A Background on Vitamin A: Have you got what it takes?

Abstract

A B ackground on V itamin A: B S J H ave you got what it takes ? Sushrita Neogi Vitamins. We have all heard of them. Men’s, women’s, 50+, once daily. Vitamins are ubiquitous in clinical nutrition literature, in grocery stores, and on the news, but what exactly are they? Originally called vital- amines, vitamins are compounds (as opposed to trace elements) found in food that the body requires in small quantities to function properly. Vitamin deficiencies can cause a wide range of maladies that can be cured simply by replenishing the body with the lacking vitamin. The discovery that small amounts of vitamins can be used to cure certain diseases led to the Casimir Funk’s proposal of the Vital-amine Theory of Disease. However, even though many diseases are caused by a vitamin deficiency, the opposite can also be true, in which case an overdose of a vitamin can cause disease and deformities. Vitamins are either fat-soluble or water-soluble, which determines how they are transported through the body. Over-consumption is only a problem concerning fat-soluble vitamins, the category to which Vitamin A belongs. For the vitamin to be properly absorbed into the body from food, it must be absorbed alongside fat. Fat is absorbed through various organs: a properly functioning liver/gallbladder secretes bile acids to emulsify fat globules, the pancreas secretes lipase (a fat digesting enzyme), and the small intestine absorbs the nutrients. The process is complex and has high energy consumption, but is essential. Fat-soluble vitamins can be stored in the body’s adipose tissue and liver for time periods up to months or years. Water-soluble vitamins such as vitamins B or C, on the other hand, are easier to absorb, but are “Vitamins are ubiquitous in clinical nutrition literature, in grocery stores, and on the news, but what exactly are they?” easily excreted in urine. Thus, water-soluble vitamins are not stored in the body for any significant amount of time. The potential for long-term storage of fat-soluble vitamins can be useful, but also increases the risk of overdosing. We have traced the entry of vitamin A into the body, but where does it come from in the first place? As a fully formed vitamin, it is only found in foods of animal origin, especially liver, milk, and eggs. However, vegetables such as carrots and leafy greens, such as spinach, kale, and collard greens, have compounds called carotenoids, Figure 2. Disproportionate limb regeneration in newts with increasing doses of retinoic acid. also referred to as pro-vitamin A because they can be converted to vitamin A in the body after ingestion. Once inside the body, vitamin A, also called retinol, has many functions. First it is converted into one of two products: either retinal or retinoic acid. Retinal is produced in large quantities and is used by the body for vision-related purposes. Retinoic acid has a wider array of functions. It plays an integral part in maintaining growth and development, reproduction, the epithelial system, the immune system, and the nervous system. Vitamin A deficiencies and overdoses both wreak havoc on these essential body functions. One of the reasons why vitamin A overdose can cause issues is because it is a teratogen, a compound that, when consumed in excess, can cause developmental disorders. A striking example of the teratogenic capabilities of vitamin A is shown in an experiment that examined newt limb regeneration (Dmetrichuk, Spencer, & Carlone, 2005). When a newt with an amputated limb is given one dose of vitamin A, it is able to properly regenerate the 1 • B erkeley S cientific J ournal • S cience of F ood • V olume 16 • I ssue 1