Vitamin A

Vitamin A

23-03-2016
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What you can achieve by taking it

Better immune function

Vitamin A stimulates the immune system. Sufficient vitamin A intake supports the body in the fight against infections.

Skin health

Vitamin A helps keep the health of the epithelial tissues. There is no healthy and beautiful skin without vitamin A.

Sharp eyesight

Vitamin A and its provitamins, the carotenoids are essential for good eyesight.

Product name | Brand Properties Price
£ 8.27
£ 0.03/g.c.
£ 13.39
£ 0.13/tab.


Overview

It is well-known for long that some foods (like cod liver oil) have a positive impact on sight and eye function. However, the substance (vitamin A) that caused these effects was not discovered until 1913. The name vitamin A doesn’t refer to one chemical. There are several substances with identical or similar biological effects.

Substances with vitamin A-like effects:

  • Retinol ~ Vitamin A alcohol
  • Retinal ~ vitamin A aldehyde
  • Vitamin A2~ 3,4-Didehydroretinol
  • Provitamins ~ alpha-, beta-, gamma-carotene and other carotenoids of vitamin A activity (not all of them have these attributes).

In nature, vitamin A (retinol) is found in animal food sources, while beta-carotene, its most active provitamin can be found in bright red or yellow vegetable sources. Beta-carotene can break down to 2 vitamin A molecules in the body. However, this transformation is limited. The body can store an amount of vitamin A that is enough for about one year, mostly in the liver (this doesn’t mean that deficiency cannot occur sooner; it depends on how full the stocks were in the beginning). Retinol gets from the liver to the blood stream bound to transporter proteins. In case of insufficient protein intake, this mobility is inhibited. 70 to 90% of vitamin A is absorbed through the intestines. This percentage is lower in the case of carotenoids (only 20 to 50 per cent) and higher in the case of carotene supplements. Low or zero fat intake will worsen the absorption.

Vitamin A is inevitable for the activity of visual purple (rhodopsin), a light-sensitive receptor protein in the eyes. Vitamin A deficiency causes night blindness, i.e. insufficient adaptation of the eyes to darkness or changing light conditions. Long-term deficiency can cause blindness. Vitamin A is also essential for growth and, most probably, for bone development, too. Deficiency causes growth disorders or abnormal functioning of the sensory organs (tasting or smelling). Its most common effect is ensuring skin health. Actually, it also has a positive impact on other epithelial cells, namely the intestinal epithelium. This means, hypovitaminosis may also cause disorders in its functioning. Vitamin A derivatives are also used in medicine. For example, for 13-cis retinoic acid or isotretinoin, a substance that is used to treat acne, or etretinate, which can be used in the treatment of psoriasis. Side effects may include liver damage, muscle soreness or vomiting.

Why it is worth using

Everybody needs vitamin A to stay healthy and maintain good eyesight. This is especially true for athletes, because, in their case, a sufficient supply of antioxidants is even more important to ensure proper immune functions despite the high load they are constantly exposed to (and carotenoid provitamins are essential in this respect). It protects against infections (let them be bacteria, fungi or viruses) and helps the body overcome them. For example, it can be used to support the treatment of vaginal yeast infections. It is also used in the treatment of dry eyes; it helps prevent breast or lung cancer; may improve the condition of AIDS patients and can be useful in the treatment of melanoma, too. It also supports the healing of wounds. Supplementation can be especially important for individuals on low or moderate fat intake, especially if the diet is low on animal fats, since the richest vitamin A sources are high-fat animal sources.

Further benefits

It is inevitable for proper eyesight; deficiency may lead to hemeralopia (day blindness).

How to use it

Vitamin A requirement is usually indicated in international units (IU). But since it is also derived from carotenoids, the vitamin A activity of different chemicals varies, too. For this reason, the term retinol equivalent (RE) was introduced:

1 RE =

  • 1 mcg of retinol
  • 6 mcg of beta-carotene
  • 12 mcg of other carotenoids of vitamin A effects
  • 3.33 IU of retinol
  • 10 IU of beta-carotene

Supplements usually contain 5000 to 7000 IU. This is enough for healthy adults to maintain good health (women need about 800 mcg or 2664 IU of retinol, while men need about 3333 IU or 1000 mcg). There is no consensus in technical literature on accurate daily requirements or recommended amounts. Sometimes higher doses like 20,000-30,000 IU are used, mostly in the form of beta-carotene, since it transforms to vitamin A only to a limited extent, so it won’t be overdosed. Extremely high doses of carotene may cause skin discoloration (carotinaemia), which will cease when the dosage is reduced or suspended. The official recommendation is about 800 mcg or 2664 IU of retinol, and it is not recommended to exceed it unless advised by a professional. The vitamin A requirement of the body gets higher at times of considerable stress like sport, illnesses, infections, emotional traumas, anxiety or frequent alcohol consumption.

The body can tolerate amounts up to 10,000 IU. However, consuming more than 50,000 IU for a longer period of time (2 weeks or more) can be toxic. If you eat offal on a regular basis, you might overdose of vitamin A, especially if you take supplements, too. You better know that beef liver contains 43,900 IU/100 g, veal liver contains 22,500 IU/100 g and chicken liver contains 12,100 IU/100 g of vitamin A (exact quantities may vary). As a supplement you may take it in the form of a multivitamin. It is not recommended to take vitamin A in itself in high doses.

Timing: Since it is a fat soluble vitamin, the body can store it for a long time. Therefore, everyday intake is not necessary. If you take a supplement, take it with meals that contain fats.

Synergies

Vitamin E ensures better absorption, while protein and zinc are necessary for the proper mobility of vitamin A. It enhances the absorption of iron.

Natural sources

Liver, fish, egg yolks, milk and dairies are rich sources of vitamin A. It is found in higher concentration in high-fat foods. This means that a low-fat diet may lead to vitamin A deficiency.

Possible side effects

Since vitamin A is a teratogen (may disturb the development of an embryo or fetus), pregnant women should not exceed 10,000 IU per day and should only eat offal every now and then. The recommended daily amount is a maximum of 5000 IU. However, you should consult a doctor or nutritionist.

If more vitamin A is consumed than what the storage capacity of the liver can handle, that may cause problems in cellular metabolism. Consuming 50,000-100,000 IU for a longer period of time (2 weeks or more) can be toxic: vomiting, nausea, hair loss, weight loss, irregular periods or growth abnormalities may occur.

A higher intake may also entail a higher risk of osteoporosis. So, if you belong to a higher risk group because of your lifestyle or illness(es), you better opt for beta-carotene supplements.

Safety: It is safe if taken as per the recommendations.

Contraindication: None.

The history of vitamin A

It was discovered as early as the 1800’s that hemeralopia (day blindness) can be treated by cod liver oil. However, the substance that caused these effects was not discovered until 1913. The initial studies that lead to the discovery of this vitamin were conducted by two research groups (McCollum & Davis and Osborne & Mendel), nearly at the same time. Its chemical structure was described by Paul Karrer.

Q & A on vitamin A

I am expecting a baby. Can I take vitamin A supplements?


Pregnancy is one of the cases when higher vitamin A consumption entails significant risks. If you wish to have a healthy baby, you should not start vitamin supplementation without consulting your gynecologist or nutritionist.

Should I take vitamin A or Roaccutane to treat my severe acne?


Only if advised by a medical specialist. Both vitamin A and its derivatives can have side effects. It is expressly not recommended if you have liver problems or take liver damaging drugs (which is quite common among bodybuilders).

Bibliography


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