Food and Nutrition Science — Vitamins, Minerals, Hydration, and Health

Vitamins: An Overview

Definition of a vitamin:

Needed only in trace amounts but cannot be synthesized in the body
An organic nutrient that must be obtained from food

Classifying vitamins:

Fat-soluble vitamins (A, D, E, K):

Absorbed together with fat
Can be stored in the liver and fat tissue
Risk of toxicity with excess intake (especially A and D)
No need for daily intake

Water-soluble vitamins (C, B vitamins):

Dissolve in water
Excreted in urine when in excess
Not stored → must be consumed daily
Low risk of toxicity

Fat-Soluble Vitamins

Vitamin A (retinol):

Function: vision (prevents night blindness), immunity, cell differentiation, skin health
Deficiency: night blindness, dry eyes, weakened immunity
Food sources: liver, carrots, sweet potato, spinach (beta-carotene → A)
Excess: toxicity (headache, nausea, liver damage)

Vitamin D (calciferol):

Function: promotes calcium and phosphorus absorption, forms bones and teeth
Deficiency: rickets (children), osteomalacia (adults), osteoporosis
Food sources: fish oil, egg yolk, fortified milk
Synthesized in the body: made in skin exposed to sunlight (UV)
Deficiency risk in modern life: indoor living, sun avoidance

Vitamin E (tocopherol):

Function: antioxidant (protects cell membranes), boosts immunity
Deficiency: rare, but can cause hemolytic anemia
Food sources: vegetable oil, nuts, seeds, green vegetables

Vitamin K:

Function: blood clotting, bone metabolism
Deficiency: increased bleeding tendency
Food sources: leafy greens, fermented foods
Caution: those on anticoagulants (warfarin) should watch their intake

Water-Soluble Vitamins

Vitamin C (ascorbic acid):

Function:
- antioxidant (removes free radicals)
- collagen synthesis (maintains skin, vessels, and bone)
- promotes iron absorption
- boosts immunity
Deficiency: scurvy (bleeding gums, joint pain, skin bleeding)
Food sources: citrus fruit, strawberries, kiwi, bell peppers, broccoli
Heat-sensitive → best consumed raw for efficiency

B vitamins:

Act as coenzymes in energy metabolism

Vitamin B1 (thiamine):

Carbohydrate metabolism → energy production
Deficiency: beriberi (nerve and muscle disorder)

Vitamin B2 (riboflavin):

Energy metabolism, maintains skin and mucous membranes
Deficiency: angular cheilitis, glossitis

Vitamin B12:

Nerve function, DNA synthesis, red-blood-cell formation
Deficiency: pernicious anemia, nerve damage
Found only in animal foods → a risk for vegans
Requires intrinsic factor (IF) for absorption

Folate (vitamin B9):

DNA synthesis, cell division
Essential during pregnancy: prevents neural-tube defects
Deficiency: megaloblastic anemia
Food sources: green vegetables, legumes, liver

Minerals

Classifying minerals:

Macrominerals: needed at over 100mg/day (Ca, P, Mg, Na, K, Cl)
Trace minerals: needed at under 100mg/day (Fe, Zn, I, Se, Cu, F)

Calcium (Ca):

Function: bone and tooth structure (99%), muscle contraction, signal transmission, blood clotting
Deficiency: osteoporosis, muscle cramps
Absorption boosted by: vitamin D, lactose
Absorption blocked by: excess phosphorus, phytic acid (in grains)
Food sources: dairy, small fish eaten with bones, tofu, green vegetables

Iron (Fe):

Function: hemoglobin (oxygen transport), myoglobin, enzymes
Deficiency: iron-deficiency anemia (the most common nutrient deficiency)
Heme iron (meat): 15–35% absorption
Non-heme iron (plant-based): 2–20% absorption (lower)
Absorption improves when consumed with vitamin C
At-risk groups: women of reproductive age, pregnant women, vegans

Sodium (Na):

Function: the main extracellular cation, osmotic-pressure regulation, nerve signaling
Excess: hypertension, edema, cardiovascular risk
South Korea’s average intake: more than twice the recommended level (from soups, stews, and kimchi)
Intake goal: under 2,000mg/day

Water and Health

Body water:

About 60% of body weight (men), 50% (women)
More abundant in muscle tissue, less in fat tissue

Functions of water:

Transports nutrients and waste
Regulates body temperature (sweating)
Lubricates joints
Mediates chemical reactions
Maintains blood pressure

Water intake and loss:

Intake: beverages, food, metabolic water
Loss: urine (the largest share), sweat, respiration, feces

The effects of dehydration:

1–2% of body weight: thirst, reduced concentration
4–5% of body weight: headache, fatigue, reduced muscle strength
7–10%+ of body weight: heatstroke, risk of death

Daily water requirement:

Adults: about 2–2.5L (food + beverages)
Extra needed during exercise or hot weather
Urine color: pale yellow indicates adequate hydration

Water-electrolyte balance:

Electrolytes: Na⁺, K⁺, Cl⁻, HCO₃⁻
Vomiting or diarrhea: causes electrolyte imbalance → use sports drinks or oral rehydration solution
Excessive water intake: risk of hyponatremia (rare but potentially fatal)

South Korea’s Dietary Reference Intakes

Dietary reference intakes (DRIs):

Estimated Average Requirement (EAR):

The amount that meets the needs of 50% of a population

Recommended Nutrient Intake (RNI):

The amount that meets the needs of 97–98% of a population (EAR + 2SD)

Adequate Intake (AI):

Estimated from observation when experimental evidence is insufficient

Tolerable Upper Intake Level (UL):

The maximum intake without risk of adverse health effects

Acceptable macronutrient distribution range:

Carbohydrates: 55–65%
Protein: 7–20%
Fat: 15–30%

Nutrients of concern for South Koreans:

Vitamin D: high risk of deficiency
Calcium: intake falls short of recommended levels
Sodium: excessive intake
Dietary fiber: insufficient (recommended: 25–30g/day)
Iron: deficiency risk for women of reproductive age

Nutrition-label standards:

Check the %DV (percent of the daily value)
Lower is better for saturated fat and sodium
Higher is better for fiber, vitamins, and minerals

Frequently Asked Questions

Q. Can vitamin supplements replace vitamins from food? A. Supplements are useful for concentrated intake of a specific nutrient but are difficult to substitute fully for food. Food contains not just vitamins but also fiber, phytochemicals (polyphenols, carotenoids, and the like), and other micronutrients whose interactions matter. Unless a deficiency has been confirmed or a special circumstance applies — pregnancy, a vegan diet, and similar cases — the general rule is to obtain nutrients from a varied diet.

Q. Why is traditional Korean food often high in sodium? A. Traditional Korean cuisine has a well-developed culture of soy sauce, soybean paste, chili paste, salt-cured foods (kimchi, pickled vegetables), and soups and stews, which raises sodium content. Fermented foods are nutritionally beneficial but tend to be high in sodium. To cut sodium intake, eating less broth, using reduced-sodium soy sauce, and eating more vegetables (potassium promotes sodium excretion) all help.