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Riboflavin (B2) in dog and cat diets

A short guide to the role of Riboflavin (B2) in dog and cat nutrition.

Riboflavin is a water-soluble vitamin that acts as a catalyst in cellular respiration. It enables cells to obtain energy from nutrients and is crucial for healthy skin, fur and mucous membranes [1]. In the body, 90% is in active forms—flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD)—which contribute to macronutrient metabolism. The remaining 10% is in free form, as esters or as glycosides. Because it is water-soluble, vitamin B2 readily leaches into cooking water. It is temperature-resistant but extremely sensitive to sunlight (UV rays cause irreversible conversion), so supplements must be stored in opaque packaging. Drying in sunlight or cooking without a lid can also cause losses [2].

What it contains: Offal, egg yolks, brewer’s yeast and muscle meat [1].

Deficiency: Extremely rare (it occurs with starvation or intestinal disease). Signs include dry, flaky, reddened skin (around the eyes, muzzle and groin), dull fur, weight loss and cataracts or corneal opacity [3].

Excess: It is readily excreted; riboflavin toxicity has not been observed even at high doses [4]. A curious fact: excess riboflavin turns urine bright yellow, a “neon” colour that is completely safe and natural.

Sources

  1. National Research Council (2006). Nutrient Requirements of Dogs and Cats, ch. 6. National Academies Press. https://nap.nationalacademies.org/catalog/10668/nutrient-requirements-of-dogs-and-cats
  2. Beltramo, B., Urlings, M., Padilla-Díaz, C. M., Bast, A., Diliën, H., & De Boer, A. (2025). Bioavailability of vitamins C, B2 and B9 (Folate) in nutrition and health claims: A critical assessment. Food Production, Processing and Nutrition, 7(1), 55. https://doi.org/10.1186/s43014-025-00330-3
  3. Merck Veterinary Manual (2023). Nutritional Requirements of Small Animals. https://www.merckvetmanual.com/management-and-nutrition/nutrition-small-animals/nutritional-requirements-of-small-animals
  4. National Research Council (1987). Vitamin Tolerance of Animals. National Academies Press. https://www.nationalacademies.org/read/949/chapter/10