Fat Soluble Vitamins include vitamins A, D, E and K. As a general rule the suffix "-ol" infers a fat soluble compound; for example: calciferol contains vitamin D.
In order to get sufficient quantities of the fat soluble vitamins one must be ingesting and properly absorbing dietary fat. Any disease which affects fat absorption will also compromise absorption of vitamins A, D, E and K. Fat malabsorption is associated with Celiac disease, Crohn’s disease, Cystic Fibrosis, liver disease and cirrhosis and some pancreatic conditions. Tumours affecting the liver or bowels, or surgical procedures to, or removing parts of the lower digestive tract can also significantly impair fat and fat soluble vitamin absorption.
There are two types of vitamin A, those found in animal foods is preformed vitamin A or retinol. It is the most active form of vitamin A. In plant foods there is provitamin A, also known as carotenoid. The body must convert this and is not very efficient at doing so. Not all carotenoids are convertible into vitamin A, however many that aren’t, do function as anti-oxidants (lycopene for example) and are important inclusions in the diet for this reason.
Vitamin A has numerous roles in the body, not only vision. It is also important for bone growth and a role of cellular processes. The immune system requires vitamin A for proper function and the linings and membranes of the body need vitamin A to remain healthy.
Animal foods are the richest and most readily useable sources of vitamin A. Liver in particular, as well as dairy products are rich sources of vitamin A. The best plant sources include bright or dark coloured vegetables such as carrot, spinach, cantaloupe, apricot, mango, peas and capsicum.
In developed countries vitamin A deficiency is generally associated only with very strict diets or alcoholism and liver cirrhosis. It is however a serious problem in developing countries, leaving immune systems weak, and membranes of the body dry and brittle. This leads to fatal cases of measles, pneumonia and other infections.
A more common problem in developed countries is vitamin A toxicity. As a fat soluble vitamin, vitamin A can be stored in the liver; it is very stable and can be held for long periods. Chronic high intake can therefore result in toxicity. Increasing anecdotal evidence links high vitamin A, even in acute cases to birth defects. People who are zinc deficient are also at higher risk of toxicity as they are able to store vitamin A, but have trouble releasing it from the liver. As with all fat soluble vitamins, people with fat malabsorption disorders are at risk of vitamin A deficiency. Vegans may also be at risk of vitamin A deficiency as plant sources are not as rich as animal.
A microgram = µg or mcg
A milligram = mg
1000 micrograms (µg) is equal to 1milligram (mg)
Vitamin A supplements are rarely necessary in developed countries. They may in fact do more harm than good due to toxicity. In fact, beta-carotene supplements are strongly discouraged as they appear to increase cancer risk, but this is only in populations with adequate vitamin A intake and does not apply to developing countries. There is new research suggesting that chronic excess vitamin A can promote osteoporosis by hampering calcium absorption by inhibiting the production of vitamin D. Beta-carotene does not appear to have this effect, so eating fruits and vegetables high in provitamin A appears safe.
Symptoms of "chronic hypervitaminosis A" include:
- Birth defects
- Liver diseases
- Bone demineralisation
- Central nervous system disorders
Symptoms of acute toxicity include:
- Gastrointestinal upset: nausea and vomiting
- Neurological symptoms: impaired vision, headache, dizziness and muscular weakness
Some anti-acne treatments, such as Roaccutane contain high levels of synthetic retinoids and should never be taken if pregnant or if planning pregnancy. They should be limited to the most severe cases of acne and dietary vitamin A intake may need to be adjusted accordingly.
Vitamin D comes in three isoforms, the most active being calciferol, or Vitamin D3. In the body it is enzymatically altered in the liver and kidneys to form 1, 25 dihydroxy vitamin D. This active form functions as a hormone, telling the intestine to increase calcium absorption and also playing a role in the balance of calcium and phosphorus in the blood. Vitamin D is essential for proper bone and tooth mineralisation and deficiency can result in Ricketts and osteomalacia. It also has important functions within the body’s individual cells.
Vitamin D is actually quite easy to get, 10-15 minutes of exposure to ultra violet radiation (sunlight) three times a week is sufficient to induce the skin to synthesise all your body’s vitamin D. Darker skin is less efficient at this conversion than fair, however, strict dress codes in some countries and ethnic groups should not generally impair vitamin D synthesis but slightly longer exposure may be required if only hands, feet and face are exposed. Food sources are generally products fortified with the vitamin, such as milk, margarine, bread and cereals. The amount of fortification will vary from country to country. The richest natural sources are fatty fish, such as salmon, mackerel and tuna. Eggs also have a small amount of vitamin D.
Vitamin D deficiency is most commonly seen in people with kidney diseases, liver diseases or digestive illnesses such as Celiac disease, irritable bowel syndrome and acute diarrhoea. Kidney and liver diseases can hamper conversion of dietary vitamin D to its active form while bowel disorders can limit absorption of the vitamin in the first place. Prolonging exclusive breastfeeding (breast milk only and no foods) is one of the most common causes of vitamin D deficiency and Ricketts in infants and toddlers. Older people are also at greater risk of vitamin D deficiency as they are less efficient at synthesising and converting vitamin D. In colder climates with less sunlight hours, exposure to sun is less likely to supply vitamin D in sufficient quantity. As with all fat soluble vitamins, people with fat malabsorption are at risk of deficiency.
There are actually 8 different vitamins in the vitamin E family, referred to as tocopherols. Alpha-tocopherol is the most active, but all have some degree of potency in humans. Vitamin E is best known as an antioxidant, and in this role may help inhibit cellular damage that can set off the chain of events that result in tumour development. It also appears to function in the immune system, as well as within individual cells.
The best source of vitamin E is found in plant oils (vegetable and nut). Less rich sources include green vegetables. Vegetarians and vegans tend to have good vitamin E intake, but diets high in meats and animal fats can often be lacking.
Vitamin E deficiency is quite rare and most likely secondary to an illness, such as a genetic enzyme deficiency or, more commonly, in babies born very prematurely at very low weights, under 2kg. Symptoms are predominantly neurological; muscle weakness, nerve degeneration and poor nervous system function in general. Muscle fatigue and blindness can also occur. A person who is zinc deficient is also at increased risk of hypovitaminosis E as are people with fat malabsorption disorders.
Vitamin E toxicity is not as widely studied or understood as other vitamin toxicities. Symptoms may include bleeding problems as blood coagulation is impaired. The TUL for vitamin E should not be exceeded. People with clotting problems, or who are on medications to improve clotting, or limit clotting should seek advice on their vitamin E intake.
Vitamin K is also known as phylloquinone. It is essential for blood clotting (in contrast to vitamin E which thins the blood). Vitamin K is also required for good bone and kidney health and function. The human body cannot synthesise its own Vitamin K. However, about half a person’s daily requirement of vitamin K can be provided by the bacteria that live in the bowel.
Vitamin K may be found in high quantity in green leafy vegetables, including spinach, lettuce and cabbage. Other rich sources include broccoli and cauliflower, soy beans and wheat bran. Beef liver is the best animal source.
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