Nutrient Deficiency Diseases

Why This Matters

Nutrient deficiency diseases aren't just historical curiosities—they're living proof of how specific nutrients function in your body. When you study scurvy, you're really learning about collagen synthesis; when you examine goiter, you're understanding thyroid hormone regulation. These diseases demonstrate the consequences of disrupting essential biochemical pathways, and that's exactly what you're being tested on in nutrition courses.

The key to mastering this topic is recognizing the patterns: fat-soluble vitamin deficiencies often affect bones and vision, B-vitamin deficiencies typically impact energy metabolism and the nervous system, and mineral deficiencies disrupt everything from oxygen transport to hormone production. Don't just memorize disease names—know which nutrient is missing, what physiological process it disrupts, and who's most at risk.

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Fat-Soluble Vitamin Deficiencies

Fat-soluble vitamins (A, D, E, K) require dietary fat for absorption and are stored in body tissues. Deficiencies develop slowly but can cause lasting structural damage, particularly to bones, eyes, and skin.

Vitamin A Deficiency (Night Blindness, Xerophthalmia)

• Night blindness is the earliest clinical sign—vitamin A is essential for rhodopsin production in retinal rod cells
• Xerophthalmia (drying and thickening of the conjunctiva) can progress to corneal ulceration and permanent blindness
• Immune function suffers significantly—vitamin A maintains epithelial barriers and supports white blood cell activity

Vitamin D Deficiency (Rickets, Osteomalacia)

• Rickets in children vs. osteomalacia in adults—same deficiency, different manifestations based on whether bones are still growing
• Calcium absorption drops dramatically without adequate vitamin D, leading to soft, weak bones prone to deformity
• Limited sun exposure is a major risk factor—darker skin, northern latitudes, and indoor lifestyles all increase deficiency risk

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Water-Soluble Vitamin Deficiencies: B-Complex

B vitamins function as coenzymes in energy metabolism and nervous system function. Because they're water-soluble and not stored long-term, deficiencies can develop within weeks of inadequate intake.

Beriberi (Thiamine/Vitamin B1 Deficiency)

• "Wet" beriberi affects the heart; "dry" beriberi affects the nerves—thiamine is critical for glucose metabolism in high-energy tissues
• Polished white rice diets are the classic cause—milling removes the thiamine-rich bran layer
• Wernicke-Korsakoff syndrome is the severe neurological form seen in chronic alcoholics due to impaired thiamine absorption

Pellagra (Niacin/Vitamin B3 Deficiency)

• The "4 D's": dermatitis, diarrhea, dementia, and death—a classic exam mnemonic for identifying pellagra
• Corn-based diets are historically linked because corn contains niacin in a bound form (niacytin) that humans can't absorb
• Tryptophan can be converted to niacin—so adequate protein intake provides a secondary source

Vitamin B12 Deficiency (Pernicious Anemia)

• Pernicious anemia results from lack of intrinsic factor, not just dietary deficiency—the stomach must produce this protein for B12 absorption
• Neurological damage can be irreversible—B12 is essential for myelin sheath maintenance; numbness and cognitive changes are warning signs
• Vegans and older adults are high-risk groups—B12 is found only in animal products, and absorption efficiency declines with age

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Water-Soluble Vitamin Deficiencies: Vitamin C

Unlike most animals, humans cannot synthesize vitamin C and must obtain it from diet. This makes scurvy a uniquely human vulnerability with significant historical importance.

Scurvy (Vitamin C Deficiency)

• Collagen synthesis fails without vitamin C—this explains the bleeding gums, poor wound healing, and joint pain
• Symptoms appear after 1-3 months of deficiency—the body's vitamin C stores are limited but not immediately depleted
• Historical significance in maritime exploration—scurvy killed more sailors than combat; citrus fruits ("limeys") were the cure

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Mineral Deficiencies

Minerals serve as structural components and enzyme cofactors throughout the body. Deficiency patterns often reflect geographic, dietary, or physiological factors affecting intake or absorption.

Iron Deficiency Anemia

• Most common nutritional deficiency worldwide—iron is essential for hemoglobin synthesis and oxygen transport
• Microcytic, hypochromic red blood cells (small and pale) are the diagnostic hallmark on blood smears
• Women of reproductive age and growing children are highest-risk groups due to menstrual losses and rapid tissue growth

Iodine Deficiency Disorders (Goiter)

• Goiter is the thyroid's attempt to compensate—without iodine, the gland enlarges trying to capture more from the bloodstream
• Cretinism in children causes irreversible intellectual disability—iodine is critical for brain development during pregnancy and infancy
• Iodized salt programs have nearly eliminated goiter in developed countries—a major public health success story

Zinc Deficiency

• Growth retardation and delayed sexual maturation are hallmark signs in children and adolescents
• Impaired wound healing and immune dysfunction—zinc is a cofactor for over 300 enzymes involved in cell division and repair
• Phytates in plant foods reduce zinc absorption—vegetarians may need 50% more dietary zinc than omnivores

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Protein-Energy Malnutrition

These severe deficiency states result from inadequate macronutrient intake and represent the most life-threatening forms of malnutrition. Understanding the distinction between kwashiorkor and marasmus is a classic exam topic.

Kwashiorkor

• Edema (fluid retention) is the distinguishing feature—low serum albumin causes fluid to leak from blood vessels into tissues
• "Flaky paint" dermatitis and reddish hair discoloration result from impaired protein synthesis affecting skin and hair
• Occurs with adequate calories but insufficient protein—often seen when children are weaned onto starchy, low-protein foods

Marasmus

• Severe wasting with no edema—the body catabolizes its own muscle and fat stores for energy
• "Old man's face" appearance due to loss of subcutaneous fat, even in infants
• Results from overall energy and protein deficiency—essentially starvation affecting all macronutrients

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Quick Reference Table

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Self-Check Questions

1. Which two deficiency diseases are both caused by B-vitamins and historically associated with populations dependent on single grain staples? What distinguishes their symptoms?

2. A patient presents with edema, skin lesions, and an enlarged liver but is not severely underweight. Which form of protein-energy malnutrition is this, and what dietary pattern likely caused it?

3. Compare and contrast rickets and osteomalacia—what do they share, and why do they present differently?

4. If an FRQ asks you to explain why vegans are at risk for certain deficiencies but not others, which nutrients would you discuss and why?

5. Both iron and iodine deficiencies have been addressed through food fortification programs. Identify the fortification strategy for each and explain why these minerals were prioritized for public health intervention.