Vitamin A stimulates growth, but is necessary at all ages. Its deficiency results in loss of appetite, weakness, retarded growth, and' especially favors lowered resistance to infections or "colds" of the mucous membranes, such as in the eyes, ears, nose, sinuses, glands of the mouth and throat, the gastrointestinal tract, and sometimes the kidney (nephritis) and bladder (cystitis).
Its deficiency also causes gall-stones and gravel or sand in the kidney and bladder, secondary anemia, psoriasis, and favors dropsy from kidney trouble. Such cases, as well as cystitis and albuminuria in the urine without adequate cause in children, are successfully treated by its administration. Although the dissolving of kidney stones is a slow process, the administration of vitamin A promptly allays the irritation. Mottled, ruddy complexion, also "whiskey nose" dear up in a few days by the use of vitamin A.
Its use alone in an infectious attack is not sufficient to check it because vitamin B is also needed to promote toxic elimination, vitamin C to promote white-cell activity, and vitamin D to maintain the blood-calcium balance.
Spinach contains all the vitamins save F. The other salad greens are rich in A, B and C. Vitamin A helps constipation by its stimulating action on the liver. It is the distributor of potassium to the nervous tissues. Its absence results in sterility.
The earliest symptoms of its deficiency are in the intestinal tract.
It is soluble in fat, but only slightly soluble in water. It is little affected by ordinary boiling or baking, but is destroyed by frying.
It is found in most concentrated amounts in all green leaves commonly used for salads, all green and yellow vegetables, such as broccoli, carrots, yellow or green squash, yellow corn, sweet potatoes, green beans and peas, asparagus, okra, tomatoes, avacadoes, cantaloupes, apricots, bananas, cherries, peaches, prunes, mangoes, olives and dates. Whole raw milk, cream, butter, nearly all fats, cheese, egg yolks, fish-oils, red salmon and oysters are also important sources of Vitamin A.