فيتامين  VITAMINE  B12

-         فيتامين يحتوي على الكوبلت ويعرف بكوبال امين COBALAMINE .

-         يتم ارتباط فيتامين B12 بانترينسك فاكتورintrensic factor بالمعدة ويحتاج الي وسط حامضي .

-         يتم امتصاص هدا المركب بالجزء الاخير من الامعاء الدقيقة ودلك بسبب وجود بوابات خاصة لامتصاص هدا المركب .

#  نقص فيتامينB12 :

-         هدا الفيتامين حيواني المصدر( الكبد – الكلى – اللحوم ) .

-         الاحتياجات  اليومية للشخص العادي -1-2 microgram/day-  .

-         احدوث اعراض النقص  يجب ان تمر فترة ثلاث سنوات بسبب المخزون الكبير في الجسم خاصة الكبد .

# اسباب النقص :

 الاشخاص الدين يتغدون على الخضروات فقط –true vegans- .

-         غياب intrinsic factor  بسبب- ضمور المعدة – عملية جراحة المعدة غياب خلقي .

-         مرض الجزء الاخير للامعاء الدقيقة مثل CHRON'S  او عمليات استئصال .

-         الاصابة بالطفيليات  او الجراثيم البكثيرية او وجود ناسور مابعد الجراحة .

THE ADDISONIAN PERNICIAS ANAEMIA

فقر الدم بسبب نقص VIT B12

-         نتيجة فشل المعدة بافراز العامل الرابطthe intrinsic factor

-          نادر الحدوث قبل سن الثلاثين .

-         يصيب النساء اكثر من الرجال .

# الباثولوجي :

-         فشل بناء الاحماض النووية بالنخاع العظمي .

-         وجود كريات الدم الحمراء الغير تامة النضج .

-         وجود مخلفات تكسير كريات الدم الغير صالحة في الطحال والكبد والكلى والنخاع العظمي .

-         جدار المعدة رقيق وضامر .

-          في الحالات المتأخرة تلتهب بعض الظفائر العصبية بالحبل الشوكي –SCPD-

# الاعراض  :

-         تبداء الاعراض تدريجياً .

-         يكون فقر الدم بدرجة كبيرة  واعراضها المعروفة .

-         التهاب واحمرار اللسان .

-         اسهال على شكل نوبات .

-         يفقد المريض الوزن بالرغم من الاكل الجيد .

-         تضخم الطحال .

-         تنمل الاصابع باليدين والقدمين –Subacute Compined Posterior Degeneration - -.

-         انعدام الخصوبة خاصة عند المرارة ..

# التشخيص :

تحليل الدم :

-         وجود كريات الدم الحمراء كبيرة الحجم macrocytic .

-         عدم تساوي  احجام كريات الدم anisocytosis .

-         احتواء كريات الدم على نواة وهدا غير طبيعي neucleatedRBC .

-         نقص كريات الدم البيضاء neutropenea .

-         نقص الصفائح بالدم trhombocytopenea .

# العلاج :

1- hydroxocobalamin   1000 microgram  مرتين في الاسبوع الاول.ثم مرة واحدة اسبوعيا الى ان يتعدل التحليل .

2- بسبب زيادة  انتاج كريات الدم يتم استنزاف مخزون الحديد عليه يجب اعطاء ferrus sulphat 2mg t.i.d. .

3- يجب اعطاء الفوليك اسيد بسبب استنزاف المخزون بالجسم .ولتفادي المضاعفات التي يمكن ان تحدث .

نقص الفوليت  THE FOLIC ACID

1-     يوجد الفوليك اسيد في الاوراق الخضراء واللحوم .

2-     ينشاء النقص من قلة الاكل الدي يحتوي على الفوليت .

3-     مرض الجزء العلوي من الامعاء الدقيقة مثل cealiac disease –tropical sprue –resection .

4-     زيادة استهلاك الجسم للفوليت مثل حالات الاورام 

5-     الحمل والرضاعة

6-     اخد بعض الادوية مثل methotrexate  توقف انتاج فيتامين الفوليت .

7-      ادوية الصرع .

د.ناصرحبارات

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Vitamin B12 is a member of the vitamin B complex. It contains cobalt, and so is also known as cobalamin. It is exclusively synthesised by bacteria and is found primarily in meat, eggs and dairy products. There has been considerable research into proposed plant sources of vitamin B12. Fermented soya products, seaweeds, and algae such as spirulina have all been suggested as containing significant B12. However, the present consensus is that any B12 present in plant foods is likely to be unavailable to humans and so these foods should not be relied upon as safe sources. Many vegan foods are supplemented with B12. Vitamin B12 is necessary for the synthesis of red blood cells, the maintenance of the nervous system, and growth and development in children. Deficiency can cause anaemia. Vitamin B12 neuropathy, involving the degeneration of nerve fibres and irreversible neurological damage, can also occur.

Functions

Vitamin B12's primary functions are in the formation of red blood cells and the maintenence of a healthy nervous system. B12 is necessary for the rapid synthesis of DNA during cell division. This is especially important in tissues where cells are dividing rapidly, particularly the bone marrow tissues responsible for red blood cell formation. If B12 deficiency occurs, DNA production is disrupted and abnormal cells called megaloblasts occur. This results in anaemia. Symptoms include excessive tiredness, breathlessness, listlessness, pallor, and poor resistance to infection. Other symptoms can include a smooth, sore tongue and menstrual disorders. Anaemia may also be due to folic acid deficiency, folic acid also being necessary for DNA synthesis.

B12 is also important in maintaining the nervous system. Nerves are surrounded by an insulating fatty sheath comprised of a complex protein called myelin. B12 plays a vital role in the metabolism of fatty acids essential for the maintainence of myelin. Prolonged B12 deficiency can lead to nerve degeneration and irreversible neurological damage.

When deficiency occurs, it is more commonly linked to a failure to effectively absorb B12 from the intestine rather than a dietary deficiency. Absorption of B12 requires the secretion from the cells lining the stomach of a glycoprotein, known as intrinsic factor. The B12-intrinsic factor complex is then absorbed in the ileum (part of the small intestine) in the presence of calcium. Certain people are unable to produce intrinsic factor and the subsequent pernicious anaemia is treated with injections of B12.

Vitamin B12 can be stored in small amounts by the body. Total body store is 2-5mg in adults. Around 80% of this is stored in the liver.

Vitamin B12 is excreted in the bile and is effectively reabsorbed. This is known as enterohepatic circulation. The amount of B12 excreted in the bile can vary from 1 to 10ug (micrograms) a day. People on diets low in B12, including vegans and some vegetarians, may be obtaining more B12 from reabsorption than from dietary sources. Reabsorption is the reason it can take over 20 years for deficiency disease to develop in people changing to diets absent in B12. In comparison, if B12 deficiency is due to a failure in absorption it can take only 3 years for deficiency disease to occur.

Dietary Sources

The only reliable unfortified sources of vitamin B12 are meat, dairy products and eggs. There has been considerable research into possible plant food sources of B12. Fermented soya products, seaweeds and algae have all been proposed as possible sources of B12. However, analysis of fermented soya products, including tempeh, miso, shoyu and tamari, found no significant B12.

Spirulina, an algae available as a dietary supplement in tablet form, and nori, a seaweed, have both appeared to contain significant amounts of B12 after analysis. However, it is thought that this is due to the presence of compounds structurally similar to B12, known as B12 analogues. These cannot be utilised to satisfy dietary needs. Assay methods used to detect B12 are unable to differentiate between B12 and it's analogues, Analysis of possible B12 sources may give false positive results due to the presence of these analogues.

Researchers have suggested that supposed B12 supplements such as spirulina may in fact increase the risk of B12 deficiency disease, as the B12 analogues can compete with B12 and inhibit metabolism.

The current nutritional consensus is that no plant foods can be relied on as a safe source of vitamin B12.

Bacteria present in the large intestine are able to synthesise B12. In the past, it has been thought that the B12 produced by these colonic bacteria could be absorbed and utilised by humans. However, the bacteria produce B12 too far down the intestine for absorption to occur, B12 not being absorbed through the colon lining.

Human faeces can contain significant B12. A study has shown that a group of Iranian vegans obtained adequate B12 from unwashed vegetables which had been fertilised with human manure. Faecal contamination of vegetables and other plant foods can make a significant contribution to dietary needs, particularly in areas where hygiene standards may be low. This may be responsible for the lack of aneamia due to B12 deficiency in vegan communities in developing countries.

Good sources of vitamin B12 for vegetarians are dairy products or free-range eggs. ½ pint of milk (full fat or semi skimmed) contains 1.2 µg. A slice of vegetarian cheddar cheese (40g) contains 0.5 µg. A boiled egg contains 0.7 µg. Fermentation in the manufacture of yoghurt destroys much of the B12 present. Boiling milk can also destroy much of the B12.

Vegans are recommended to ensure their diet includes foods fortified with vitamin B12. A range of B12 fortified foods are available. These include yeast extracts, Vecon vegetable stock, veggieburger mixes, textured vegetable protein, soya milks, vegetable and sunflower margarines, and breakfast cereals.

Required Intakes

The old Recommended Daily Amounts (RDA's) have now been replaced by the term Reference Nutrient intake (RNI). The RNI is the amount of nutrient which is enough for at least 97% of the population.

Reference Nutrient Intakes for Vitamin B12, µg/day. (1000 µg = 1mg)

Pregnant women are not thought to require any extra B12, though little is known about this. Lactating women need extra B12 to ensure an adequate supply in breast milk.

B12 has very low toxicity and high intakes are not thought to be dangerous.

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