The fat-soluble vitamins, A, D, E, and K, are stored in the body for long periods
of time and generally pose a greater risk for toxicity when consumed in excess
than water-soluble vitamins. Eating a normal, well-balanced diet will not lead
to toxicity in otherwise healthy individuals. However, taking vitamin supplements
that contain megadoses of vitamins A, D, E and K may lead to toxicity. The body
only needs small amounts of any vitamin.
While diseases caused by a lack of fat soluble vitamins are rare 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 a medical
professional about any potential health problems that may interfere with vitamin
absorption.
RETINOL
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, gene expression,
and regulation of the immune system. The skin, eyes, and mucous membranes
of the mouth, nose, throat and lungs depend on vitamin A to remain moist.
Vitamin A is also an important antioxidant that may play a role in the prevention
of certain cancers.
Food Sources for Vitamin A
Eating a wide variety of foods is the best way to ensure that the body gets enough
vitamin A. The retinol, retinal, and retinoic acid forms of vitamin A are supplied
primarily by foods of animal origin such as dairy products, fish and liver. Some
foods of plant origin contain the antioxidant, betacarotene, which the body
converts to vitamin A. Beta-carotene, comes from fruits and vegetables,
especially those that are orange or dark green in color. Vitamin A sources also
include carrots, pumpkin, winter squash, dark green leafy vegetables and
apricots, all of which are rich in beta-carotene.
How much Vitamin A
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 betacarotene to retinol. One RAE
equals 1 mcg of retinol or 12 mcg of beta-carotene. The Recommended Dietary
Allowance (RDA) for vitamin A is 900 mcg/ day for adult males and 700 mcg/
day for adult females.
Compared to vitamin A, it takes twice the amount of carotene rich foods to meet
the body’s vitamin A requirements, so one may need to increase consumption
of carotene containing plant foods. Recent studies indicate that vitamin A
requirements may be increased due to hyperthyroidism, fever, infection, cold,
and exposure to excessive amounts of sunlight. Those that consume excess
alcohol or have renal disease should also increase intake of vitamin A.
Vitamin A Deficiency
Vitamin A deficiency is rare, but the disease that results is known as
xerophthalmia. It most commonly occurs in developing nations usually due to
malnutrition. Since vitamin A is stored in the liver, it may take up to 2 years for
signs of deficiency to appear. 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.
Vitamin A toxicity
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 betacarotene,
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.
VITAMIN D
Vitamin D plays a critical role in the body’s use of calcium and phosphorous.
It works by increasing the amount of calcium absorbed from the small intestine,
helping to form and maintain bones. Vitamin D benefits the body by playing a
role in immunity and controlling cell growth. Children especially need adequate
Food Sources for Vitamin D
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 produces vitamin D in
response to sunlight.
RDA
The Recommended Dietary Allowance (RDA) for vitamin D appears as
micrograms (mcg) of cholecalciferol (vitamin D3). From 12 months to age fifty,
the RDA is set at 15 mcg. Twenty mcg of cholecalciferol equals 800 International
Units (IU), which is the recommendation for maintenance of healthy bone for
adults over fifty.
Exposure to ultraviolet light is necessary for the body to produce the active form
of vitamin D. Ten to fifteen minutes of sunlight without sunscreen on the hands,
arms and face, twice a week is sufficient to receive enough vitamin D. This can
easily be obtained in the time spent riding a bike to work or taking a short walk.
In order to reduce the risk for skin cancer one should apply sunscreen with an
SPF of 15 or more, if time in the sun exceeds 10 to 15 minutes.
Vitamin D Deficiency
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 may result in osteomalacia (muscle and bone weakness), and
osteoporosis (loss of bone mass).
amounts of vitamin D to develop strong bones and healthy teeth
The Tolerable Upper Intake Level (UL) for adults is 3,000 mcg RAE. It would
be difficult to reach this level consuming food alone, but some multivitamin
Recently published data introduces a concern that some adults and children may
be more prone to developing vitamin D deficiency due to an increase in
sunscreen use. In addition, those that live in inner cities, wear clothing that
covers most of the skin, or live in northern climates where little sun is seen in
the winter are also prone to vitamin D deficiency. Since most foods have very
low vitamin D levels (unless they are enriched) a deficiency may be more likely
to develop without adequate exposure to sunlight. Adding fortified foods to the
diet such as milk, and for adults including a supplement, are effective at ensuring
adequate vitamin D intake and preventing low vitamin D levels.
Vitamin D deficiency has been associated with increased risk of common
cancers, autoimmune diseases, hypertension, and infectious disease. In the
absence of adequate sun exposure, at least 800 to 1,000 IU of vitamin D3 may
be needed to reach the circulating level required to maximize vitamin D’s
benefits.
Vitamin D toxicity
The Tolerable Upper Intake Level (UL) for vitamin D is set at 100 mcg for people
9 years of age and older. 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 especially important that infants and young children do not consume excess
amounts of vitamin D regularly, due to their small body size.
