CHARACTERISTICS OF THE WATER-SOLUBLE VITAMINS
B VITAMINS a group of water-soluble vitamins that serve as coenzymes in the conversion of carbohydrates, fat, and protein into energy
COENZYME a compound that binds to a protein (enzyme) and is required for its function or activity
ENERGY METABOLISM a series of reactions in the body that result in energy production
Water-soluble vitamins include eight B vitamins, vitamin C, and the vitamin-like nutrient, choline. The B vitamins function primarily as coenzymes, chemical compounds that bind enzymes and are required by the enzymes to carry out their function or activity. As coenzymes, they participate in energy metabolism, a series of reactions in the body that results in energy production, as well as myriad other types of reactions. In addition to functioning as a coenzyme in several types of reactions, vitamin C also serves as an antioxidant, protecting cells from free-radical damage. (INFOGRAPHIC 11.1)
INFOGRAPHIC 11.1 Properties of the Water-Soluble Vitamins
Unlike fat-soluble vitamins, which leave the small intestine in chylomicrons via the lymph and are stored in the body like fat, water-soluble vitamins immediately enter the blood following absorption, where most circulate freely. Because the water-soluble vitamins are not stored in large quantities, we must consume adequate amounts of them consistently. In addition, foods must be handled with care to preserve vitamin content; some vitamins (both fat- and water-soluble) are unstable and can be destroyed by ultraviolet light, as well as by cooking and storage methods. When you boil foods that contain water-soluble vitamins, for instance, a percentage of the vitamins typically leach out into the cooking water. However, steps can be taken to help preserve vitamins in foods. (INFOGRAPHIC 11.2)
INFOGRAPHIC 11.2 Preserving Vitamins in Foods
When we consume more of a water-soluble vitamin than we need, our body typically eliminates the excess through our urine. Individuals are much less likely to experience toxic adverse effects due to overconsumption of water-soluble vitamins than they are if they consume too many fat-soluble vitamins. In fact, toxicity or adverse effects from high intake of the B vitamins from food sources alone has almost never been observed. However, the use of dietary supplements can push intake well above recommended intake levels. (Chapter 12 will further explore the potential benefits and risks of dietary supplements.) Tolerable Upper Intake Levels (ULs) have not been established for all of the water-soluble vitamins, but ULs exist for niacin, vitamin B6, folate, vitamin C, and choline.
In the United States and countries with an adequate food supply, deficiencies of water-soluble vitamins are rare. However, there are circumstances when the risk of deficiency is higher; when calories are restricted, for example, or under conditions that affect absorption, such as diarrhea; parasitic, bacterial, or viral gastrointestinal infections; and intestinal disorders. (INFOGRAPHIC 11.3) In addition, the body’s need for most water-soluble (and fat-soluble) vitamins is higher during certain life stages, such as in the elderly, and during pregnancy and lactation, increasing the risk of potential deficiency and the associated consequences. When we suffer from fevers or injuries, and when we recover from surgery, we also need higher-than-normal amounts of water-soluble vitamins.
INFOGRAPHIC 11.3 Possible Causes of Vitamin Deficiencies Although serious vitamin deficiencies are relatively uncommon in developed countries like the United States, various factors can conspire to cause obvious signs and symptoms of deficiency in some individuals. In contrast, it is likely that a significant number of individuals in the United States have chronically low intake of one or more vitamins resulting in subclinical deficiencies that cause no overt symptoms.
Question
11.1
What members of society do you think have the highest risk of vitamin deficiencies?
The members of society at highest risk of vitamin deficiencies include individuals who live in poverty, those who are chronically ill, and those who are addicted to drugs or alcohol.
In the early days of the twentieth century, it wasn’t easy to accept that a poor diet could cause pellagra’s varied signs and symptoms, such as skin lesions, confusion, and diarrhea. Some suspected moldy corn caused the illness, or disease-carrying mosquitos. Even when individuals regained their health when fed a varied and wholesome diet, many doctors thought Goldberger’s ideas about pellagra were ridiculous. To prove them wrong, in a final jaw-dropping experiment conducted on April 26, 1916, Goldberger injected five cubic centimeters of blood from someone suffering from pellagra into his assistant, Dr. George Wheeler. Wheeler did the same to Goldberger. They swabbed secretions from the noses and throats of pellagra sufferers and rubbed them onto their own noses and throats. They even swallowed pills containing scabs of pellagra rashes. If pellagra were caused by a germ, they reasoned, they would undoubtedly fall ill. They did not.
Goldberger’s uncouth experiments eventually convinced many doctors that pellagra was not an infectious disease, but Goldberger didn’t live to figure out exactly what kind of nutritional deficiency caused pellagra. He died of cancer in 1929, leaving it up to someone else to track down the exact culprit.