Vitamins for adults

Vitamins are substances that help regulate important body cell functions. Vitamins help change food into energy, and they're also needed for the formation of red blood cells, good vision, strong bones and teeth, and to ensure proper heart and nervous system function. Since your body doesn't produce most vitamins, you need to get them from food.


General information
There are two kinds of vitamins: water-soluble and fat-soluble. Water-soluble vitamins dissolve in water and are carried in the bloodstream throughout the body. Vitamin C and the B complex vitamins are all water-soluble. Since these vitamins dissolve in water, they're not stored well in the body. Because water is lost through your breath, urine and sweat, you must replace water-soluble vitamins daily. However, megadoses of even water-soluble vitamins can be harmful. For example, repeatedly taking supplements of vitamin B6 that greatly exceed the recommended daily allowance can cause nerve damage.
The fat-soluble vitamins -- A, D, E and K -- dissolve in fats. They are carried through the body attached to substances that are attached to fats in the bloodstream. Since the body stores fat better than water, you don't have to replace these vitamins as often. In fact, if you take large doses of these vitamins over a long period of time, you can store up so much that it harms your health. For example, high levels of vitamins A and D can become toxic.

Vitamins A (beta carotene), C and E are antioxidants. They help protect the body from the damaging effects of free radicals.

Fruits and vegetables are good sources of vitamins. If they're improperly handled or cooked, however, the vitamins can be easily destroyed. To avoid this, it's best to refrigerate fresh fruits and vegetables and use them within three to four days of purchase. To cook vegetables with minimum vitamin loss, steam them in a small amount of water or use a microwave. When fresh produce isn't available, frozen or canned varieties can also be a good source of vitamins.


Nutrition terminology
Trying to make sense of your nutrition requirements can be confusing and sometimes even overwhelming. Here are definitions of some of the most common nutrition terms you may encounter:
Recommended dietary allowance (RDA) is the recommended daily amount of a nutrient most people need to stay healthy. These recommendations were developed by the Food and Nutrition Board of the National Academy of Sciences. They were last revised in 1989.

Adequate intake (AI) is the recommended daily amount of a nutrient needed when an RDA cannot be determined.

Tolerable upper intake level (UL) is the maximum daily amount of a nutrient that is not likely to have harmful health effects for people in the general population.

Dietary reference intake (DRI) is the term used for a set of nutrient reference values. These values include the RDA, AI and UL nutrient recommendations. Many nutrient requirements have been updated since the RDAs were originally set. The DRIs were developed in 2000 based on current nutrition research.

Many conditions can affect your daily nutritional requirements, including your age, health status, weight and sex. Elderly adults and women who are pregnant or nursing may have enhanced nutritional needs. Your lifestyle habits, such as smoking or drinking excessive amounts of alcohol, can also have an impact on your nutritional needs. Consult your doctor about health factors that may affect your nutritional needs. Discuss your child's nutritional needs with his or her doctor.


Water-soluble vitamins
Vitamin C
Vitamin C (ascorbic acid) promotes healthy gums, teeth, connective tissue and bones. It also helps maintain your immune system and aids wound healing. A prolonged vitamin C deficiency can cause scurvy (a condition characterized by joint pain, bleeding gums and weakness), delayed wound healing and poor immune system response. On the other end of the spectrum, long-term excessive consumption of vitamin C may lead to side effects such as facial flushing, stomach cramps, diarrhea, nausea, vomiting, kidney stones and headaches.

Fruits and vegetables are often good sources of vitamin C, including:

citrus fruits and juices
strawberries, kiwi, guava and papaya
broccoli, cabbage, red peppers and brussels sprouts
tomatoes
potatoes
DRIs for vitamin C are:

90 milligrams for men
75 milligrams for women
Smokers need to add an additional 35 milligrams per day to their total intake of vitamin C because smoking depletes this important vitamin.

Vitamin B1
Vitamin B1 (thiamine) helps convert carbohydrates into energy. It's vital for normal growth and development, the health of mucus membranes and proper muscle performance. Vitamin B1 also helps maintain a healthy nervous system and heart. A prolonged vitamin B1 deficiency can result in fatigue, weak muscles, nerve damage or beriberi (a condition that causes nerve and heart failure). Alcohol impairs thiamine absorption, so alcoholics are often thiamine-deficient.

Good sources of vitamin B1 include:

whole grains, nuts and dried sunflower seeds
navy beans, kidney beans and soybeans
pork, red meat and organ meats
brewer's yeast, wheat germ and rice bran
RDAs for vitamin B1 are:

1.2 milligrams per day for men
1.1 milligrams per day for women
Vitamin B2
Vitamin B2 (riboflavin) helps protect the nervous system, mucus membranes, skin and eyes. A vitamin B2 deficiency can cause cataracts (a cloudy area in the lens of the eye, the clear structure that focuses light rays onto the retina), dry skin and a sore tongue. Side effects of taking large doses of riboflavin are unknown.

Good sources of vitamin B2 include:

milk, cheese and yogurt
chicken and beef liver
leafy green vegetables
cereal
bread
wheat germ
almonds
RDAs for vitamin B2 are:

1.3 milligrams per day for men
1.1 milligrams per day for women
Vitamin B3
Vitamin B3 (niacin) helps convert food into energy and make genetic DNA (a substance found in the center of cells that carries hereditary information). It helps keep the skin, nerves and digestive system healthy. A niacin deficiency can cause pellagra (a condition which can cause diarrhea, mental disorders and skin problems). Too much niacin can cause flushing of the skin, rashes, liver damage, nausea, vomiting or abdominal pain.

Good sources of vitamin B3 include:

poultry
pork
beef
veal
salmon, swordfish, halibut, and other types of fish and tuna
peanuts and sunflower seeds
fortified cereal
RDAs for vitamin B3 are:

16 milligrams NE (niacin equivalents) per day for men
14 milligrams NE (niacin equivalents) per day for women
Vitamin B6
Vitamin B6 (pyridoxine) helps your body use dietary protein, fats and carbohydrates. Vitamin B6 helps maintain brain function, form red blood cells, and keep your immune system working. A prolonged lack of vitamin B6 can cause convulsions, anemia (a condition marked by a decreased number of red blood cells or hemoglobin, a protein in red blood cells that contains iron), nausea or flaky skin. For infants, a lack of vitamin B6 can cause seizures. Too much of this vitamin can produce nerve damage and depression.

Good sources of vitamin B6 include:

meat
salmon, other types of fish, shrimp and tuna
bananas, avocados and watermelon
lentils, sunflower seeds and whole grains
peanut butter
almonds
RDAs for vitamin B6 are:

1.3 milligrams per day for adults
Vitamin B12
Vitamin B12 (cyanocobalamin) helps the body form red blood cells, use fats and carbohydrates, and maintain normal nervous system function. A prolonged vitamin B12 deficiency can result in anemia, fatigue or nerve damage.

Good sources of vitamin B12 are animal products, including:

clams, flounder, herring, mackerel, sardines, salmon and snapper
dairy foods, including milk, blue cheese, Swiss cheese, cottage cheese, yogurt and mozzarella cheese
beef, chicken and pork
eggs
fortified skim milk
Since vitamin B12 is not found in any plant foods, strict vegetarians should consume B12-fortified cereals and soy milk to prevent a vitamin B12 deficiency.

RDAs for vitamin B12 are:

2.4 micrograms per day for adults
Folic acid
Folic acid (folate) helps form red blood cells and genetic DNA. A folic acid deficiency can cause anemia and lead to weight loss, gastrointestinal problems and a burning sensation in the tongue. Too much folic acid can cause crystals to form in the urine, appetite loss, nausea, gas or possible nerve damage. Very early in pregnancy, folic acid helps develop the neural tube of the fetus. Without adequate amounts of this important vitamin, serious brain and spinal cord birth defects can occur. Therefore, it's important for all women who may become pregnant to get enough folic acid.

Good sources of folic acid include:

broccoli, spinach and romaine lettuce
oranges and orange juice
wheat germ
beans, peas and lentils
whole grains
fortified cereals and grain products
RDAs for folic acid are:

400 micrograms per day for adults
600 micrograms per day during pregnancy
Biotin
Biotin, to some extent, is made by the "good" bacteria in your intestines. Biotin helps your body use protein, fats and carbohydrates. It helps nerve tissue, blood cells, bone marrow, skin and hair to grow. It also helps male sex glands to function. No harmful side effects have been identified with excess biotin. However, an inadequate amount can result in scaly skin, appetite loss, fatigue or depression.

Good sources of biotin include:

nuts and sunflower seeds
vegetables
fish
egg yolk
whole grains
brewer's yeast
dairy products
meat, especially liver
Thirty micrograms per day for adults is considered an adequate intake of biotin.

Pantothenic acid
Pantothenic acid helps the body make energy and use protein, fats and carbohydrates. Deficiencies of this vitamin are rare, but include fatigue and gastrointestinal symptoms. Side effects of large amounts are unknown.

Good sources of pantothenic acid include:

broccoli
poultry
fish
whole grains
avocado
milk
vegetables
mushrooms
Five milligrams per day for adults is considered an adequate intake of pantothenic acid.


Fat-soluble vitamins
Vitamin A
Vitamin A (retinol) promotes good vision, especially at night. It also helps form and maintain skin, teeth, bones, hair and mucus membranes. Your body breaks down beta carotene into vitamin A, so you can eat foods high in either vitamin A or beta carotene to meet your recommended vitamin A needs. Prolonged vitamin A deficiency may cause infertility, dry skin, stunted growth and night blindness. Too much over a long period of time can cause hair loss, headaches, bone thickening, liver enlargement, menstrual problems, joint pain, weakness and dry skin. It may also lead to an increased risk of fractures.

Good sources of vitamin A and beta carotene include:

dark-green, leafy vegetables (such as broccoli, spinach and kale)
yellow and orange vegetables and fruits (such as carrots, sweet potatoes, winter squash, apricots, cantaloupe and mangoes)
eggs
beef or chicken liver
DRIs for vitamin A are:

900 micrograms (or retinol equivalents, the standard measurement for vitamin A activity in foods) per day for men or 4,500 IU (international units, often listed on food or supplement labels
700 micrograms (retinol equivalents) per day for women or 3,500 IU
Vitamin D
Vitamin D promotes strong bones, teeth and cartilage by helping your body absorb calcium and phosphorus. Your body manufactures vitamin D when you're exposed to sunlight, and it's in a small selection of food products. Insufficient vitamin D can cause rickets (a disease that produces brittle bones and teeth). In high doses, especially over long periods of time, vitamin D can hurt the kidneys, heart and interfere with normal growth in children.

In addition to sun exposure, good sources of vitamin D include:

sun exposure
fortified milk
fortified cereals
beef and veal
herring, mackerel, salmon and sardines
egg yolks
Adequate intake for vitamin D is considered:

5 micrograms per day for people ages 19 to 50 or 200 IU (international units, often listed on food or supplement labels)
10 micrograms per day for people ages 51 to 70 or 400 IU
15 micrograms per day for people older than age 70 or 600 IU
Vitamin E
Vitamin E (alpha-tocopherol) helps prevent cell breakdown and blood clots. It also helps your body produce red blood cells. Because of the amount of vitamin E present in foods, vitamin E deficiencies do not take place in the general population. Although it's a fat-soluble vitamin, it takes a lot of vitamin E to cause health problems. At very high doses, vitamin E may increase the effects of blood-thinning medications.

Good sources of vitamin E include:

vegetable oils
nuts and seeds
wheat germ and whole-wheat flour
margarine
spinach, lettuce and broccoli
sweet potato
shrimp
DRIs for vitamin E (alpha-tocopherol) are:

15 milligrams for adults or 22 IU (international units, often listed on food or supplement labels)
Vitamin K
Vitamin K helps blood clot -- if you don't have enough, serious clotting disorders occur. Very large doses seem tolerated by the body, but in rare cases too much can cause liver or brain damage for infants. Vitamin K is made by the "good" bacteria in your intestines.

Good sources of vitamin K include:

dark green leafy vegetables, including brussels sprouts and spinach
cabbage, broccoli and cauliflower
oats and soybeans
dairy products
egg yolks
Adequate intake (AIs) for vitamin K are:

120 micrograms per day for men
90 micrograms per day for women

Vitamin supplements
Most people who eat a well-balanced diet generally don't need a daily multivitamin supplement. Many researchers are now recommending a basic daily vitamin and mineral supplement, however. If you're considering taking a supplement, you may want to ask your doctor if it's necessary. If you choose to take a multivitamin supplement, select one that contains 100 percent of the RDA for a variety of vitamins and minerals.
Vitamin supplements are often recommended to meet the special needs of pregnant women. Folic acid supplements are recommended for all women in their childbearing years to prevent neural-tube birth defects. Others who may benefit from a vitamin supplement include:

elderly adults (especially if you're reducing food intake for any reason)
heavy drinkers
teenagers with poor dietary habits
smokers
chronic dieters
people with impaired immune systems
people who take certain long-term medication therapy
children
strict vegetarians