of riboflavin deficiency are as follows:
Recommended Daily Allowance for Riboflavin
Apart from supplementation in deficiency, it is also prescribed in some clinical situations as follows:
Neonates undergoing phototherapy
Hyperbilirubinemia in the neonatal period is often managed with phototherapy. But it has been shown to degrade riboflavin and cause a deficiency in the newborns. A prophylactic daily oral dose of riboflavin prevents the development of the deficiency.
Antiretroviral induced lactic acidosis
This rare syndrome is caused by a group of antiretroviral drugs used to treat HIV infection called nonnucleoside reverse transcriptase inhibitors (NNRTI). Discontinuation of the drug along with treatment with riboflavin causes its reversal.
This is gradual corneal narrowing caused by an alteration in the collagen matrix in the stroma, resulting in protrusion of the cornea in an irregular pattern. Therapy was aimed at correcting the refractory error until 1990; however, now a radical approach targeting the pathophysiology of the disease by cross-linking the corneal fibers is undertaken where the superficial epithelium is removed, 0.1% riboflavin is applied for 30 minutes, and the cornea is treated with UVA for another 30 minutes. 
*Remember WBC = water-soluble vitamins B&C.
Riboflavin is involved in the metabolism of macronutrients as well as the production of some other B complex vitamins. It is known to participate in redox reactions in the metabolic pathways through cofactors flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), derived from riboflavin, by acting as electron carriers. Inadequate intake of riboflavin would be expected to lead to a disturbance in the intermediate steps of metabolism, with certain functional implications.
It is also known for its role as an antioxidant due to its involvement in the regeneration of glutathione, a free radical scavenger.
In addition, it is involved in growth and development, especially during fetal life, reproduction, and lactation.
A small amount of riboflavin is present in foods as free riboflavin, a majority as its derivative flavin adenine dinucleotide (FAD), and a smaller amount as flavin mononucleotide (FMN). A small amount, however, is also produced by the intestinal bacteria. 
For the absorption of dietary riboflavin, a prerequisite is the conversion of FAD and FMN to free riboflavin, catalyzed by enzymes called phosphatases in the enterocyte. Absorption of the vitamin takes place predominantly in the proximal small intestine through a saturable, active, carrier-mediated transport process.
Riboflavin is relatively safe to administer as excess is not absorbed by the enterocytes. Caution must be observed in the administration of large doses in pregnant women. It may cause urine discoloration (yellow-orange).
There are no absolute contraindications to riboflavin intake.
Blood levels and urinary excretion are not sensitive markers of riboflavin deficiency, and the preferred method for assessment of riboflavin status is stimulation of the FAD-dependent erythrocyte glutathione reductase. The results are expressed as an activation coefficient (erythrocyte glutathione reductase activation coefficient) such that the poorer the riboflavin status, the higher is the activation coefficient. 
Toxicity is infrequent when consumed orally from the diet; however, deleterious effects like hepatotoxicity, cytotoxicity, and damage to lenticular and retinal proteins, which are always exposed to light, can occur due to repeatedly taken pharmacologic doses. 
Riboflavin Deficiency Can Be Prevented by a Multidisciplinary Approach
Riboflavin is not stored in large amounts in the body; only small reserves exist in the liver, heart, and kidneys. Most people obtain riboflavin from their diet. There are many individuals on restricted diet plans and many who do not consume dairy; these individuals are prone to developing riboflavin deficiency. Other risk factors for riboflavin deficiency include pregnancy, poverty, old age, depression, breastfeeding, use of phototherapy, and poor cognition. Riboflavin deficiency can present with many clinical features and the quality of life can be poor. Hence, in view of these facts, an interprofessional team approach is required to prevent this nutritional deficiency. Pharmacists play a key role in the education of patients as they are the first-line professionals to see them. Nutritionists should emphasize the importance of adequate nutrition, exercise, and maintaining a healthy weight. The nurse also plays a critical role in educating pregnant mothers on the possibility of riboflavin deficiency when breastfeeding and the need to take supplements. Nurses who look after newborns who receive phototherapy for hyperbilirubinemia should be aware that this treatment can also cause riboflavin breakdown, and hence the need for supplements. For outpatients, a dietitian should be consulted to teach patients about foods that are rich in riboflavin. Most cases of riboflavin deficiency can be prevented by taking a proactive approach; this not only leads to a healthy population but also decreases healthcare costs.,,, (Level V)
When riboflavin deficiency is treated, the outcomes are good. The majority of symptoms improve within a few weeks or months. However, those who develop neurological abnormalities may have residual deficits that last a long time.  (Level V)