NUTR 400 4.3 Fat Soluble Vitamins

Properties of Fat Soluble Vitamins

Vitamins A, D, E, and K

• small amounts are needed for good health 

• Dissolves in lipid

• stored in adipose tissue and the liver

• can be toxic in high amounts

• in the “fatty” potion of foods 

• leaves the SI via chylomicrons 

• absorbed in the small intestine 

• deficiencies take longer (compared to water soluble) to appear because we have so much storage space 

Primary functions of Fat-soluble vitamins?

Vit A: vision and cell differentiation; functions as a hormone 

Vit D: Bone growth/maintenance, cell development/immunity'; functions as a hormone 

Vit E: Antioxidant 

Vit K: Blood Clotting and bone formation 

Vitamin A: A group of fat-soluble compounds

• Retinoids:

  • the active form of vit A (preformed)

  • Retinol (The only one in our diet)

  • Retinal 

  • Retinoic Acid 

• Carotenoids 

  • Has vitamin activity after conversion to active form in the body (provitamins) 

  • Beta-carotene – primary carotenoid in our diet

Carotenoids

• Fat soluble plant pigments

• SOME can be converted to Vit A (pro vit A)

• Most common ones:

  • Provitamin A carotenoids:

    • β-carotene (most abundant vitamin A provitamin)

    α-carotene

    • β-cryptoxanthin 

  • lutein, zeaxanthin, lycopene

Conversion of Vitamin A Compounds

Carotenoids (provitamin A) → converted in intestine → Retinol (active, storage form) → Retinal (vision) → Retinoic Acid (gene regulation).

• Provitamin A: plant-based (beta-carotene)

• Preformed vitamin A: animal-based (retinol)

• Retinol = storage + transport

• Retinal = vision use

• Retinoic acid = gene expression (cannot go backward!)

Dietary Sources of Vit A

• 40% of the US consume under the RDA

• 2/3 of Vit A is consumed as preformed vitamins (Retinol aka already active Vit A)

• Preformed: Highest in livers! So animal products like:

  • Liver

  • Eggs

  • Dairy (milk, cheese, butter)

  • Fish (especially oily fish)

• Provitamins:

  • plants! (yellow/orange/red veggies and fruit) 

  • dark leafy greens

**CAROTENOIDS ARE LESS BIOAVAILABLE THEN RETINOIDS

Functions of Vitamin A 

• Vision

• antioxidant capacity (Carotenoids) 

• functions as a hormone in:

  • Cell development

  • immune function

  • growth

  • bone health

  • reproduction

• Helps to maintain a healthy body lining (epithelial cells) without Vit A these cells would remain immature and wouldn’t form a solid barrier for the body

Vitamin A in light detection (Vision)

• retinal is a key component of rhodopsin! 

• Rhodopsin-

  • Detects the light in our eyes

  • The visual pigment that is formed when cis-retinal binds to Opsin (a protien) 

• Vit A helps convert the light into nerve impulses, which tell the brain what we’re seeing! 

• The rods in our retina allow us to see in low light

Vitamin A Deficiency: Night Blindness

• in a dark room, you can make out shapes. Then a flash of bright light blinds you, as the pigment in the retina is bleached! Your eyes adjust! Without Vit A, this process takes much longer

• After this- the production of mucus in our tears will DEC, drying the cornea of our eyes! This can cause blindness

• The leading cause of blindness in kids world wide!

Do Carotenoids act as antioxidants?

YES! they help to protect from free radicals!

Vitamin A Deficiency: Hypovitaminosis A

• when you have little preformed Vit A!

• • Night blindness

  • Permanent blindness

  • Impaired immunity

  • Rough, dry, or scaly skin (from the lack of mucus)

  • Keratinization (our epithelial cells cannot form properly, and are full of keratin!)

Vitamin A Toxicity!

• When a large dose of preformed Vit A is consumed!

• Complications:

  • Blurred vision

  • liver abnormalities

  • reduced bone strength

  • birth defects

  • Increased risk for lung cancer in smokers

*UL = 3,000μg RAE/day

• Carotenoids

  • NOT toxic

  • supplements are not recommended

  • only thing that can happen is

    Carotenemia (Orange skin)

Vitamin D 

• “Sunshine vitamin”- With UV light exposure, can be produced from cholesterol in the skin

• Limited sun exposure → essential to consume Vitamin D in the diet

• Must be activated in the liver and kidneys to fulfil its biological function!

Vitamin D Functions

• Acts as a hormone

• helps bone growth/maintenance

• regulates calcium metabolism

  • Blood levels, absorption, excretion

• regulates protein synthesis

• possibly regulates cardiovascular function?

Dietary sources of Vitamin D

• fatty fish, cheese, eggs, and a few others are the few with vit D naturally

• fortified foods (such as milk) are good sources

• Vitamin D2 = Ergocalciferol (from plant sources)

• Vitamin D3 = Cholecalciferol (from animal sources) (ALSO the form our body makes)

RDA = 15 mcg/day (at the age of 70 it INC to 20 to help with bone loss)

Sunlight exposure

Interferes with one’s ability to make Vitamin D:

• Living far away from the equator

• Wearing sunscreen

• Staying indoors

• Having darker skin (they need 3x more)

• aging

Vitamin D Activation

1. synthesis by the skin or consumed by the diet

2. enters circulation and is transported to the liver

3. conversion to active begins in the liver, anf is finished in the kidneys

Vitamin D and Blood Calcium Maintenance

• most calcium is stored in the bones; less than 1% circulates the blood. It is very important!

• 1. Parathyroid glands- the parathyroid hormone is released from here in response to low blood calcium levels

• 2. Kidney – Calcitriol increases calcium reabsorption in the kidneys

  (So less calcium is lost in urine.)

• 3. Bone- calcitriol increases calcium release from bone

• 4. Intestine – Calcitriol increases the absorption of calcium from the intestine

**Calcitriol is what Vit D is converted to!

Vitamin D Deficiency 

• Rickets- bowed legs and knocked knees (in children)

• Osteopenia- soft/weakened bones! painful (in adults) 

• Other chronic diseases:

  • cancer

  • Autoimmune disease

  • Kidney disease

  • Type 2 diabetes

  • Cardiovascular disease

Vitamin D toxicity

• Hypervitaminosis D

  • from too may supplements 

  • Excessive calcitriol (active Vitamin D)

  • Leads to hypercalcemia (too much calcium in the blood)

  • Symptoms may include:

    • Loss of appetite

    • Weight loss

    • Irregular heartbeat

    • Frequent urination

    • Leads to the calcification of soft tissues and damage to the heart and blood vessels, as well as the formation of kidney stones

**UL = 100 mcg/day (4,000 IUD)

Vitamin E

• encompass a group of fat soluble compounds called tocopherols 

  • Most active form = α-tocopherol

• functions as an antioxidant!

  • incorporated into cell membranes

  • in LDL’s (that would otherwise increase plaque forming potential)

  • In white blood cells that mainine immune function

DIetary sources of Vitamin E

• Best sources- Nuts/seeds/some oils/dark leafy greens

• easily destroyed in food prep/storage (so low/no heat and airtight containers help

Vitamin E and protects cell membranes

• since it’s fat soluble vitamin E is great at stopping oxidation in membranes and LDL’s

• role in reducing plaque formation in blood vessels and protects white blood cells from oxidation

• other antioxidants help make each other more active and effective! (like Vit C)

Vitamin E protects from chronic disease

• cancer-

  • Antioxidant nutrients protect DNA

  • Diets ↑ Vitamin E associated with ↓ cancer risk

• cardiovascular disease-

  • May ↓ plaque formation

  • Supplementation NOT encouraged 

• cataracts-

  • Related to free radical damage

  • Antioxidants may delay or prevent 

Vitamin E Deficiency and Toxicity

Deficiencies

• RARE!

• Neuromuscular problems

• Hemolytic anemia

*infant formula now fortified with vitamin E

Toxicity-

• Less likely to be toxic tha Vit A or D

• UL = 1000 mcg/day (1500 UL) which is 60x the RDA

• only observed with high supplement intake! 

• INC the tendency to bleed, which can have real bad effects

  • such as hemorrhagic stroke! 

Vitamin K

• Functions:

  • needed for protien synthesis

  • needed for blood clotting

    • deficiencies can cause uncontrolled bleeding! since the blood clotting is what typically stops the bleeding

  • bone metabolism

    • modifies bone proteins- which allows them to bind calcsum and regulate bone function

The Three Forms of Vitamin K

1. Vitamin K1 – plant (aka the food we eat)

2. Vitamin K2 - bacteria

3. Vitamin K3 - synthetic (Commercially produced)

Dietary Sources of Vitamin K

• Best source- leafy greens!

• some cheese, fruit, veggies, and veg oils are also pretty good

Vitamin K and blood clotting

1. Vitamin K + calcium activate clotting factors

2. Activated clotting factors convert prothrombin → thrombin

3. Thrombin converts fibrinogen → fibrin

4. Fibrin forms the blood clot

Vitamin K Deficiency and Toxicity

• Deficiency

  • Rare

  • potential causes:

    • Fat malabsorption

    • medications

  • Consequences

    • hemorrhaging (excessive or uncontrolled bleeding)

    • fractures

• Toxicity

  • No evidence of toxicity at any level, so there is no UL 

Vitamin K is given at birth

• since the early 1960’s at birth infants have been given vit K

  • Reduces hemorrhage risk because they have limited liver stores (vit K is stored in the liver) and vitamin K is low in breast milk 

  • Intestinal bacteria not yet producing vitamin K