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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