Gabe's elderly neighbor told him that when he was growing up, the milkman would deliver glass bottles of milk to his family’s doorstep. He wonders why milk is not available in glass bottles anymore. Gabe explains to him that light destroys certain water-soluble vitamins in milk and milk is now stored in opaque containers to protect _______ from destruction.

Riboflavin, also known as vitamin B2, is one of the eight B vitamins that are essential for human health, which are all water soluble. It is a vitamin found in food and used as a dietary supplement. It is involved in many processes in the body and is necessary for normal cell growth and function. It can be found in certain foods such as milk and other dairy products, meat, eggs, mushrooms, nuts, almonds, enriched flour, and green vegetables. Riboflavin is frequently used in combination with other B vitamins in vitamin B complex products. Some people take riboflavin by mouth to prevent low levels of riboflavin (riboflavin deficiency) in the body, for various types of cancer, and for migraine headaches. It is also taken by mouth for acne, muscle cramps, burning feet syndrome, carpal tunnel syndrome, and blood disorders such as congenital methemoglobinemia and red blood cell aplasia. Some people use riboflavin for eye conditions including eye fatigue, cataracts, and glaucoma.

Riboflavin was discovered in 1920, isolated in 1933, and first made in 1935. It is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. Riboflavin is available as a generic medication and over the counter.