Water-Soluble Vitamins

Overview

Water-soluble vitamins include vitamin C and the B vitamins. These vitamins dissolve in water, are easily excreted in urine, and are not stored in the body (with the exception of vitamin B12, which can remain in tissues for a month). They are sensitive to heat, light, and oxygen, which can destroy them during food processing.

• Not stored in the body: Regular intake is necessary to avoid deficiency.

• Destroyed by cooking and processing: Some are lost when exposed to light, heat, or oxygen.

Vitamin C (Ascorbic Acid)

Characteristics and Roles

Vitamin C, also known as ascorbic acid, is essential for connective tissue health and immune function.

• Collagen maintenance: Required for the formation and repair of connective tissues (bones, teeth, skin, tendons, scar tissue).

• Antioxidant: Protects iron and promotes its absorption; acts as a prooxidant outside the body, triggering reactions involving oxygen, iron, and copper.

• Immune support: Sufficient intake is important for white blood cell function.

Deficiency and Toxicity

• Scurvy: Caused by a drastic decrease in collagen synthesis. Symptoms include loss of appetite, growth cessation, tenderness, weakness, bleeding gums, loose teeth, swollen joints, and pinpoint red spots on the skin.

• At-risk groups: Smokers, people with limited food access, and those with alcohol or drug addiction.

• Toxicity: Safe intake range is 10–2,000 mg/day.

Recommendations and Food Sources

• Recommended intake: 90 mg/day for men, 75 mg/day for women; smokers require higher intake.

• Food sources: Fresh fruits and vegetables (citrus, peppers, broccoli, potatoes).

• Destruction: Heat and oxygen destroy vitamin C; eat cut or processed produce within a week.

The B Vitamins

Overview

The B vitamins include thiamin (B1), riboflavin (B2), niacin (B3), folate, B12, B6, biotin, and pantothenic acid. Deficiencies affect every cell in the body, but are rare due to the variety of nutrients in most diets.

• Signs and symptoms of deficiency: Nausea, exhaustion, irritability, depression, forgetfulness, loss of appetite, weight loss, muscle pain, immune impairment, abnormal heart action, skin problems, swollen tongue, cracked mouth corners, and eye issues.

Roles of B Vitamins

• Coenzymes: Activate enzymes for metabolic reactions.

• Energy metabolism: Help the body use carbohydrates, lipids, and amino acids for energy.

• Cell multiplication: Folate and B12 are essential for DNA synthesis and red blood cell formation.

Thiamin (B1)

Functions and Deficiency

• Role: Critical coenzyme in energy metabolism; important for nerve cell function.

• Deficiency: Beriberi (wet and dry forms) and Wernicke-Korsakoff syndrome (from alcohol abuse). Symptoms include apathy, irritability, confusion, memory loss, jerky eye movements, and a staggering gait.

• Toxicity: None reported.

Recommendations and Food Sources

• DRI: Men: 1.2 mg/day; Women: 1.1 mg/day.

• Food sources: Enriched pasta, pork chop, green peas, black beans, sunflower seeds.

Riboflavin (B2)

Functions and Deficiency

• Role: Coenzyme in energy metabolism.

• Deficiency: Cracks at mouth corners, sore throat, hypersensitivity to light.

• Destroyed by: Ultraviolet light and irradiation; milk is sold in opaque containers to prevent loss.

• Toxicity: None reported.

Recommendations and Food Sources

• DRI: Men: 1.3 mg/day; Women: 1.1 mg/day.

• Food sources: Milk, cottage cheese, beef liver, pork chop, enriched cereal, mushrooms.

Niacin (B3)

Functions and Deficiency

• Role: Coenzyme in energy metabolism; can be used to improve blood lipids.

• Deficiency: Pellagra (characterized by the "4 Ds": diarrhea, dermatitis, dementia, death).

• Toxicity: "Niacin flush" (skin tingling and redness), liver damage, impaired glucose tolerance.

Recommendations and Food Sources

• DRI: Men: 16 mg/day; Women: 14 mg/day.

• Food sources: Chicken breast, tuna, pork chop, enriched cereal, baked potato, mushrooms.

Folate

Roles and Deficiency Outcomes

• Role: DNA synthesis, metabolism of vitamin B12 and amino acids.

• Deficiency: Anemia, neural tube defects, diminished immunity, abnormal digestion, increased cancer risk.

• Highly interactive with medications: Antacids, aspirin, chemotherapy.

Prevention of Neural Tube Defects

• Consuming enough folate during pregnancy reduces risk of neural tube defects (NTD), cleft lip, and miscarriages.

• Folic acid fortification has reduced NTD prevalence in many countries.

Recommendations and Food Sources

• Folate enrichment: Absorbable synthetic form is folic acid.

• DRI: 400 mcg/day for adults.

• Food sources: Leafy green vegetables, beans, legumes, enriched flour products.

• Dietary folate equivalent (DFE): Converts all forms of folate to micrograms equivalent to food folate.

• Toxicity: UL is 1,000 mcg/day; may mask B12 deficiency.

Vitamin B12 (Cobalamin)

Functions and Deficiency

• Works with folate: Both needed for cell replication and activation.

• Maintains nerve sheaths: Protects nerve fibers for proper function.

• Deficiency: Anemia (large, immature red blood cells), nerve damage (creeping paralysis, impaired mental function).

Malabsorption and Food Sources

• Malabsorption causes: Low stomach acid, lack of intrinsic factor (pernicious anemia).

• Food sources: Only supplied by animal foods (meat, fish, eggs, milk); vegans need supplements or fortified foods.

Vitamin B6

Functions and Deficiency

• Role: Participates in over 100 reactions, including conversion of tryptophan to serotonin, synthesis of hemoglobin and neurotransmitters, maintenance of blood glucose, immune function, and fetal brain development.

• Deficiency: Weakness, depression, confusion, irritability, dermatitis.

• Toxicity: Effects seen with intake >2 g/day.

Recommendations and Food Sources

• DRI: Adults: 1.3 mg/day.

• Food sources: Beef liver, banana, baked potato, chicken breast, sweet potato, spinach.

Biotin

Key Roles and Food Sources

• Role: Coenzyme for carbohydrate, fat, and protein metabolism.

• Food sources: Legumes, egg yolks, organ meats, nuts, seeds, mushrooms, avocados, sweet potatoes, nutritional yeast.

• No UL set.

Pantothenic Acid

Key Roles and Food Sources

• Role: Key coenzyme for macronutrient metabolism; synthesis of lipids, neurotransmitters, steroid hormones, and hemoglobin.

• Food sources: Found in most foods; deficiency is very rare.

• No UL set.

Vitamin Supplements: Risks and Benefits

Considerations

• Increased needs: Certain life stages (menstruation, pregnancy, lactation, newborns) may require more nutrients.

• Impaired status: Appetite and physical stress (addiction, medication) can impair nutrient status.

• Food vs. supplements: Food rarely causes nutrient imbalances or toxicities; supplements may lead to excessive intake and contamination.

• Whole foods: Best for nutrient balance.

Supplements and Chronic Disease

• Vitamin D and cancer: No evidence for prevention.

• Antioxidant supplements: No evidence for prevention of chronic diseases.

• Vitamin E: No observed benefit or harm.

• Beta-carotene: Increased lung cancer risk in smokers with supplementation.

Choosing the Right Supplement

• Avoid marketing traps: Ignore claims of "immunity," "weight loss," "increased energy," "mega-dose," etc.

• Evaluate structure-function claims.

• Read labels: Target your needs, choose appropriate doses, and avoid exceeding the UL.

• Choose correct formula: For age and sex; avoid >10 mg iron except for menstruating women.

• Look for third-party verification: NSF, USP, Consumer Lab.

Tables

Effect of Folic Acid Fortification on Neural Tube Defects

Summary Table: Water-Soluble Vitamins

Additional info: All equations and metabolic pathways referenced are based on standard biochemistry, e.g., energy metabolism involves the conversion of macronutrients to ATP via coenzyme-dependent reactions.