Vitamins of the B Complex

GRACE A. GOLDSMITH.

AN investigation of beriberi in the late 19th century started the chain of events that led to the discovery of vitamins. Beriberi had long been a common and a serious disease in parts of the world where polished rice was the staple food.

Christiaan Eijkman, a Dutch surgeon, was carrying out studies on fowls in a military hospital in Java in the 1890's. To save money, he fed them scraps mostly polished rice--from the patients' meals. The fowls unexpectedly developed a bad nerve ailment, which resulted in paralysis.

Somewhat later the director of the hospital withheld permission to use the scraps, and Dr. Eijkman had to buy natural or undermilled rice for the chickens he used in his experiments. The ailing birds improved after they began eating the natural rice.

Dr. Eijkman then began a series of experiments that led to the first clear concept of disease due to nutritional deficiency. He fed polished white rice to pigeons, chickens, and ducks. They developed the paralysis he had observed previously, and they recovered when he fed them natural rice. Birds fed whole rice remained well.

He noted that the disease that resulted from a polished rice diet in birds resembled beriberi in man.

He believed that rice contained too much starch, which poisoned nerve cells, and that the outer layers, removed from the grain in milling, were an antidote. His report was published in Dutch, and some time elapsed before it was known generally.

G. Grijns, another Dutch physician, interpreted Dr. Eijkman's findings in a different way. He concluded in 1901 that beriberi in birds or man was due to a deficiency or absence of an essential nutrient from the diet.

From then on, chemists in many countries tried to concentrate the substance in rice that prevented beriberi in order to obtain it in pure form. Among them was Casimir Funk, of the Lister Institute, London, who coined the term "vitamin" and applied it to the antiberiberi substance.

B. C. P. Jansen and W. P. Donath in Holland in 1926 isolated the anti-beriberi vitamin, and in the 1930's Robert R. Williams and his associates determined its structure and synthesized it.

Thus men discovered the cause and cure of beriberi, which nevertheless remains a serious disease today in countries in which overpolished and overmilled rice is a staple in the diet.

During the first stages of separating and identifying vitamins, the designation "water-soluble B" was given by Dr. Elmer V. McCollum and Marguerite Davis to the concentrates that cured beriberi. Vitamin B at that time was thought to be a single substance. Later research showed that it consists of a number of substances that differ widely in chemical structure but have much the same natural distribution in foods.

Of the 11 substances in the vitamin B complex that now are available in pure form, five are components of one or more coenzymes thiamine, riboflavin, niacin, pyridoxine, and pantothenic acid. Coenzymes are catalysts that have important and often related functions in the biochemical processes by means of which nutrients are used for energy and for building up or maintaining the cells and tissues of the body.

Two of the B vitamins, folic acid and vitamin B₁₂, have antianemic properties and presumably exert their function in a similar way that is, as coenzymes.

These seven vitamins are essential in human nutrition and must be included in the daily diet.

Of the other four members of the B complex, choline is important in human nutrition but is probably not an essential dietary constituent because the body can form it from other compounds.

Very likely biotin is required by man, but it is furnished by bacterial synthesis in the intestinal tract as well as by food.

Inositol and p-aminobenzoic acid, other members of the B complex, have not been shown to be essential in human nutrition.

A LACK OF VITAMINS of the B complex is one of the forms of malnutrition that often occur throughout the world. Because of the similar distribution of the B vitamins in foods, a deficiency of several factors is observed oftener than a deficiency of a single substance. The interrelationship of many of these vitamins in life processes means that signs of deficiency often are similar when the diet lacks any one of several factors. Many physiologic and pathologic stresses influence the need for the B vitamins. Larger amounts are needed during growth and in pregnancy and lactation than in maintenance of health in adult life. The requirement may be increased by diseases that elevate metabolism and by conditions associated with poor absorption, improper utilization, or increased excretion. Administration of antibiotics may lead to vitamin deficiency in some circumstances; in others, antibiotics spare vitamin requirements.

THIAMINE, or vitamin B₁, also known as the antineuritic or antiberiberi vitamin, is a water-soluble compound. It is readily broken down by heat in neutral or alkaline solutions. Its solubility and the ease with which it is destroyed are important, because overcooking food and discarding the water in which the food is cooked may cause large amounts of the vitamin to be lost.

Thiamine is present in many natural foods but is abundant in few. Lean pork is one of the best sources. Dry beans and peas, certain of the organ meats, and some nuts furnish sizable amounts. Whole wheat and enriched cereals and bread are dependable sources. They can contribute valuable amounts to the diet. The small amounts provided by other foods, such as milk, eggs, other meat, fruit, and vegetables, add up and represent a worthwhile contribution to the diet.

The thiamine requirement is related to caloric intake. The minimum need is approximately 0.20 to 0.23 milligram per 1,000 Calories. This requirement is based on experiments in which thiamine in the diet is restricted, on studies of diets of population groups, and on estimates of the amounts excreted in the urine of people having known intakes of thiamine.

The requirement of infants in relation to Calories appears to be comparable to that of the adult. Human milk supplies an average of 0.21 milligram per 1,000 Calories. We have evidence that the ratio of carbohydrate to fat in the diet influences the requirement.

The recommended dietary allowance for thiamine is 0.5 milligram per 1,000 Calories. When an adult's diet furnishes fewer than 2,000 Calories a day, the thiamine allowance should not be less than 1 milligram daily. This allowance provides a large factor of safety above the minimum need and seems desirable because requirements vary among individuals and because stores of thiamine in the body are not large and may be exhausted readily in diseases associated with an increase in metabolism.

Bacteria in the intestines may synthesize some thiamine, but the amount available to the human body to supplement the dietary supply seems to be small.

Thiamine is absorbed readily from the intestinal tract. It is excreted in the urine in amounts that reflect the amount taken in and the amounts stored in tissues. Measurement of the urinary excretion of thiamine after giving a small dose of thiamine is useful in determining whether body stores are adequate or deficient.

Thiamine functions in the body as a coenzyme, which is called cocarboxylase. It acts as a catalyst in one of the chemical reactions by which glucose (sugar) is broken down in the tissues to supply energy. These reactions proceed stepwise, and cocarboxylase acts at an intermediate stage when a substance known as pyruvic acid has been formed.

In thiamine deficiency, pyruvic acid accumulates in the blood and tissues and there is a change in the ratio of this acid to lactic acid. These metabolic changes are magnified by administration of glucose and by exercise and form the basis of a diagnostic test for thiamine deficiency. The concentration of glucose, lactic acid, and pyruvic acid in blood is determined after the administration of glucose and a standard amount of exercise. Results are expressed as a "carbohydrate index," which increases in thiamine deficiency.

Thiamine deficiency has been produced experimentally in people. Effects of a moderate shortage of thiamine include fatigability; apathy; loss of appetite; nausea; such psychic and personality disturbances as moodiness, irritability, and depression; a sensation of numbness in the legs; and abnormalities of the electrocardiogram.

Advanced deficiency of thiamine, or beriberi, is characterized by peripheral neuritis, heart disease, and edema. Peripheral neuritis is a disease of the nerves of the extremities, usually both legs are affected and sometimes the arms as well. The symptoms include loss of sensation, muscle weakness, and paralysis.

A deficiency of thiamine can also cause damage to the brain, which may be manifested by confusion, delirium, and paralysis of the muscles that move the eyeballs. This condition is called Wernicke's syndrome.

RIBOFLAVIN, formerly known as vitamin B₂ or G, is a water-soluble, yellow pigment. It is widely distributed in foods of plant and animal origin. It is stable to heat, especially in acid solutions, but it is destroyed on exposure to light.

Among the best sources of riboflavin are milk and variety meats, like liver, heart, and kidney. Other lean meat, cheese, eggs, and many of the leafy, green vegetables also furnish valuable amounts. Whole-grain and enriched cereals and bread, in the amounts in which they are eaten in this country, contribute important amounts of riboflavin to the diet.

Pasteurizing and drying milk do not lower its riboflavin content very much, but exposure to sunlight destroys large amounts of the vitamin.

The minimal daily requirement of riboflavin is about 0.6 to 0.7 milligram for adults and 0.4 to 0.5 milligram for infants. Considerable evidence indicates that an intake of 1.1 to 1.6 milligrams daily will provide adequate body stores.

The need for riboflavin does not seem to be related to caloric consumption but may be related to body weight. Both riboflavin and protein requirements are increased by similar conditions, such as growth, pregnancy, and lactation. Riboflavin allowances accordingly are computed from the protein allowances; a factor of 0.025 is used. Recommendations for men and women are 1.8 and 1.5 milligrams daily, respectively.