Fat-Soluble and Water-Soluble Vitamins: Characteristics, Functions, Deficiency, and Toxicity

Fat-Soluble and Water-Soluble Vitamins

Introduction to Vitamins

Vitamins are essential, noncaloric, organic nutrients required in small amounts to support vital cellular processes. They assist in the digestion, absorption, metabolism, and incorporation of macronutrients into bodily structures. Some vitamins exist as precursors, which are transformed into active forms within the body. Vitamins are classified into two main groups: fat-soluble and water-soluble.

• Fat-soluble vitamins: Vitamins A, D, E, and K

• Water-soluble vitamins: Vitamin C and B vitamins (thiamin, riboflavin, niacin, B6, folate, B12, pantothenic acid, biotin)

Capitalization Conventions

• Names of vitamins and minerals are not capitalized within sentences.

• Examples: vitamin D, biotin, iron

Characteristics of Fat-Soluble vs. Water-Soluble Vitamins

Characteristic	Fat-Soluble Vitamins (A, D, E, K)	Water-Soluble Vitamins (B Vitamins, C)
Absorption	Absorbed like fats, into lymph then blood	Absorbed directly into blood
Transport & Storage	Travel with protein carriers; stored in liver or fatty tissues	Travel freely in watery fluids; not stored in body
Excretion	Not readily excreted; tend to build up in tissues	Readily excreted in urine
Toxicity	Toxicities are likely from supplements, but occur rarely from food	Toxicities are unlikely but possible with high doses from supplements
Requirements	Needed in periodic doses (weeks/months) depending on extent of body stores	Needed frequently (even daily) because the body does not store most of them to any extent

Functional Groups of Vitamins and Minerals

Antioxidants

• Key antioxidant vitamins: beta-carotene, vitamin E, vitamin C

• Key antioxidant mineral: selenium

• Many antioxidant phytochemicals also exist in foods

Bone Health

• Key vitamins: vitamin D, vitamin K, vitamin C

• Key minerals: calcium, phosphorus, magnesium, fluoride

Energy Metabolism

• Key vitamins: thiamin, riboflavin, niacin, folate, B12, B6, biotin, pantothenic acid

• Key minerals: iodine, iron, magnesium, zinc, selenium, copper, chromium, manganese, sulfur, molybdenum

• Other nutrient: water

The Fat-Soluble Vitamins

General Properties

• Found in the fats and oils of foods (plant and animal)

• Do not need to be consumed every day due to storage in body tissues

• Excess intake can lead to toxic buildup in fatty tissues and organs

• Deficiency can result from low dietary intake, malabsorption, bariatric surgery, or excessive laxative use

Vitamin A

Types and Functions

• Precursor (plant-derived): beta-carotene (antioxidant)

• Active forms (animal-derived): retinol (stored in liver), retinal, retinoic acid

Role in Vision

• Maintains healthy cornea

• Involved in light perception at the retina

• Part of rhodopsin molecule; when light hits retina, vitamin A breaks off, sending signal to optic nerve

• Deficiency leads to night blindness (delayed recovery of vision in low light)

Consequences of Deficiency

• Xerophthalmia and blindness: keratinization of cornea, xerosis (dry eyes), permanent blindness

• Reduction of protein synthesis

• Essential for epithelial tissue: cell differentiation, vulnerability to infection, tissue dryness

• Immune system: regulates genes involved in immunity; deficiency leads to malnutrition and infection

• Reproduction and growth: sperm development, fetal organ development, bone growth in children

Toxicity

• Caused by excess supplements/fortified foods

• Symptoms: skin rash, hair loss, birth defects, bone abnormalities, liver failure, death

• High-risk groups: pregnant women (birth defects), children (supplement overdose)

Recommendations and Sources

• DRI: 900 μg/day (men), 700 μg/day (women)

• UL: 3,000 μg/day

• Richest sources: liver, fish, milk, eggs, fortified foods

Beta-Carotene

• Carotenoids: beta-carotene and relatives; found in orange and dark green vegetables

• Dietary antioxidant: protects against macular degeneration

• Toxicity: non-lethal, causes skin discoloration

• Sources: sweet potato, carrots, apricots, spinach, winter squash, cantaloupe, lettuce

Free-Radical Damage and Antioxidant Protection

• Free radicals cause chain reactions that damage cellular structures

• Antioxidants (e.g., vitamins A, C, E) quench free radicals and protect cells

• Oxidative stress is linked to aging, cancer, heart disease, diabetes

Example: Vitamin E and beta-carotene act as antioxidants to neutralize free radicals.

Vitamin D

General Properties

• Not an essential nutrient; synthesized in skin via sunlight

Primary Roles

• Calcium regulation: acts at skeleton (release), digestive tract (absorption), kidneys (retention)

• Hormone: affects genetic regulation of reproductive functions, hair follicles, immunity

• Research ongoing: cardiovascular disease, cancer, diabetes, autoimmune disorders

Deficiency

• Rickets: bowed legs, beaded ribs in children; prevented by sunlight, fortified milk, supplements

• Osteomalacia: soft, weak, deformed bones in adults

• Osteoporosis: brittle bones, prone to breaking

Toxicity

• Most potentially toxic vitamin

• Increases blood calcium (hypercalcemia), leading to kidney stones, heart failure, death

• Symptoms: nausea, fatigue, back pain, irregular heartbeat, increased urination, thirst

Vitamin D and Melanin

• Melanin acts as a natural sunscreen

• Darker skin requires more sunlight for vitamin D synthesis

• Balance sun exposure to avoid skin cancer risk

Risk Factors Affecting Vitamin D Synthesis

Factor	Effect on Vitamin D Synthesis
Advanced age	Skin loses capacity to synthesize vitamin D
Air pollution	Particles screen out sun's rays
City living	Tall buildings block sunlight
Clothing	Blocks sunlight
Cloudy skies	Reduces sunlight penetration
Geography	Insufficient exposure above 40° latitude in winter
Homebound	Living indoors prevents exposure
Season	Warmer seasons = more direct sun rays
Skin pigment	Darker skin needs more direct sun than lighter skin
Sunscreen	Reduces/prevents skin exposure to sun's rays
Time of day	Midday hours bring maximum direct sun exposure

Recommendations

• Ages 1-70: 15 μg/day (600 IU)

• 71+: 20 μg/day (800 IU)

• UL for adults: 10,000 μg/day

• Adequate calcium intake required for vitamin D to increase calcium levels

Food Sources

• Fortified milk and milk products (butter, cream)

• Fatty fish (salmon, tuna, mackerel, sardines)

• Fortified products (milk substitutes, orange juice, cereals, margarine)

• Egg yolks, liver, fatty meats

• Mushrooms (only when grown in sunlight)

Example: Fortified milk and exposure to sunlight are key for maintaining adequate vitamin D levels.

*Additional info: This guide covers only fat-soluble vitamins (A, D, E, K) in detail, as per the provided slides. Water-soluble vitamins are listed but not expanded upon in this excerpt. For a complete study, students should review water-soluble vitamins in further detail.*