Vitamin D-What, Where, When, How, Why?

Vitamins are not generally considered to be endocrine substance, but it is a organic dietary factors essential for healthy life. The term ‘ vitamin D ’ refers to two steroid like chemicals, namely ergocalciferol and cholecalciferol . Vitamin D is important for good health, growth and strong bones and may also help to prevent other diseases such as cancer, diabetes and heart disease. A lack of vitamin D is very common. Vitamin D is mostly made in the skin by exposure to sunlight.  A mild lack of vitamin D may not cause symptoms but can cause generalised aches and pains and tiredness. A more severe lack can cause serious problems such as rickets (in children) and osteomalacia (in adults), described below. Treatment is with vitamin D supplements. Some people are more at risk of vitamin D deficiency, and so are recommended to take vitamin D supplements routinely. These include all pregnant women, breast-fed babies, children under 5, and people aged 65 and over. Also, people who do not get much exposure to the sun, people with black or Asian skin types, people who do not go out in the sun and people with certain gut, liver or kidney diseases.  We have checked our own patients and found that 9/10 adults of South Asian origin are vitamin D deficient and something like 60% of our white patients are vitamin D deficient.  Most people present with aches and pains and tiredness.

What is vitamin D?
Vitamins are a group of chemicals that are needed by the body for good health. Foods that contain vitamin D include the following though many foods do not contain much vitamin D and exposure to the sun is a better source of vitamin D than foods. Vitamin D is a fat-soluble vitamin. Most foods contain very little vitamin D naturally , though some are fortified (enriched) with added vitamin D.  Foods that contain vitamin D include:
                -Oily fish (such as sardines, pilchards, herring, trout, tuna, salmon and mackerel).
                -Egg yolk.
                -Fortified foods (this means they have vitamin D added to them) such as margarine, some cereals, infant formula milk.

Action of Vitamin D
The 1,25 - (OH)2 -D 3 receptor belongs to a superfamily of nuclear hormone receptors, which bind to their ligand and alter transcription. The hormone travels in the bloodstream in equilibrium between bound and free forms. The latter form is freely able to enter cells, due to its lipophilic nature. The plasma 1,25 - (OH) 2 - D 3 - binding protein (DBP) recognizes the hormone specifi cally. 1,25 - (OH) 2 - D 3 binds to the nuclear receptor; the complex binds to specifi c hormone response elements on the target gene upstream of transcriptional activation sites, and new mRNA and protein synthesis result.
New proteins synthesized include osteocalcin, an important bone protein whose synthesis is suppressed by glucocorticoids. In the GIT, a calcium - binding transport protein (CaBP) is synthesized in response to the hormone – receptor activation of the genome.

Physiological actions of vitamin D

Bone-Vitamin D stimulates resorption of calcium from bone as part of its function to maintain adequate circulating concentrations of the ion. It also stimulates osteocalcin synthesis.
Gastrointestinal tract-1,25 - (OH) 2 - D 3 stimulates calcium and phosphate absorption from the gut through an active transport process. The hormone promotes the synthesis of calcium transport by enhancing synthesis of the cytosolic calcium – binding protein CaBP, which transports calcium from the mucosal to the serosal cells of the gut.
Kidney- 1,25 - (OH) 2 - D 3 may stimulate reabsorption of calcium into the tubule cells while promoting the excretion of phosphate. The tubule cells do possess receptors for vitamin D and CaBP.
Muscle-Muscle cells have vitamin D receptors, and the hormone may mediate muscle contraction through effects on the calcium fl uxes, and on consequent adenosine triphosphate (ATP) synthesis.
Pregnancy-During pregnancy, there is increased calcium absorption from the GIT, and elevated circulating concentrations of 1,25 - (OH) 2 - D 3 , DBP, calcitonin and PTH. During the last 6 months prior to birth, calcium and phosphorus accumulate in the fetus. The placenta synthesizes 1,25 - (OH) 2 - D 3 , as does the fetal kidney and bone. Nevertheless, the fetus still requires maternal vitamin D.
Other roles- Vitamin D may be involved in the maturation and proliferation of cells of the immune system, for example of the haematopoietic stem cells, and in the function of mature B and T cells.

Our main source of vitamin D is that made by our own bodies. 90% of our vitamin D is made in the skin with the help of sunlight.
Ultraviolet B (UVB) sunlight rays convert cholesterol in the skin into vitamin D. Darker skins need more sun to get the same amount of vitamin D as a fair-skinned person. The sunlight needed has to fall directly on to bare skin (through a window is not enough). 2-3 exposures of sunlight per week in the summer months (April to September) are enough to achieve healthy vitamin D levels that last through the year. Each episode should be 20-30 minutes to bare arms and face. This is not the same as suntanning; the skin simply needs to be exposed to sunlight.
So, vitamin D is really important for strong bones. In addition, vitamin D seems to be important for muscles and general health. Scientists have also found that vitamin D may also help to prevent other diseases such as cancer, diabetes and heart disease.

Who gets vitamin D deficiency?
Vitamin D deficiency means that there is not enough vitamin D in the body. Broadly speaking, this can occur in three situations:

1. Increased need for vitamin D
Growing children, pregnant women, and breast-feeding women.

2. Situations where the body is unable to make enough vitamin D
People who get very little sunlight on their skin are also at risk of vitamin D deficiency. This is more of a problem in the most northern parts of the world where there is less sun. In particular:
                 People who stay inside a lot or cover up when outside or use strict sunscreen
                 People with pigmented (dark coloured) skins and elderly people  
                 Some medical conditions can affect the way the body handles vitamin D.
                     People with Crohn's disease, coeliac disease, and some types of liver                                                     and kidney disease, are all at risk of vitamin D deficiency.
                 Vitamin D deficiency can also occur in people taking certain medicines -                                                  examples include: Carbamazepine, Phenytoin, prim done, barbiturates and some anti-HIV                    medicines
3. Not enough dietary vitamin D
Vitamin D deficiency is more likely to occur in people who follow a strict vegetarian or vegan diet, or a non-fish-eating diet.

How common is vitamin D deficiency?
It is very common. This is why we recommend a regular supplement to our patients.  A recent survey in the UK showed that more than half of the adult population in the UK had low vitamin D. This level is found to be greater in people who have dark skin.  In the winter and spring about 1 in 6 people has a severe deficiency. It is estimated that about 9 in 10 adults of South Asian origin may be vitamin D-deficient. Most affected people either don't have any symptoms, or have vague aches and pains, and are unaware of the problem.  80% of our Asian patients have been found to be deficient and 60% of our white patients have found to be deficient.

What are the symptoms of vitamin D deficiency?
Symptoms of vitamin D deficiency are tiredness or general aches.  Because symptoms of vitamin D deficiency are often very vague, the problem is often missed.

How is vitamin D deficiency diagnosed?
Vitamin D deficiency can be diagnosed by a blood test.  However, on balance if you have dark skin and live in the UK you should take supplements. It may be suspected from your medical history, symptoms, or lifestyle. A simple blood test for vitamin D level can make the diagnosis.

RECOMMENDATIONS – Your doctor will advise you if you have deficiency or insufficient vitamin D.  If you have a minor level of vitamin D deficiency we recommend patients buy vitamin D tablets equivalent to 10ug or 12.5ug.  Most are made from vegetables.   If you have been found to be deficient we would recommend you stay on this dose for life as treatment is often needed long-term because the cause of the deficiency, such as dark skin or not enough sunlight, is unlikely to be corrected in the future.  We have observed that it takes at least 6 months taking regular vitamin D for symptoms to resolve and the level of vitamin D to return to normal.  It should be noted that if you have severe deficiency the doctor may recommend that you take a higher dose of vitamin D for a limited time, often equivalent to 25ug for the first 3 months.  Please discuss this with your own doctor.  We recommend that patients buy vitamin D tablets as we are unable to prescribe vitamin D without calcium on the NHS and calcium prescriptions have been associated with increased kidney stones and it is for this reason that we recommend that our patients buy vitamin D.

Maintenance therapy after deficiency has been treated
The dose needed for maintenance maybe lower than that stated.  We advise patients to buy 10ug and take 2 a day.   When the body's stores of vitamin D have been replenished. maintenance treatment is often needed long-term, to prevent further deficiency in the future. This is because it is unlikely that any risk factor for vitamin D deficiency in the first place, will have completely resolved. The dose needed for maintenance may be lower than that needed to treat the deficiency.

Cautions when taking vitamin D supplements
Care is needed with vitamin D supplements in certain situations:
 1. If you are taking certain other medicines that can interact such as  Digoxin (for an irregular         heartbeat – atrial fibrillation),  Thiazide or diuretics (water tablets).                                                   
2. If you have medical conditions such as kidney stones, some types of                                                     kidney disease, liver disease or hormonal disease.
3. Vitamin D should not be taken by people who have high calcium levels.
4. You may need more than the usual dose if taking certain medicines such as Carbamezapine, Phenytoin. HRT or barbiturates. Multivitamins are not suitable for long-term high-dose treatment because the vitamin A which can be harmful in large amounts.

Are there any side-effects from vitamin D supplements?
It is very unusual to get side effects from vitamin D if taken in the prescribed dose. However, very high doses can raise calcium levels in the blood. This would cause symptoms such as thirst, passing a lot of urine, nausea or vomiting.

Prognosis (outlook) in vitamin D deficiency?
The outlook for vitamin D deficiency is usually excellent. Both the vitamin levels and the symptoms generally respond well to treatment. However, it can take time (months) for symptoms to resolve and for bones to recover.  Generally after 6 months of using Vitamin D tablets the patient feels a lot better and symptoms have improved.  This does not mean you need to stop taking the medication.  Vitamin D supplementation is for life.

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