First among these we will consider the minerals found in foods. Those commonly named are calcium, phosphorus, iron, iodine, sodium, chlorine, copper, sulphur, potassium, magnesium, and manganese. Some others are present in traces. The amounts of each actually needed in the body vary considerably but they play an important part in the building and repairing of body tissue, and in the regulation of its processes.
Calcium. Calcium is one of the most important mineral elements. There is more calcium in the human body than any other element, and yet the average American diet is relatively more deficient in respect to this element than any other.
The chief function of calcium is the building of skeletal tissue, approximately 99 per cent being used for this purpose. The infant is born with a comparatively small amount of calcium and the need for it during infancy and adolescence for building strong bones and teeth is very great. If a sufficient supply is not included in the diet during pregnancy, calcium will be drawn from the bones and teeth of the mother. The need for this mineral during pregnancy is quite generally known, but the fact that the demand for it during the nursing period is even greater, has not been appreciated or emphasized.
Even though the supply of calcium and phosphorus in the bones and the teeth of the mother are drawn upon to supply these minerals to the infant, if the supply in the diet is inadequate rickets and poor tooth development will result. The gross symptoms of rickets arenarrow or deformed chest, contracted pelvis, knock-knees, and bow legs as well as malformed head and jaws, and teeth which are often irregular and subject to early decay.
While the building of bones and teeth is probably the most important function of calcium, and about 99 per cent is used for this purpose, the small amount used for other purposes is of extreme importance. It is necessary in the clotting or coagulation of blood. Heart muscle is made more sensitive by calcium salts circulating about it. Where there is a total lowering of the amount of this element in the blood, a peculiar type of muscle spasm, known as tetany, is seen.
Milk is without question the best source of calcium. Evidence at present seems to indicate that calcium is best absorbed in the form of di-calcium phosphate. In milk, an adequate amount of phosphorus in proportion to calcium is always available. Experiments have been con-ducted replacing milk with sufficient amounts of other foods to keep the calcium content of the diet constant, but the results have not been favorable. An interesting comparison of the calcium content of foods published in the Journal of the American Medical Association, showed the following:
1 quart milk 4 lb. cheese 50 apples (large) 32 lbs. string beans 9.4 lbs. beets 7 loaves white bread 5.5 loaves brown bread 11 lbs. butter 3.9 lbs. cabbage 3.7 lbs. carrots 1.5 lbs. couliflower 2.7 lbs. celery 27.5 lbs. green corn 20 eggs 7.3 lbs. grapefruit 12 lbs. grapes 1.8 lbs. lentils 2.3 lbs. oatmeal 4.9 lbs. oranges 12.9 lbs. pears 9.9 lbs. green peas 17 lbs. potatoes 17.6 lbs. rice 11 lbs. tomrtoes 26.4 lbs. watermelon 26.4 lbs. lean beef 14.7 lbs. fish 100 qts. water (Catskill and Croton)
Experiments conducted on healthy children indicate that a growing child needs a gram of calcium per day and that the best way to provide it is to include three cups of milk in the daily diet. Calcium balance experiments on adults reveal that as a minimum an average adult weighing 154 pounds requires 0.45 grams of calcium. It is estimated that pregnant mothers require 1.6 grams of calcium and nursing mothers still more. Sherman concludes from studies of American dietaries that optimum calcium for adults except pregnant and nursing women is 0.68 grams daily. One quart of milk contains 1.2 grams.
It is generally agreed that children should have a quart of milk daily. It is an excellent food in any period of life, and should not be restricted to infancy. Among primitive people or where milk is not available as a regular article of diet, strange customs in respect to special articles of food have been reported. Some eat fish bones and fish heads. Others eat green plants and shoots in season or may use the bones of birds or animals, some-times using them in the ash form or preparing them with vinegar to soften them. The use of primitive stone mills may have helped to supply minerals. The Chinese and others use the soy bean and its products which have a fairly good calcium content.
In our American dietaries the problem apparently would be solved if we could teach people to use more milk. Milk consumption has increased in recent years as its value has been pointed out, and yet even more should be used. Some interesting statistics show that the annual per capita consumption is as follows: U. S. 55 gallonsan increase from 43 gallons in 1920; Sweden, 70 gallons; Denmark, 68.5 gallons; Switzerland, 67 gallons; and Germany, 61 gallons.
Phosphorus. About 90 per cent of the phosphorus used in the human body is found in the bones and teeth. It also forms a part of every cell and is used in larger amounts than calcium in the soft tissues and fluids.
It has been shown that calcium and phosphorus must be used in correct proportions. Rickets can be developed on diets high in calcium and low in phosphorus or low in calcium and high in phosphorus. This does not happen when a liberal amount of both minerals is supplied and a surplus of about 50 per cent is advisable.
Milk is also an excellent source of phosphorus, a quart containing approximately 0.9 gram. Meat, fish, fowl, eggs, fruits, vegetables, and cereals are good sources. The average requirement for phosphorus is approximately twice that of calcium, standard figures giving 1.32 grams with 0.88 gram as a minimum. As with calcium, an extra amount is required during growth, pregnancy, and lactation. The American diet is apt to be low in phosphorus, but the deficiency is not nearly as great as that of calcium.
Iron. Although a very small amount of iron is needed it is one of the most important mineral elements and it would be impossible to sustain life without it. Iron enters into the structure of all cells and is the chief mineral constituent of hemoglobin, the compound that gives color to the red corpuscles in the blood and takes up oxygen which the blood carries to the cells.
These red cells are made in the marrow of the bone. Iron is used over and over again in the building of these cells, but there is a daily loss which must be replaced by food in the diet. Very little is stored in the adult although the infant is born with a reserve supply that lasts for several months.
A deficiency of iron in the blood is one of the chief findings in secondary anemia. This is due to the building of fewer red cells or a reduced hemoglobin content in those that are produced. An iron deficiency may be detected very quickly by clinical symptoms and laboratory tests. The number of red cells and the amount of hemoglobin in a cubic millimeter of blood has been determined and figures for healthy individuals show a hemoglobin of 85 to 95 per cent, and red cells from 4,500,000 to 5,000,-000.
Among foods, red meats (particularly liver, kidneys, and beef), egg yolk, whole wheat products, and green vegetables are the richest sources of iron. It is interesting to note that the amount of iron present in the yolk of an egg is proportional to the amount of greens eaten by the fowl. Potatoes, beans, peas, molasses, and strawberries are good sources; other vegetables and fruits contain some. The iron content of milk is very small but very effective, probably due to the form in which it exists, or because the calcium and vitamin content of the milk increases its utilization. The amount of iron in a food is not necessarily the measure of its value, as iron is difficult to absorb. The presence of copper and possibly certain vitamins may aid in the utilization of the iron.
The daily iron requirement is given as 0.015 gram, and because of the difficulty of absorption, a surplus should be supplied. Where a sufficient surplus cannot be provided in food the use of reduced iron, iron carbonate, or other salts of iron has proved of great benefit.
Iodine. Iodine, although required in but small amounts in the body, is nevertheless essential. It is used in the elaboration of the internal secretion of the thyroid gland. When a sufficient supply is not available an enlargement of the thyroid gland results. The enlarged neck so often seen in the adolescent period and during pregnancy, is usually due to an abnormal development of this gland, apparently in order that it may utilize to the utmost a too scanty supply of iodine.
Water has heretofore been recognized as the chief source of iodine to which may now be added the green vegetables, provided of course, the ground water where they are grown contains a sufficient amount of iodine. Other valuable sources are sea foods and sea salt.
There are certain districts in the world, notably Switzerland, the territory surrounding the Great Lakes, the Puget Sound region, and the Rocky Mountain district where the water is deficient in this mineral element. Some very careful and instructive work was originally done by Marine and Kimball on the children in the city schools of Akron, Ohio, where the effect of this iodine deficiency has been carefully estimated and successfully treated. The remedy is surprisingly simple. The prophylactic ad-ministration of 2 grams (30 grains) of sodium iodide twice yearly prevents the thyroid enlarging and causes a marked decrease in the size of those already enlarged. The use of iodized salt is becoming more and more general in districts where there is an iodine deficiency. In the state of Michigan where its sale is compulsory, it has been used universally for over ten years, and statistical studies show that the results have been good. It was feared for a while that the promiscuous use of iodized salt might be injurious to patients with toxic goiters. However, Plummer has shown that even when a patient has a toxic goiter the proper use of iodine not only decreases the toxicity of the goiter, but very materially decreases the operative risk when surgery must be undertaken. Iodine must, of course, be administered under the advice of a physician.
We have a peculiar situation in Southern California, which is well outside of the goiter districts, for the well waters contain from 6000 to 8000 parts of iodine per 100,-000,000,000 parts of water when 23 parts are sufficient to prevent the development of simple goiter. In a survey of the school children in Santa Barbara, Lamb found 11 per cent with definite evidences of goiter. This is due to the fact that with the increasing population, this city, as many others, is dependent for its water supply upon rain water impounded in large reservoirs. San Francisco se-cures its water supply from the snowfall on the Western slope of the Sierra Nevada mountains, and Los Angeles draws its water from the snows of the Eastern slope of the same range. In districts in those states where the water contains an insufficient supply of iodine, iodized salt or other iodine-containing foods or iodine-containing water should be used.
The other essential minerals in the list given above (sodium, chlorine, copper, sulphur, potassium, magnesium, and manganese) are probably supplied in the average diet without any special effort.
Sodium and Chlorine. These minerals are found in combination as sodium chloride or table salt. This sub-stance helps maintain the proper density of the body fluids and cells. In the wall of the stomach it is broken down chemically, contributing chlorine to the formation of hydrochloric acid, and sodium is released into the blood stream where it exists in several compounds. Of special importance are sodium carbonate (washing soda) and sodium bicarbonate (baking soda) which are intimately associated with the removal of carbon dioxide from the tissues to the lungs. There are other compounds of sodium in foods which contribute to the total needed by the body.
Most persons use more salt than is necessary, consuming about 15 to 16 grams where from 2 to 3 grams is all that is needed. Usually no attention is given to the use of an average amount, but when a test of the kidneys shows that their function has been seriously impaired in the presence of high blood pressure, the addition of salt to the diet should be forbidden. The daily excretion of salt which almost equals the intake is accomplished through the kidneys. When persons sweat profusely they lose large quantities of salt. One form of serious heat prostration at least partly due to a deficiency of sodium chloride will be discussed elsewhere. When the weather is such that people constantly sweat excessively, then added amounts of salt in the diet may be used to advantage.
Copper. Copper has been found to be necessary for the utilization of iron in the formation of hemoglobin, al-though it is not a constituent of hemoglobin. All the foods containing iron contain a small amount of copper and a diet supplying sufficient iron will not be deficient in copper.
Sulphur. Sulphur is taken into the body by reason of its being a constituent of proteins. It is found most freely in one of the proteins of milk (lactalbumin), egg yolk, vegetables of the cabbage family, and oatmeal. It is a constituent of most of the proteins of the body, and apparently is present in the greatest degree in the skin, hair, and nails. The daily need of the body is approximately 1.2 grams.
Potassium, Magnesium, and Manganese. These minerals are essential in small quantities for the normal functioning of the body, but since no deficiencies have been proved, it is necessary only to mention them in passing. Like many of the other minerals they are found in fruits and vegetables. Milk is a good source of magnesium.
The body obtains its water supply from the fluids taken in, from the food eaten, and from the end products of the process of oxidation within its tissues. A liberal quantity of water is available in milk, fruit juices, soups, tea, coffee, and other beverages. Fruits and vegetables contain a high percentage, but generally, we believe, some pure water should be taken as well. Other foods such as meat, bread, cereals, and dry crackers, all have some water in them.
Water is necessary as a dilutant in the preparation of many foods, or as a vehicle so that suitable cooking may be done as a step preparatory to digestion. In digestion itself often the chemical changes that take place are essentially produced by water uniting with food. When obtained from natural sources, many times important minerals are carried in solution, making it valuable in supplying other essential substances than fluid alone.
From experiments it has been reasoned that in quiet living about two quarts of water per day pass through the body, without figuring the amount that may result from the oxidation of food. Larger amounts of water than this probably are of no particular value.
A more detailed discussion of the uses of water will follow in a separate chapter.
Fiber, or cellulose, is the indigestible part of the fruits, vegetables, whole grain cereals, and breads. It stimulates peristaltic movement of the intestines, thus aiding the digestion and absorption of the other food elements. Further, it aids in the elimination of waste products. An excessive amount of fiber, however, may interfere with absorption and prove irritating to the mucous membrane of the intestines, bringing about an accumulation of gas or a too rapid emptying of the bowels. A liberal amount of fruits, leafy vegetables, whole grain cereals, and breads well distributed among the three meals will usually pro-vide the fiber normally needed.