Chapter 10. Nutritional Diseases

Essential Nutrients

An adequate diet must provide sufficient total proteins, sufficient total calories, essential amino acids, essential fatty acids, vitamins, and minerals. A deficiency of any of these dietary factors leads to disordered cellular metabolism and cellular injury with recognizable symptoms and signs of nutritional deficiency. Nutritional diseases arising from total protein-energy deficiency and various vitamin and mineral deficiencies are well-recognized (Table 10-1).

Table 10–1. Principal Human Nutrients and Disorders Resulting from Nutritional Deficiency or Excess.

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Table 10–1. Principal Human Nutrients and Disorders Resulting from Nutritional Deficiency or Excess.

Nutrient

Physiologic Importance

Deficiency

Excess

Protein

Numerous.

Marasmus; kwashiorkor; growth retardation.

None.

Calories

Numerous.

Marasmus; kwashiorkor; growth retardation.

Obesity.

Fat-soluble vitamins 1

Vitamin A

Retinol is constituent of retinal rod pigment rhodopsin. Maintain epithelia.

Loss of night vision; increased thickness of squamous epithelia; Bitot's spots; xerophthalmia, keratomalacia (eyes); follicular hyperkeratosis (skin).

Bleeding; hepatosplenomegaly 2 (rare).

Vitamin D (cholecalciferol)

1,25-Dihydroxycholecalciferol activates calcium absorption in intestine and causes bone mineralization.

Rickets (children); osteomalacia (adults).

Hypercalcemia leading to metastatic calcification and renal damage 2 (rare).

Vitamin K

Required for synthesis of prothrombin and clotting factors, VII, IX, and X.

Hypoprothrombinemia resulting in bleeding tendency.

Hemolytic anemia 2 (rare).

Water-soluble vitamins 1

Vitamin C (ascorbic acid)

Required for synthesis of collagen and osteoid.

Scurvy; impaired wound healing.

Minimal—possibly urinary calculi.

Thiamine (vitamin B 1 )

Coenzyme in decarboxylase systems; required for synthesis of acetylcholine.

Beriberi (wet and dry); Wernicke's encephalopathy; Korsakoff's syndrome.

Transient flushing, dizziness.

Riboflavin (vitamin B 2 )

Constituent of flavoproteins.

Cheilosis, glossitis, angular stomatitis; corneal vascularization.

None.

Niacin

Constituent of NAD and NADP.

Pellagra.

Flushing due to vasodilation occurs with intravenous injection (rare).

Pyridoxine (vitamin B 6 )

Coenzyme for decarboxylase and transaminase systems.

Glossitis; blepharitis; dermatitis; cheilosis; peripheral neuropathy; sideroblastic anemia.

Transient paresthesias.

Folic acid

Required for nucleic acid synthesis.

Megaloblastic anemia.

None.

Vitamin B 12

Required for nucleic acid synthesis.

Megaloblastic anemia; subacute combined degeneration of spinal cord; peripheral neuropathy.

None.

Minerals

Iron

Constituent of hemoglobin and myoglobin.

Hypochromic anemia; loss of mucosal integrity.

Hemochromatosis.

1 The fat-soluble vitamins are present especially in fatty foods (milk, butter, etc) and may be deficient when there is fat malabsorption for any reason. Water-soluble vitamins are widely distributed in fruits, vegetables, and animal products, with the exception of vitamin B 12 , which is found almost exclusively in meat. Water-soluble vitamins are less affected by generalized malabsorption states; specific malabsorption of vitamin B 12 occurs in pernicious anemia.

2 Note that excess amounts of fat-soluble vitamins accumulate in body fat stores and may lead to toxicity; toxicity of water-soluble vitamins is much rarer, probably because of rapid excretion of any excess in the urine.