Vitamin B2 is of the vitamin B complex group. It is called riboflavin and is water soluble, so needs regular replenishing. It derives calories from carbohydrates, amino acids (proteins), and fatty acids. It helps to activate vitamin B6 (pyridoxidine), absorb iron and create vitamin B3 (niacin).
It helps with red blood cell production, antibody formation, cell respiration (use of oxygen), growth and assists the adrenal glands.
It eases watery eye fatigue, may help with prevention of cataracts. Keeps mucus membranes in the digestive tract healthy. It is needed for rapid growth periods (growth spurts) and during high protein diets. Good for healthy skin, eyes and nails.
Shortage is indicated by cracks and sores in the corners of the mouth, inflamed mouth and tongue, skin legions, eye disorders, dermatitis (skin problems), hair loss, dizziness, insomnia, light sensitivity, stunted growth, bad digestion, slow thinking and "burning" feet.
Having too much is harmless and will simply turn your urine yellow (bright yellow with vitamin pills!) as it passes through.
It might be a good idea to have more if you are using alcohol, hormone treatments, or antibiotics. Also if you are doing a lot of heavy exercise, are over-stressed, or on a low calorie diet.
Vitamin C and the rest of the vitamin B complex group are needed to get the best from your vitamin B2. Optimally vitamin B2 and vitamin B6 should be equal in quantity. Vitamin B2 is light sensitive (that is, destroyed by light).
It is found in offal (that is, organ meat, or sweetmeats), nuts, dairy products (milk, cheese, yogurt), eggs, meat, green leafy vegetables, fish, legumes and whole grains (most of which is shielded, note, from strong direct light). You can tell if something has B vitamins in it by a slightly bland taste in amongst it's palate.