Fat-Soluble Vitamins
by J. Anderson and L. Young1
Quick Facts...
a.. Small amounts of vitamins A, D, E and K are needed to maintain good
health.
b.. Foods that contain these vitamins will not lose them when cooked.
c.. The body does not need these every day and stores them in the liver
when not used.
d.. Most people do not need vitamin supplements.
e.. Megadoses of vitamins A, D, E or K can be toxic and lead to health
problems.
Vitamins are essential nutrients your body needs in small amounts for
various roles in the human body. Vitamins are divided into two groups:
water-soluble (B-complex and C) and fat-soluble (A, D, E and K). Unlike
water-soluble vitamins that need regular replacement in the body, fat-soluble
vitamins are stored in the liver and fatty tissues, and are eliminated much more
slowly than water-soluble vitamins.
Because fat-soluble vitamins are stored for long periods, they generally
pose a greater risk for toxicity than water-soluble vitamins when consumed in
excess. Eating a normal, well-balanced diet will not lead to toxicity in
otherwise healthy individuals. However, taking vitamin supplements that contain
mega doses of vitamins A, D, E and K may lead to toxicity. Remember, the body
only needs small amounts of any vitamin.
While diseases caused by a lack of fat-soluble vitamins are rare in the
United States, symptoms of mild deficiency can develop without adequate amounts
of vitamins in the diet. Additionally, some health problems may decrease the
absorption of fat, and in turn, decrease the absorption of vitamins A, D, E and
K. Consult your doctor about this.
Table 1 lists sources of fat-soluble vitamins, their basic functions in
the body, major deficiency symptoms caused by a lack of these vitamins, and
symptoms of over-consumption.
Vitamin A
Vitamin A, also called retinol, has many functions in the body. In
addition to helping the eyes adjust to light changes, vitamin A plays an
important role in bone growth, tooth development, reproduction, cell division
and gene expression. Also, the skin, eyes and mucous membranes of the mouth,
nose, throat and lungs depend on vitamin A to remain moist.
The best way to ensure your body gets enough vitamin A is to eat a variety
of foods. Vitamin A is supplied primarily by certain foods of animal origin like
dairy products, fish and liver. Some foods of plant origin contain
beta-carotene, an antioxidant that the body converts to vitamin A.
Beta-carotene, or provitamin A, comes from fruits and vegetables. Carrots,
pumpkin, winter squash, dark green leafy vegetables and apricots are rich
sources of beta-carotene.
The recommendation for vitamin A intake is expressed as micrograms (mcg)
of retinol activity equivalents (RAE). Retinol activity equivalents account for
the fact that the body converts only a portion of beta-carotene to retinol. One
RAE equals 1 mcg of retinol or 12 mcg of beta-carotene (see Table 2).
True vitamin A deficiency in the United States is rare. Night blindness
and very dry, rough skin may indicate a lack of vitamin A. Other signs of
possible vitamin A deficiency include decreased resistance to infections, faulty
tooth development, and slower bone growth.
In the United States, toxic or excess levels of vitamin A are of more
concern than deficiencies. The tolerable upper intake level for adults is 3,000
mcg RAE. It would be difficult to reach this level consuming food alone. But
some multivitamin supplements contain high doses of vitamin A. If you take a
multivitamin, check the label to be sure the majority of vitamin A provided is
in the form of beta-carotene, which appears to be safe. Symptoms of vitamin A
toxicity include dry, itchy skin, headache, nausea, and loss of appetite. Signs
of severe overuse over a short period of time include dizziness, blurred vision
and slowed growth. Vitamin A toxicity also can cause severe birth defects and
may increase the risk for hip fractures.
Physicians sometimes recommend that young infants take vitamin supplements
that contain vitamin A. However, toddlers and children need protection from too
much vitamin A due to their smaller body size. Typical foods eaten in large
amounts by toddlers and children usually contain sufficient amounts of vitamin
A. Provide a variety of foods for your children, and if in doubt, check with a
pediatrician or Registered Dietitian.
Table 1: Vitamin facts.
Vitamin Source Physiological Functions Deficiency Overconsumption
A (retinol) (provitamin A, such as beta carotene) Vitamin A: liver,
vitamin A fortified milk and dairy products, butter, whole milk, cheese, egg
yolk.
Provitamin A: carrots, leafy green vegetables, sweet potatoes,
pumpkins, winter squash, apricots, cantaloupe. Helps to form skin and mucous
membranes and keep them healthy, thus increasing resistance to infections;
essential for night vision; promotes bones and tooth development. Beta carotene
is an antioxidant and may protect against cancer. Mild: night blindness,
diarrhea, intestinal infections, impaired vision.
Severe: inflammation of eyes, keratinization of skin and eyes.
Blindness in children. Mild: nausea, irritability, blurred vision.
Severe: growth retardation, enlargement of liver and spleen, loss of
hair, bone pain, increased pressure in skull, skin changes.
D Vitamin D-fortified dairy products, fortified margarine, fish
oils, egg yolk. Synthesized by sunlight action on skin. Promotes hardening of
bones and teeth, increases the absorption of calcium. Severe: rickets in
children; osteomalacia in adults. Mild: nausea, weight loss, irritability.
Severe: mental and physical growth retardation, kidney damage,
movement of calcium from bones into soft tissues.
E Vegetable oil, margarine, butter, shortening, green and leafy
vegetables, wheat germ, whole grain products, nuts, egg yolk, liver. Protects
vitamins A and C and fatty acids; prevents damage to cell membranes.
Antioxidant. Almost impossible to produce without starvation; possible anemia in
low birth-weight infants. Nontoxic under normal conditions.
Severe: nausea, digestive tract disorders.
K Dark green leafy vegetables, liver; also made by bacteria in the
intestine. Helps blood to clot. Excessive bleeding. None reported.
Vitamin D
Vitamin D plays a critical role in the body's use of calcium and
phosphorous. It increases the amount of calcium absorbed from the small
intestine and helps form and maintain bones. Children especially need adequate
amounts of vitamin D to develop strong bones and healthy teeth.
The primary food sources of vitamin D are milk and other dairy products
fortified with vitamin D. Vitamin D is also found in oily fish (e.g., herring,
salmon and sardines) as well as in cod liver oil. In addition to the vitamin D
provided by food, we obtain vitamin D through our skin which makes vitamin D in
response to sunlight.
An Adequate Intake (AI) for has been established for vitamin D (see Table
2). The AIs for vitamin D appear as micrograms (mcg) of cholecalciferol. Ten mcg
of cholecalciferol equals 400 International Units (IU).
Symptoms of vitamin D deficiency in growing children include rickets
(long, soft bowed legs) and flattening of the back of the skull. Vitamin D
deficiency in adults is called osteomalacia, which results in muscular weakness
and weak bones. These conditions are rare in the United States.
The tolerable upper intake level for vitamin D is set at 50 mcg for people
1 year of age and older (see Table 3). High doses of vitamin D supplements
coupled with large amounts of fortified foods may cause accumulations in the
liver and produce signs of poisoning. Signs of vitamin D toxicity include excess
calcium in the blood, slowed mental and physical growth, decreased appetite,
nausea and vomiting.
It is important that infants and young children do not consume excess
amounts of vitamin D regularly. Children exposed to the sun for 5 to 10 minutes
daily will produce enough vitamin D. However, if children live in inner cities,
wear clothes that cover most of their skin or live in northern climates where
little sun is seen in the winter, then vitamin D deficiency may occur. Rather
than give children a supplement, add fortified foods to their diet, such as
vitamin D fortified milk and other dairy products.
Table 2: Dietary Reference Intakes (DRI) for fat soluble vitamins.
Life Stage Group Vitamin A (mcg1) Vitamin A (IU) Vitamin D (mcg2)
Vitamin D (IU) Vitamin E (mg a-TE3) Vitamin E (IU)
Infants 0.0-0.5 400* 1333 5* 200 4* 6
0.5-1.0 500* 1666 5* 200 5* 7.5
Children 1-3 300 1000 5* 200 6 9
4-8 400 1333 5* 200 7 10.5
Males 9-13 600 2000 5* 200 11 16.5
14-18 900 3000 5* 200 15 22.5
19-30 900 3000 5* 200 15 22.5
31-50 900 3000 5* 200 15 22.5
51-70 900 3000 10* 400 15 22.5
71+ 900 3000 15* 600 15 22.5
Females 9-13 600 2000 5* 200 11 16.5
14-18 700 2333 5* 200 15 22.5
19-30 700 2333 5* 200 15 22.5
31-50 700 2333 5* 200 15 22.5
51-70 700 2333 10* 400 15 22.5
71+ 700 2333 15* 600 15 22.5
Pregnant <18 750 2500 5* 200 15 22.5
19-30 770 2566 5* 200 15 22.5
31-50 770 5* 200 15 22.5
Lactating <18 1,300 4000 5* 200 19 28.8
19-30 1,300 4333 5* 200 19 28.8
31-50 1,300 4333 5* 200 19 28.8
*Indicates an Adequate Intake (AI). All other values are Recommended
Dietary Allowance (RDA).
1As retinol activity equivalents (RAEs). 1 RAE = 1mcg retinol or 12
mcg beta-carotene.
2 As cholecalciferol. 10 mcg cholecalciferol = 400 IU of vitamin D.
3 As alpha-tocopherol equivalents. 1 mg of alpha-tocopherol = 1.5 IU
of vitamin E.
Vitamin E
Vitamin E acts as an antioxidant, protecting vitamins A and C, red blood
cells and essential fatty acids from destruction. Research from a decade ago
suggested that taking antioxidant supplements, vitamin E in particular, might
help prevent heart disease and cancer. However, newer findings indicate that
people who take antioxidant supplements are not better protected against heart
disease and cancer than non-supplement users. On the other hand, there are many
studies that show a link between regularly eating antioxidant-rich fruits and
vegetables and a lower risk for heart disease, cancer and several other
diseases.
The RDA for vitamin E is based on the most active and usable form called
alpha-tocopherol (see Table 2). One milligram of alpha-tocopherol equals to 1.5
International Units (IU).About 60 percent of vitamin E in the diet comes from
vegetable oil or products made with vegetable oils. Therefore, good food sources
of vitamin E include vegetable oils and margarines. Vitamin E is also found in
fruits and vegetables, grains, nuts, seeds and fortified cereals.
Vitamin E deficiency is rare. Cases of vitamin E deficiency only occur in
premature infants and people unable to absorb fats.
The tolerable upper intake levels for vitamin E are shown in Table 3.
Large doses of vitamin E pose a hazard to people who take blood-thinning
medications. People taking statin drugs are also not advised to take
supplemental vitamin E because it may interfere with how the medication works.
Vitamin K
Naturally produced by the bacteria in the intestines, vitamin K plays an
essential role in normal blood clotting and helps promote bone health.
Good food sources of vitamin K are green vegetables such as turnip greens,
spinach, cauliflower, cabbage and broccoli, and certain vegetables oils
including soybean oil, cottonseed oil, canola oil and olive oil. Animal foods,
in general, contain limited amounts of vitamin K.
To help ensure people receive sufficient amounts of vitamin K, an Adequate
Intake (AI) has been established for each age group (see Table 2).
Without sufficient amounts of vitamin K, hemorrhaging can occur.
Deficiencies may appear in infants, or in people who take anticoagulants or
antibiotic drugs. Newborn babies lack the intestinal bacteria to produce vitamin
K and need a supplement for the first week. People on anticoagulant drugs (blood
thinners) may become deficient in vitamin K, but should not change their vitamin
K intake without consulting a physician because the effectiveness of the drug
may be affected. People taking antibiotics may lack vitamin K temporarily
because intestinal bacteria are sometimes killed as a result of long-term use of
antibiotics. Also, people with chronic diarrhea may have problems absorbing
sufficient amounts of vitamin K through the intestine and should consult their
physician to determine if supplementation is necessary.
Although a tolerable upper intake level has not been established for
vitamin K, excessive amounts can cause the breakdown of red blood cells and
liver damage. Large doses are not advised.
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