- Chemical Structure,
- Deficiency Disease,
- Other Effects,
- Other Members of the Vitamin B Complex
When Vitamin B was first discovered we did not realise that it was a complex group of different but related vitamins. We thought that it was a single chemical. This chemical was given the name “Nicotinic Acid” but some people might think that it was not good for you (nicotine from cigarette smoke is not good for you) so we decided to call it “Niacin”. It is also referred to as PP factor (Pellagra Preventing). You could call it Vitamin BVitamin B3. However, the standard text books seem to contradict each other with the numerical subscripts for the Vitamin B Complex so I prefer NOT using them.
Nicotinic Acid is water soluble. This is quite important because it may be lost when you cook your food by boiling it in water! It is also important because it cannot be stored in the body and must therefore be present in your diet to replace that which is lost in urine. Don’t worry about remembering the chemical structure for your “A” Level exams. It is more important for you to understand why a deficiency of this chemical causes pellagra.
Nicotinamide can be used instead of nicotinic acid. As you can see from these two structural formulae they are almost the same.
Humans do not have the ability to synthesise sufficient nicotinic acid, this means that it is an essential component of a balanced diet. Some mammals are able to synthesise this chemical so it is not an essential component of their diets. For example, dogs can synthesise nicotinic acid from the amino-acid tryptophan. This might be an essential amino-acid, but for dogs, nicotinic acid is definitely NOT a vitamin. Bacteria in our large intestines, the colon, may convert tryptophan into nicotinic acid; this means that we could survive if sufficient bacterial activity took place. Our intestinal bacteria would require 60 mg of tryptophan to synthesise 1 mg of nicotinic acid so don’t count on them.
Nicotinic Acid is found in milk, yeast, eggs. Here is a table of average values for the Nicotinic Acid content of a variety of foods. I have always thought that the two at the bottom of the table were dead boring. (I prefer cream in my coffee.)
FOOD Content ~ mg/100g
Meat Extract ~ 60.0
Marmite ~ 58.5
Roast Beef ~ 5.0
Sardines in Oil ~ 5.0
Kippers ~ 4.2
Wholemeal Bread ~ 3.5
Beer ~ 0.7
Boiled Cabbage ~ 0.15
Milk ~ 0.08
Pellagra is associated with a low standard of living. It is particularly prevalent; in areas where maize forms the staple diet. Maize has a very low content of nicotinic acid, furthermore, the proteins in maize are deficient in tryptophan.
The main deficiency disease caused by lack of nicotinic acid is “Pellagra” This disease affects epithelia and nervous system. It is caused by the accumulation of the intermediate products of respiration: this is because nicotinic acid is required for the synthesis of co-enzymes used by dehydrogenases. The symptoms of pellagra are dermatitis, diarrhoea and even mental disorder. You have been warned; make sure that you include this vitamin in your diet.
You should worry if you notice the following symptoms: nervousness, headaches, fatigue, mental depression, skin disorders, muscular weakness, and indigestion. Do remember that there are other causes for some of these symptoms.
Nicotinic acid is required by our cells for the synthesis of the co-enzymes used by dehydrogenase in tissue respiration. These are NAD and NADP (remember these from your work on tissue respiration?) If dehydrogenase does not function (it cannot do so without its co-enzymes) there will be an accumulation of various intermediates of tissue respiration. For example, succinic dehydrogenase is required to convert succinic acid into fumaric acid. The accumulation of these intermediates prevents normal tissue respiration, so how can cells obtain energy? The first cells to suffer from deficiency of nicotinic acid are the most active ones (nerve cells) and those which readily lose nicotinic acid because it is soluble in water (epithelia).
Problems also occur with the control of protein synthesis, the formation of acetyl-choline and the correct balance and formation of blood cells.
Other Members of the Vitamin B Complex
Thiamine (B1), Riboflavine (B2), Pyridoxine(B6), Pantothenic Acid, Biotin, Cyanocobalamin (B12).