Fat-soluble vitamins Part I: Focus on vitamins A and D
If we take a look at different vitamins, we come up with a total of 13. Everyone knows vitamins as health-promoting and necessary components of our food. But why are they so important for a healthy life? What can vitamins do? In what quantities should we take them? What happens if you take too few vitamins? We would like to answer all these questions in the following.
Go to the end of the article for the short version!
Fat-soluble vitamins: Special absorption and storage in special places
Technically, these chemical compounds are categorised into two main groups: Fat-soluble and water-soluble vitamins. First, let’s look at the fat-soluble class of these substances. The main characteristic of fat-soluble vitamins is that these substances can and even must be absorbed together with food lipids. Absorbed by the cells of the small intestine, these substances are then transported via the lymphatic system, from where they enter the blood system. Finally, these vitamins are transported via the bloodstream to special places in the body where they are stored. When needed, the body can access these “stored” vitamins by releasing them.
Long-term overdose threatens accumulation
Because of their storage capacity, this category of vitamins is at risk of accumulating if too much is taken. Accumulation is the accumulation of certain substances in the body. The consequences are an excessive mechanism of action of the accumulated substance and, depending on the type of substance, also toxic consequences. Consequently, the potential for possible side effects in the case of an overdose of fat-soluble vitamins should not be underestimated. The fat-soluble vitamins include four vitamins: A, D, E and K.
We will now take a closer look at the two most popular representatives, vitamins A and D.
Vitamins A and D: Multiple functions
Vitamin A is normally ingested in the form of beta-carotene. Orange vegetables and fruit are particularly good sources. At the same time, three forms of vitamin A are distinguished that can be formed from beta-carotene: Retinal, Retinol and Retinoic acid. Each individual form has its own tasks in the human organism. Retinal primarily serves the visual process, retinoic acid influences our genes, and retinol protects our skin and mucous membranes and also ensures the development of the skeleton.
Vitamin D, on the other hand, is synthesised up to 50 % from cholesterol under the influence of UV radiation in our own skin. Foods such as cod liver oil or egg yolk also contain this valuable vitamin. The functions of vitamin D are far-reaching: it is involved in the balance of calcium and phosphate, strengthens the bones, influences the insulin secretion of the pancreas, ensures proper cell division of the skin and activates and strengthens our immune system.
It is essential to observe the daily dose of vitamins A and D.
Given the large number of tasks and functions of these two vitamins, it is understandable that the question arises as to how much of these substances our body actually needs on a daily basis. Adolescents and adults need 20 micrograms of vitamin D per day. This corresponds to 800 IU*. However, since vitamin D is the only vitamin that can be synthesised independently in the body, this guideline value only applies to cases in which this so-called endogenous synthesis does not occur. If, on the other hand, the body’s own synthesis is optimal, especially in the summer months when there are many hours of sunshine, there is no need for external substitution. However, attention should always be paid to a sufficient vitamin D level. Especially since more than one billion people worldwide suffer from a vitamin D deficiency. Moreover, such a deficiency is often associated with numerous diseases such as cancer, caries or autoimmune diseases.
The daily requirement of vitamin A differs for women and men. Men should take in about 1 milligram and women 0.8 milligram daily. In this context, 100 grams of spinach already contribute 0.6 milligrams of vitamin A.
An undersupply of vitamin A and D can lead to a wide variety of diseases.
Adherence to the minimum daily intake of vitamins A and D is necessary to avoid hypovitaminosis (= vitamin deficiency) and its consequences.
A vitamin A deficiency often leads to hemeralopia (= night blindness) in the first instance. If the deficiency lasts longer, however, there is a risk of xerophthalmia, a hornification of the cornea of the eye. The consequences are burning eyes, foreign body sensation and inflammation. There is also the possibility of male infertility.
A vitamin D deficiency manifests itself in particular by the fact that calcium absorption in the intestine is reduced and more calcium is released from the skeletal system to compensate. This results in a mineralisation disorder of the bone. In young growing patients, i.e. especially in children and adolescents, deformities of the skeleton often develop (in this respect one speaks of the disease “rickets”). Ultimately, a vitamin D deficiency poses the risk of osteoporosis and osteomalcia (= softening of the bones). Both osteoporosis and osteomalcia involve the risk of rapid bone fractures and possible complications depending on age and the severity of the bone fracture.
Possible consequences of overdose
As already mentioned above, fat-soluble vitamins are stored in the body, and so are vitamins A and D. Ultimately, overdosed vitamins have a toxic (= poisonous) effect on the body. Particularly in the case of an acute overdose of vitamin A, headaches, nausea and dizziness occur. If too much vitamin A is taken over a longer period of time, hair loss and skin dehydration can be the result. An overdose of vitamin D also causes nausea and dizziness. On the other hand, taking too much in the long term leads to calcification in the body, especially of the liver and kidneys.
To the point:
1. There are 13 different vitamins. Vitamins A, D, E and K are fat-soluble vitamins.
2. Fat-soluble vitamins are absorbed with dietary fats in the intestine and then stored in special places in the body.
3. If fat-soluble vitamins are overdosed, especially over a longer period of time, there is a risk of an accumulation of these substances and thus toxic consequences for the body.
4. Vitamins A and D have important functions (especially immune system) in our biological system and should therefore be supplied in sufficient amounts. 5. Especially in the case of vitamin D, care should be taken to ensure sufficient intake, as a large number of people worldwide suffer from a deficiency.
6. If too few vitamins A and D are consumed, there is a risk of contracting various diseases. A vitamin A deficiency leads in particular to night blindness and keratinisation of the eyes. Vitamin D deficiency, on the other hand, promotes bone diseases such as osteomalacia and osteoporosis, which increases the risk of skeletal damage.
* IU = International Unit: Medical unit of measurement for medicinal products.
Text sources:
(1) Niestroj, Praxis der orthomolekularen Medizin, 2nd edition, 2000.
(2) Grimm et al, Pocket Atlas of Nutrition, 8th edition, 2020
(3) https://www.dge.de/wissenschaft/referenzwerte/vitamin-d/
(4) Holick, The vitamin D deficiency pandemic: Approaches for diagnosis, treatment and prevention, 2017.
(5) https://www.dge.de/wissenschaft/referenzwerte/vitamin-a-b-carotin/
(6) Leitzmann et al., Nutrition in Prevention and Therapy, 2nd edition, 2003
(7) Dual Series, Internal Medicine, 2001.
Image sources:
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