VITAMIN A, part 3: toxicity (with captions) (low audio) #8

There is a common belief that if something
is natural, it is good. Yet, nature can also produce harmful things,
and even good ones, in excess, may have deleterious effects. This is the case of vitamin A and other vitamins. When our body loses its ability to store and
eliminate the forms of vitamin A, called retinoids, consequences of toxicity begin to unfold. Fortunately we have several mechanisms to
prevent hypervitaminosis, but those who chronically use supplements should avoid products that
greatly exceed the recommended dietary allowance, as defined by the American Institute of Medicine
of The National Academies. Normally, the label of dietary supplements
display a table with nutrition facts. These contain a Daily Value, expressed as
a percentage that is based on the RDA. This should always be checked. But this value varies according to age and
gender. According to the IOM, the RDA is one of the
Dietary Reference Intakes and represents the average daily intake level which is sufficient
to meet the requirements of about 98% of healthy individuals. The RDA of vitamin A for men aged 14 and over
is 900 mcg/d. The RDA for women of the same age bracket
that are not pregnant nor lactating is 700 mcg/d. On the other hand, the Tolerable Upper Intake
Level is 3,000 mcg/d for both men and non-pregnant, non-lactating women aged over 18. This is important because some products are
manufactured with dosage forms that contain exactly this amount, or even higher quantities. However, these doses may be exceeded when
deficiency is present and treatment is necessary – in which case the dosage depends on the
individual’s age, symptoms, and concurrent illnesses – and higher amounts of vitamin
A may also be used for prevention in high-risk populations. When our levels of vitamin A exceed our body’s
ability to handle them, dysfunction of several organs ensue, mainly involving the nervous
and musculoskeletal systems, the liver, skin and mucous membranes. Possibly the main features of acute hypervitaminosis
A are related to intracranial hypertension, caused by increased pressure of the cerebrospinal
fluid, which surrounds the brain and spinal cord in the subarachnoid space, and also fills
the ventricular system (inside the brain). This phenomenon may generate vomiting, headache,
dizziness, drowsiness, blurred vision, and incoordination. Chronically, the skin may become dry, itchy,
and exfoliate. Dryness may also occur in the lips, nasal
mucosa and the eyes, leading to conjunctivitis. Nails get frail and hair loss is increased. Bones may grow and compress other structures,
such as the optic nerve, passing through its canal in the cranium. Some studies also suggest that the risk of
osteoporosis could be increased, and osteoporosis is an important risk factor for fractures,
especially in the elderly. Other signs include anemia, enlarged spleen
and liver, and also muscle and joint pain. However, the worst consequence of hypervitaminosis
A is related to pregnancy, since it can cause birth defects involving the cranium, and the
nervous and cardiovascular systems. Thus, pregnant women and those that may become
pregnant should be treated if they are deficient, but be wary of taking supplements and other
products that contain vitamin A. For example, retinoids, a synonym for vitamin A, are used
in the treatment of several dermatological conditions, such as acne. Isotretinoin is another name for the vitamer
13-cis-retinoic acid, and tretinoin is all-trans-retinoic acid. Therefore, these products are also teratogenic.

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