On to vitamin B2, also known as riboflavin. Riboflavin, like thiamin, does a lot of things. It helps absorb and use iron. It supports eye heath. It prevents oxidative stress (which I think of as “rusting” in the body—basically, wear and tear on the tissues). It also supports methylation (which I think of as the oil in your body’s engine—it helps make sure cells are running smoothly). It can support energy during exercise, can be used (in high doses) to treat migraines, and can also help with healthy blood pressure. As with all the B vitamins, it plays a critical role in energy metabolism – breaking down carbohydrates, proteins, and fats. More than any other vitamin, though, riboflavin is critical for burning fat. Yet despite its importance, riboflavin deficiency is common. According to one study, nearly 40% of healthy adults are deficient in riboflavin.

What increases your body’s need for riboflavin? Burning fat—either through diet or through exercise. This is because riboflavin is a precursor two key molecules in fat metabolism: flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Without riboflavin, you can’t make these two molecules, and fat metabolism (specifically, beta-oxidation of fatty acids) gets backed up.

What happens if you don’t have enough riboflavin? All the things it helps with mentioned above won’t work as well. Additionally, there are a few specific symptoms that we typically think about with riboflavin deficiency (also known as ariboflavinosis). These include cracking and sores at the corners of your mouth (angular cheilitis), swelling and redness of the tongue (glossitis), greasy and scaly skin rashes (often affecting areas by the nose and ears), sensitivity of the hands and feet, and anemia. Irritated skin areas may also end up being infected with candida. Additionally, because riboflavin can affect energy production and fat metabolism, deficiency can lead to a buildup of fat metabolism products (fatty acids), which can contribute to things like fatty liver disease.

How much riboflavin do you need? The recommended daily allowance (RDA) for riboflavin for adults is 1.3 mg/day for men and 1.1 mg/day for women. This recommendation is based on the average requirements from population reference data. However, many people may need more than this. For example, people engaged in regular aerobic activity need more; people who are losing weight need more; people who have high fat diets need more. Sunlight exposure increases needs as well—when riboflavin is exposed to light, it breaks down—so people who spend a lot of time in the sun may need extra (though exactly how much extra will vary from person to person). People with MTHFR variants may also need more riboflavin. Riboflavin is a key cofactor supporting this enzyme function and specifically, people with C677T variants need twice as much riboflavin as those with a standard variant. Without changing anything else, supplementing with even small amounts of riboflavin can reduce homocysteine levels (a marker for methylation efficiency) by 22% in individuals with two copies of C677T. Anyone with gut issues (low stomach acid, low digestive enzymes, intestinal inflammation, etc) may be less able to absorb riboflavin from the diet, and people with chronic health conditions may lose riboflavin more quickly. For these reasons, it may be reasonable to adjust the target higher for many people—perhaps somewhere between 2 and 5 mg. That being said, the best way to know your riboflavin status is to check it. Riboflavin can be checked with advanced micronutrient testing, like a Nutreval panel, or from whole blood riboflavin (from a commercial lab).

How do you boost your riboflavin? The best way is usually through food. Foods high in riboflavin include nuts and seeds, lean meats and fish, eggs, green vegetables, dairy products, and organs meats (like liver, kidney and heart—which, admittedly, are not commonly part of modern diets, but have very high levels of riboflavin). Many foods (cereals and breads) are fortified nowadays, so can also be a source of riboflavin. Riboflavin can also be taken as a supplement. It’s in most multivitamins and tends to come in two forms: free riboflavin and riboflavin-5-phosphate (sometimes also called flavin mononucleotide, or FMN). FMN is sometimes called “activated” riboflavin—it is the form that is directly used by the body. However, FMN is converted into free riboflavin in the gut prior to absorption, so it is unlikely that FMN is a better supplement than plain old riboflavin (though it is more expensive). Most supplements have doses that are substantially higher than the RDA, ranging from 100-400 mg. You’ll notice that this number significantly exceeds the RDA, but high doses have no known toxicity, since riboflavin is a water-soluble vitamin (and any you don’t need gets eliminated), and high doses (400 mg) are sometimes used for treatment or prevention of migraines.

It's worth noting that if you take supplemental riboflavin, your urine will turn bright yellow. This is normal. It doesn’t mean the supplement isn’t working, and it also doesn’t mean that you aren’t absorbing it—sometimes higher concentrations may actually be needed to support absorption (if you have a chronic disease such as diabetes, or if your gut isn’t working well).

In summary, riboflavin—vitamin B2—is a critical vitamin for overall health, supporting metabolism (especially fat metabolism), iron metabolism, eye health, and methylation while preventing oxidative stress. It’s present in a varied diet, with good sources including greens, seeds and nuts, eggs, and lean meats and fish. It can be taken supplementally and is usually part of a multivitamin. There’s no known toxicity of high doses, though most supplements have way more than the RDA (sometimes more than 100 times). The RDA is 1.1 to 1.3 mg; many people may need more than that by 2x or 5x (though probably not 100x!). The best way to know if you need riboflavin is to test for it!

What’s your riboflavin status?

References

1.         McNulty H, Dowey LRC, Strain JJ, et al. Riboflavin Lowers Homocysteine in Individuals Homozygous for the MTHFR 677C→T Polymorphism. Circulation. 2006;113(1):74-80. doi:10.1161/CIRCULATIONAHA.105.580332

2.         PhD CM. Vitamin B2: Riboflavin. Harnessing the Power of Nutrients. Published June 27, 2022. https://chrismasterjohnphd.substack.com/p/vitamin-b2-riboflavin

3.         Emerging roles for riboflavin in functional rescue of mitochondrial β-oxidation flavoenzymes - PubMed. https://pubmed.ncbi.nlm.nih.gov/20858216/

4.         McNulty H, Pentieva K, Ward M. Causes and Clinical Sequelae of Riboflavin Deficiency. Annu Rev Nutr. 2023;43:101-122. doi:10.1146/annurev-nutr-061121-084407

5.         Riboflavin as a photosensitizer. Effects on human health and food quality - Food & Function (RSC Publishing). https://pubs.rsc.org/en/content/articlelanding/2012/fo/c2fo10246c

6.         McNulty H, McKinley MC, Wilson B, et al. Impaired functioning of thermolabile methylenetetrahydrofolate reductase is dependent on riboflavin status: implications for riboflavin requirements. Am J Clin Nutr. 2002;76(2):436-441. doi:10.1093/ajcn/76.2.436

7.         Powers HJ. Riboflavin (vitamin B-2) and health. Am J Clin Nutr. 2003;77(6):1352-1360. doi:10.1093/ajcn/77.6.1352

8. Jungert A, McNulty H, Hoey L, et al. Riboflavin Is an Important Determinant of Vitamin B-6 Status in Healthy Adults. J Nutr. 2020;150(10):2699-2706. doi:10.1093/jn/nxaa225