https://www.britannica.com/science/nutritional-disease
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Although deficiency diseases have been described in laboratory animals and humans deprived of single vitamins, in human experience multiple deficiencies are usually present simultaneously. The eight B-complex vitamins function in coordination in numerous enzyme systems and metabolic pathways; thus, a deficiency of one may affect the functioning of others.
Vitamin A
Vitamin A deficiency is the leading cause of preventable blindness in children and is a major problem in the developing world, especially in Africa and Southeast Asia; in the poorest countries hundreds of thousands of children become blind each year due to a deficiency of the vitamin. Even a mild deficiency can impair immune function, thereby reducing resistance to disease. Night blindness is an early sign of vitamin A deficiency, followed by abnormal dryness of the eye and ultimately scarring of the cornea, a condition known as xerophthalmia. Other symptoms include dry skin, hardening of epithelial cells elsewhere in the body (such as mucous membranes), and impaired growth and development.
Vitamin D
Vitamin D (also known as vitamin D hormone) is synthesized in the body in a series of steps, starting in the skin by the action of sunlight’s ultraviolet rays on a precursor compound; thus, without adequate food sources of vitamin D, a deficiency of the vitamin can occur when exposure to sunlight is limited. Lack of vitamin D in children causes rickets, a disease characterized by inadequate mineralization of bone, growth retardation, and skeletal deformities such as bowed legs. The adult form of rickets, known as osteomalacia, results in weak muscles as well as weak bones. Inadequate vitamin D may also contribute to the thinning of bones seen in osteoporosis. Individuals with limited sun exposure (including women who completely cover their bodies for religious reasons), elderly or homebound persons, and those with dark skin, particularly those who live in northern latitudes, are at risk of vitamin D deficiency. Vitamin D is found in very few foods naturally; thus fortification of milk and other foods (e.g., margarine, cereals, and breads) with the vitamin has helped protect those populations in which sun exposure is inadequate. Supplemental vitamin D also may help protect against bone fractures in the elderly, who make and activate vitamin D less efficiently even if exposed to sunlight.
Vitamin E
Vitamin E deficiency is rare in humans, although it may develop in premature infants and in people with impaired fat absorption or metabolism. In the former, fragility of red blood cells (hemolysis) is seen; in the latter, where deficiency is more prolonged, neuromuscular dysfunction involving the spinal cord and retina may result in loss of reflexes, impaired balance and coordination, muscle weakness, and visual disturbances. No specific metabolic function has been established for vitamin E; however, it is an important part of the antioxidant system that inhibits lipid peroxidation—i.e., it protects cells and their membranes against the damaging effects of free radicals that are produced metabolically or enter the body from the environment. The requirement for vitamin E is increased with increasing consumption of polyunsaturated fatty acids. People who smoke or are subjected to air pollution may also need more of the vitamin to protect against oxidative damage to the lungs.
Vitamin K
Vitamin K is necessary for the formation of prothrombin and other blood-clotting factors in the liver, and it also plays a role in bone metabolism. A form of the vitamin is produced by bacteria in the colon and can be utilized to some degree. Vitamin K deficiency causes impaired clotting of the blood and internal bleeding, even without injury. Due to poor transport of vitamin K across the placenta, newborn infants in developed countries are routinely given the vitamin intramuscularly or orally within six hours of birth to protect against a condition known as hemorrhagic disease of the newborn. Vitamin K deficiency is rare in adults, except in syndromes with poor fat absorption, in liver disease, or during treatment with certain anticoagulant drugs, which interfere with vitamin K metabolism. Bleeding due to vitamin K deficiency may be seen in patients whose gut bacteria have been killed by antibiotics.
Thiamin
Prolonged deficiency of thiamin (vitamin B1) results in beriberi, a disease that has been endemic in populations where white rice has been the staple. Thiamin deficiency is still seen in areas where white rice or flour constitutes the bulk of the diet and thiamin lost in milling is not replaced through enrichment. Symptoms of the form known as dry beriberi include loss of appetite, confusion and other mental symptoms, muscle weakness, painful calf muscles, poor coordination, tingling and paralysis. In wet beriberi there is edema and the possibility of an enlarged heart and heart failure. In the developed world, thiamin deficiency is linked primarily to chronic alcoholism with poor diet, manifesting as Wernicke-Korsakoff syndrome, a condition with rapid eye movements, loss of muscle coordination, mental confusion, and memory loss.
Riboflavin
Riboflavin (vitamin B2) deficiency, known as ariboflavinosis, is unlikely without the simultaneous deficiency of other nutrients. After several months of riboflavin deprivation, symptoms include cracks in the skin at the corners of the mouth, fissures of the lips, and an inflamed, magenta-coloured tongue. Because riboflavin is readily destroyed by ultraviolet light, jaundiced infants who are treated with light therapy are administered the vitamin. Milk, milk products, and cereals, major sources of riboflavin in the diet, are packaged to prevent exposure to light.
Niacin
Symptoms of pellagra develop about two months after niacin is withdrawn from the diet. Pellagra is characterized by the so-called three Ds—diarrhea, dermatitis, and dementia—and, if it is allowed to progress untreated, death ensues. Pellagra was common in areas of the southern United States in the early 1900s and still occurs in parts of India, China, and Africa, affecting people who subsist primarily on corn. The niacin in corn and other cereal grains is largely in bound form, unable to be absorbed well. Sufficient high-quality protein (containing tryptophan) in the diet can protect against niacin deficiency even if intake of niacin itself is inadequate.
Vitamin B6
Vitamin B6 (pyridoxine and related compounds) is essential in protein metabolism, the synthesis of neurotransmitters, and other critical functions in the body. Deficiency symptoms include dermatitis, microcytic hypochromic anemia (small, pale red blood cells), impaired immune function, depression, confusion, and convulsions. Although full-blown vitamin B6 deficiency is rare, marginal inadequacy is more widespread, especially among the elderly, who may have a reduced ability to absorb the vitamin. People with alcoholism, especially those with the liver diseases cirrhosis and hepatitis, are at risk of deficiency.
Folic acid
Vitamin B12 and folic acid (folate) are two B vitamins with many closely related functions, notably participation in DNA synthesis. As a result, people with deficiencies of either vitamin show many of the same symptoms, such as weakness and fatigue due to megaloblastic anemia, a condition in which red blood cells, lacking sufficient DNA for cell division, are large and immature. Deficiency of folic acid also causes disruption of cell division along the gastrointestinal tract, which results in persistent diarrhea, and impaired synthesis of white blood cells and platelets. Inadequate intake of the vitamin in early pregnancy may cause neural tube defects in the fetus. Thus, women capable of becoming pregnant are advised to take 400 micrograms (μg) of folic acid daily from supplements, fortified foods (such as fortified cereals), or both—in addition to consuming foods rich in folic acid such as fresh fruits and vegetables (especially leafy greens) and legumes. Folic acid deficiency may also result from heavy use of alcohol, which interferes with absorption of the vitamin.
Vitamin B12
Deficiency of vitamin B12 (cobalamin), like folic acid, results in megaloblastic anemia (large, immature red blood cells), due to interference with normal DNA synthesis. Additionally, vitamin B12 maintains the myelin sheath that protects nerve fibres; therefore, an untreated deficiency of the vitamin can result in nerve degeneration and eventually paralysis. Large amounts of folic acid (over 1,000 μg per day) may conceal, and possibly even exacerbate, an underlying vitamin B12 deficiency. Symptoms of vitamin B12 deficiency can include weakness, fatigue, pain, shortness of breath, numbness or tingling sensations, mental changes, and vision problems. Only animal foods are reliable sources of vitamin B12. Vegans, who eat no foods of animal origin, are at risk of vitamin B12 deficiency and must obtain the vitamin through fortified food or a supplement. For people who regularly eat animal products, deficiency of the vitamin is unlikely, unless there is a defect in absorption. In order to be absorbed, vitamin B12 must be bound to intrinsic factor, a substance secreted by the stomach. If intrinsic factor is absent (due to an autoimmune disorder known as pernicious anemia) or if there is insufficient production of hydrochloric acid by the stomach, absorption of the vitamin will be limited.
Pantothenic acid
Pantothenic acid is so widespread in foods that deficiency is unlikely under normal circumstances. Deficiency has been seen only in individuals fed semisynthetic diets deficient in the vitamin or in subjects given a pantothenic acid antagonist. Symptoms of deficiency include fatigue, irritability, sleep disturbances, abdominal distress, and neurological symptoms such as tingling in the hands.
Biotin
Deficiency of biotin is rare, and this may be due in part to synthesis of the vitamin by bacteria in the colon, although the importance of this source is unclear. Biotin deficiency has been observed in people who regularly eat large quantities of raw egg white, which contains a glycoprotein (avidin) that binds biotin and prevents its absorption. A rare genetic defect that renders some infants unable to absorb a form of biotin in food can be treated with a supplement of the vitamin. Long-term use of certain anticonvulsant drugs may also impair biotin absorption. Symptoms of deficiency include skin rash, hair loss, and eventually neurological abnormalities.
Vitamin C
Vitamin C, also known as ascorbic acid, functions as a water-soluble antioxidant and as a cofactor in various enzyme systems, such as those involved in the synthesis of connective tissue components and neurotransmitters. Symptoms of scurvy, a disease caused by vitamin C deficiency, include pinpoint hemorrhages (petechiae) under the skin, bleeding gums, joint pain, and impaired wound healing. Although rare in developed countries, scurvy is seen occasionally in people consuming restricted diets, particularly those containing few fruits and vegetables, or in infants fed boiled cow’s milk and no source of vitamin C. Scurvy can be prevented with relatively small quantities of vitamin C (10 milligrams [mg] per day). Disease states, environmental toxins, drugs, and other stresses can increase an individual’s vitamin C needs.
Iron
Iron deficiency is the most common of all nutritional deficiencies, with much of the world’s population being deficient in the mineral to some degree. Young children and premenopausal women are the most vulnerabl. The main function of iron is in the formation of hemoglobin, the red pigment of the blood that carries oxygen from the lungs to other tissues. Since each millilitre of blood contains 0.5 mg of iron (as a component of hemoglobin), bleeding can drain the body’s iron reserves. When iron stores are depleted a condition arises known as microcytic hypochromic anemia, characterized by small red blood cells that contain less hemoglobin than normal. Symptoms of severe iron deficiency anemia include fatigue, weakness, apathy, pale skin, difficulty breathing on exertion, and low resistance to cold temperatures. Severe anemia increases the risk of pregnancy complications and maternal death. Iron deficiency anemia is most common during late infancy and early childhood, when iron stores present from birth are exhausted and milk, which is poor in iron, is a primary food; during the adolescent growth spurt; and in women during the childbearing years, because of blood loss during menstruation and the additional iron needs of pregnancy. Intestinal blood loss and subsequent iron deficiency anemia in adults may also stem from ulcers, hemorrhoids, tumours, or chronic use of certain drugs such as aspirin.
Iodine
Iodine deficiency disorders are the most common cause of preventable brain damage, which affects an estimated 50 million people worldwide. During pregnancy, severe iodine deficiency may impair fetal development, resulting in cretinism (irreversible mental retardation with short stature and developmental abnormalities) as well as in miscarriage and stillbirth. Other more pervasive consequences of chronic iodine deficiency include lesser cognitive and neuromuscular deficits. In chronic iodine deficiency the thyroid gland enlarges as it attempts to trap more iodide (the form in which iodine functions in the body) from the blood for synthesis of thyroid hormones, and it eventually becomes a visible lump at the front of the neck known as a goitre. Some foods, such as cassava, millet, sweet potato, certain beans, and members of the cabbage family, contain substances known as goitrogens that interfere with thyroid hormone synthesis; these substances, which are destroyed by cooking, can be a significant factor in persons with coexisting iodine deficiency who rely on goitrogenic foods as staples. Since a strategy of universal iodization of salt was adopted in 1993, there has been remarkable progress in improving iodine status worldwide.
Zinc
A constituent of numerous enzymes, zinc plays a structural role in proteins and regulates gene expression. Zinc deficiency in humans was first reported in the 1960s in Egypt and Iran, where children and adolescent boys with stunted growth and undeveloped genitalia responded to treatment with zinc. Deficiency of the mineral was attributed to the regional diet, which was low in meat and high in legumes, unleavened breads, and whole-grain foods that contain fibre, phytic acid, and other factors that inhibit zinc absorption. Symptoms of zinc deficiency may include skin lesions, diarrhea, increased susceptibility to infections, night blindness, reduced taste and smell acuity, poor appetite, hair loss, slow wound healing, low sperm count, and impotence. Zinc is highest in protein-rich foods, especially red meat and shellfish, and zinc status may be low in protein-energy malnutrition.
Calcium
Almost all the calcium in the body is in the bones and teeth, the skeleton serving as a reservoir for calcium needed in the blood and elsewhere. During childhood and adolescence, adequate calcium intake is critical for bone growth and calcification. A low calcium intake during childhood, and especially during the adolescent growth spurt, may predispose one to osteoporosis, a disease characterized by reduced bone mass, later in life. As bones lose density, they become fragile and unable to withstand ordinary strains; the resulting fractures, particularly of the hip, may cause incapacitation and even death. Osteoporosis is particularly common in postmenopausal women in industrial societies. Not a calcium-deficiency disease per se, osteoporosis is strongly influenced by heredity; risk of the disease can be lessened by ensuring adequate calcium intake throughout life and engaging in regular weight-bearing exercise.
Sodium
Sodium is usually provided in ample amounts by food, even without added table salt (sodium chloride). Furthermore, the body’s sodium-conservation mechanisms are highly developed, and thus sodium deficiency is rare, even for those on low-sodium diets. Sodium depletion may occur during prolonged heavy sweating, vomiting, or diarrhea or in the case of kidney disease. Symptoms of hyponatremia, or low blood sodium, include muscle cramps, nausea, dizziness, weakness, and eventually shock and coma. After prolonged high-intensity exertion in the heat, sodium balance can be restored by drinking beverages containing sodium and glucose (so-called sports drinks) and by eating salted food. Drinking a litre of water containing two millilitres (one-third teaspoon) of table salt also should suffice. Chloride is lost from the body under conditions that parallel those of sodium loss. Severe chloride depletion results in a condition known as metabolic alkalosis (excess alkalinity in body fluids).
Potassium
Potassium is widely distributed in foods and is rarely deficient in the diet. However, some diuretics used in the treatment of hypertension deplete potassium. The mineral is also lost during sustained vomiting or diarrhea or with chronic use of laxatives. Symptoms of potassium deficiency include weakness, loss of appetite, muscle cramps, and confusion. Severe hypokalemia (low blood potassium) may result in cardiac arrhythmias. Potassium-rich foods, such as bananas or oranges, can help replace losses of the mineral, as can potassium chloride supplements, which should be taken only under medical supervision.
