Describe the general characteristics of fat- and water-soluble vitamins, including absorption and storage.
List methods for preserving vitamins in foods and explain sources and benefits of phytochemicals.
Describe the main functions of each vitamin.
Identify the best dietary sources for each vitamin and dangers of exceeding recommended intakes.
Discuss signs and symptoms of vitamin deficiencies and risk factors leading to them.
Evaluate dietary supplements, including current recommendations and potential benefits and hazards of use.
Vitamins Contribute to Many Functions
Vitamins are essential for various bodily functions including:
Fluid and Electrolyte Balance: Involves vitamins such as Thiamin, Riboflavin, Niacin, Pantothenic acid, Biotin, Vitamin B-12, and minerals like Iodine, Chromium, Magnesium, Manganese, Molybdenum, Choline, Sodium, Potassium, Chloride, and Phosphorus.
Body Defenses: Includes vitamins A, C, D, E, and Carotenoids.
Bone Health: Involves Vitamin C, D, K, Calcium, Phosphorus, Magnesium, Fluoride, and Boron.
Brain Health: Includes Thiamin, Riboflavin, Niacin, Vitamin B-6, B-12, Folate, Choline, Vitamin C, Selenium, and Copper.
Blood Health: Comprises Iron, Magnesium, Manganese, Vitamins D, E, and K, Calcium, Zinc, and Copper.
Definition and Characteristics of Vitamins
Vitamins: Carbon-containing compounds required in small amounts by the body.
Essential Vitamins: Cannot be synthesized in sufficient quantities by the body, and absence can lead to deficiency that may be reversed by resupplying the vitamin.
Toxicity: Avoid excessive intakes over the upper limits (megadoses).
Vitamin Toxicity
Fat-soluble Vitamins: A, D, E are not easily excreted from the body, potentially leading to toxicity, with Vitamin A toxicity being the most reported.
Water-soluble Vitamins: Generally excreted in urine; exceptions are Vitamins B-6 and B-12, which can be stored in the liver.
Most vitamin toxicity occurs from supplement sources, not from foods.
Vitamin Preservation in Foods
Vitamin content is maximal when fruits and vegetables are ripe.
Freezing: Helps retain vitamins.
Water-soluble vitamins are particularly sensitive to:
Heat
Light
Air exposure
Cooking in water
Alkalinity
MyPlate Sources of Vitamins
Grains: Folic acid, Niacin, Riboflavin, Thiamin.
Dairy: Choline, Riboflavin, Vitamin B-12, Vitamin D.
Fruits: Folate, Vitamin A, Vitamin C.
Vegetables: Folate, Vitamin A, Vitamin C, Vitamin K.
Forms of Vitamin A: Known as retinoids, encompassing three active forms: Retinol, Retinal, and Retinoic acid, all derived from animal products and supplements typically contain retinyl acetate or retinyl palmitate.
Functions of Vitamin A
Vision: Prevents night blindness and macular degeneration, both significant health concerns related to aging and deficiency.
Growth, Development, and Reproduction: Essential for protein synthesis necessary for growth and reproduction processes, as well as differentiating and maturing cells into tissues and organs.
Consequences of Deficiency: Can lead to stunted growth in children and impair reproductive health.
Getting Enough Vitamin A
RDA and DV for Vitamin A:
Adult males: 900 mcg RAE (Retinol Activity Equivalents) per day.
Adult females: 700 mcg RAE per day.
Best sources include liver, fish, fortified milk, butter, yogurt, eggs, and certain vegetables.
Reserves stored mainly in the liver.
Food Sources of Carotenoids
Rich in dark-green and yellow-orange fruits and vegetables, with specific sources including:
Beta-carotene: Green leafy vegetables like spinach and kale.
Lutein and Zeaxanthin: Found in various fruits and vegetables, including tomatoes (lycopene).
Vitamin A Toxicity
Upper Limit (UL): 3000 mcg RAE; risks include liver toxicity, increased fracture risk, poor pregnancy outcomes, and birth defects.
Overconsumption of carotenoids, like from carrots, can induce hypercarotenemia, resulting in yellow-orange skin discoloration but is reversible.
Vitamin D
Synthesis of Vitamin D
Sources: The precursor for Vitamin D is 7-dehydrocholesterol, located in the skin, which is converted to D3 upon exposure to sunlight.
Two forms:
Vitamin D2 (ergocalciferol) - synthetic.
Vitamin D3 (cholecalciferol) - naturally derived.
Both forms travel to the liver, where they are converted into calcidiol (25-hydroxyvitamin D3), then to the active calcitriol (1,25-dihydroxyvitamin D3) in the kidneys.
Functions of Vitamin D
Regulates calcium and phosphorus levels in the blood, aiding in:
Gene expression
Cell growth regulation
Neuromuscular and immune functions
Inflammation reduction
Potential cancer risk reduction
Works synergistically with parathyroid hormone (PTH) to control calcium excretion and deposition in bones.
Getting Enough Vitamin D
Recommended Dietary Allowance (RDA):
15 mcg for individuals aged 1-70 years.
20 mcg for individuals aged 71 years and older.
Typically obtained from limited dietary sources such as fatty fish, fortified dairy products, and mushrooms.
Thiamin (Vitamin B-1)
Functions of Thiamin
Essential for releasing energy from carbohydrates and is a coenzyme in ATP-producing pathways (thiamin pyrophosphate or TPP).
Participates in DNA, RNA, and neurotransmitter synthesis.
Folate
Functions of Folate
Vital for cell division and acts as a coenzyme that supplies single carbon compounds.
Aids in the formation of DNA and metabolizing amino acids.
Folic acid is the synthetic form and is commonly added to fortified foods.
Folate Deficiency
Can lead to megaloblastic anemia, characterized by large, immature red blood cells that fail to divide correctly. This condition can arise from deficiencies in either folate or vitamin B-12.
Maternal folate deficiency increases risk for neural tube defects in the developing fetus, emphasizing the recommendation for women to take folic acid supplements before and during pregnancy.
Vitamin B-12
Functions and Deficiency of Vitamin B-12
Found only in animal-derived foods, Vitamin B-12 deficiency is prevalent in vegans and may manifest as:
Neurological symptoms due to destruction of the myelin sheath.
Pernicious anemia due to inadequate absorption rather than dietary deficiency.
The daily nutritional requirements can be met via animal products or fortified foods.
Vitamin C
Getting Enough Vitamin C
Adult RDA:
Women: 75 mg per day
Men: 90 mg per day
Tobacco users require an additional 35 mg due to increased oxidative stress.
Average U.S. consumption is between 70 to 100 mg/day.
Excess Vitamin C
The Upper Limit for Vitamin C is set at 2000 mg per day; excessive intake may lead to iron absorption issues, gastrointestinal distress, and diarrhea.
Dietary Supplements
Dietary Supplement Health and Education Act (DSHEA) of 1994
Defines dietary supplements as products intended to supplement the diet containing:
Vitamins, minerals, herbs, amino acids, or other dietary substances.
The supplement industry generates approximately $35 billion annually in the U.S.
Should You Take a Supplement?
Generally recommended only as a back-up plan to fill dietary gaps, with an emphasis on food sources for nutrients.
Current evidence does not strongly endorse the regular use of multivitamins for chronic disease prevention.
Choosing a Supplement
Opt for a nationally recognized brand.
Ensure it contains Daily Values for nutrients.
Take with meals for better absorption and check for the USP symbol that indicates product quality.
Cancer-Fighting Foods
Foods of plant origin are pivotal in cancer prevention due to their nutrient-rich profiles, containing phytochemicals such as antioxidants that may prevent DNA mutations.
Vitamins C and E specifically help prevent the formation of carcinogenic compounds in the gastrointestinal tract.
Following MyPlate guidelines can assist in forming a cancer-fighting diet.