India, authentic studies on the normal values of Vit

India, though a sunshine country, it is
reported that prevalence of Vit D (D3) deficiency is not only significant to the
extent of 85-90% but is also widespread. 
Vit D is also known as Cholecalciferol.
Unfortunately, we are unable to find authentic studies on the normal values of
Vit D3 in Indian population.  The studies
that are available have a small sample size and only longitudinal studies are
carried out.  There is no cross sectional
studies of normal Vit D3 levels in Indian population with sufficient sample
size, to make it statistically significant.

Unfortunately, the definition of normal
values for Vit D varies rather widely. 
In India, most of the laboratories report Vit D levels as deficient,
insufficient, sufficient and toxic.   Accordingly, serum levels of 25(OH) D less
than 10ng/mL is considered deficient, between 11 to 30 as insufficient, between
30 ng/mL to 100 ng/ml sufficient and above
100 ng/mL as toxic.  However, these are
western values, and its relevance to Indian population is not determined.  Again the significance of values deficient
and insufficient is also not determined. 
There is no unanimity amongst experts about normal levels of Vit D as limits
by IOM (Institute of Medicine) and those given by U S Endocrine society are
quite different as mentioned in table:4.

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It is perhaps necessary to note that
before starting therapy for severe Vit D deficiency, it is necessary to evaluate
the status with respect to Calcium, Phosphorus and PTH levels.Measurements
of Vit D levels:The assays of Vit D3 are performed by 4
methods: (a) High Performance Liquid Chromatography (HPLC), (b) tandem mass
spectrometry; (c) Radio immunoassays using monoclonal antibodies; (d)
chemiluminescent protein binging assay. 
Most of the laboratories in India use this chemiluminescent protein
binging assay method.Sources
of Vit D:Most important source of Vit D is
Sunlight, especially exposure of the skin to UVB radiation of the sunlight, and
less than 10-15% from dietary sources. 
The sunlight is composed of EMR of varying wavelengths ranging from long
lambda (IR) to short UVB radiation. The sunlight that reaches the earth has 90%
UVA radiation where as only 7-10% is UVB radiation. It is UVB radiation that
produces Vit D in skin. The production of Vit D in the skin is affected by time
of the day, year, latitude, altitude and prevailing weather conditions where we
live. Because of the direct sunlight (angle at which the sunlight hits the
ground—angle of incidence) is high compared to what it is in western countries
(-differences in latitudes at which our country and western countries are). Hence
UVB rays hit more directly, our country enjoys more UVB advantage over western
countries. The disadvantage of UVB light is possible development of skin cancer
but in dark skinned people the risk of this and melanoma is very little.  Remember that children have greater capacity
to produce Vit D compared to old people and hence require less exposure. Excessive
exposure to UVB does not lead to toxicity of Vit D.  People have tendency to use sun creams to
protect skin. Sun creams filter out UVB rays which leads to inadequate
availability of UVB rays for Vit D production through skin. This brings the
vital question, given all favourable conditions, why Vit D deficiency and
insufficiency is so common in our country. Or has it to do with poor Calcium
intake in diet or some PTH abnormalities? Or has to do with Vit D receptors?Literature ReviewCupisti, et al. (2015)
discussed in the paper about which factors were associated with vitamin D
deficiency. They have considered a group of 405 patients who have chronic
kidney disease with stage 2 to stage 4 living in Italy. They observed that
66.4% patients had deficiency and 16.5% patients had insufficiency of vitamin
D. Univariate analysis showed that vitamin D was negatively related to
age, parathyroid hormone (PTH), protein, and Charlson index, while positively
related to hemoglo­bin level. Multiple regression analysis showed that all
factors were associated except age and PTH. No relation was found between renal
function and vitamin D deficiency.100 consecutive patients out of 405 patients
were given 1000 IU supplements of vitamin D once a week for 12 months. Oral
vitamin D supplements reduced PTH serum level. So as a regular practice in CKD
patients, vitamin D supplements were recommended. Tokmak, et al. (2008) conducted study
between May 2004 to June 2006 on 64 hemodialysis patients (26 females and 38
males) of a German outpatient centre. It was observed that majority of hemodialysis
patients have vitamin D deficiency.  The
study was divided in to two phases: replenishment and maintenance. During the
replenishment phase, patients were given 20000 IU of cholecalciferol, in a form
of capsule, once a week for 9 months (till feb, 2005). From these 64 patients,
59 reached to maintenance phase. These 59 patients were randomized in treated
group (30 patients) and untreated group(29 patients). 20000 IU of cholecalciferol
once a month for next 15 months (March 2005 to May 2006) was given to the
patients of treated group. Finally analysis was done on 23 patients of treated
group and 19 patients of untreated group. 57% of the patients achieved
recommended levels. However additional study is required to decide ideal dosage
of vitamin D to achieve and maintain vitamin D levels in the majority of
patients.    Data
Collection and Data description: We have collected data from different
laboratories and doctors from Ahmedabad, Surat and Vadodara. But following
points should be kept in mind while making any general statement. Ø  Majority
of the data are due to the suggested blood test following some health problems.
Very few observations are from free check up camp. Ø  For
many cases observations were given as > some value, in those cases for the
sake of analysis we have taken next integer value as the observed value,
therefore instead of mean we suggest to observe median as the measure and hence
for inference nonparametric techniques are
used.Ø  In
the Ahemdabad data neither sex nor the age are specified therefore we tried to
identify the sex from the names. So there chances of
mistake to identify the sex as some names may be common for both male and
female. Whereas in data from Surat and Vadodara, sex of child is not
mentioned, so it is not possible to merge the data for even sex wise study or
we have to drop the data of child from Surat and Vadodara if we want to include
Ahemdabad data. But again in Ahemdabad data age is not mentioned so we do not
know actually how many of them are children. In
this situation, to have a logical comparison, we have used Ahmedabad data only
for aggregate analysis and not for sex wise and age wise analysis. Ø  For
all the categories (sex wise as well as age wise) common limits are used.

Ø   Number of data is displayed in the following
table: 1. From these data, we have prepared 3 age categories and three sex
categories. Then using different limits of D3 level in blood by (1) regular
limits used by the laboratories in India (2) suggested by IOM and  (3) Suggested by U S Endocrine society, we
have compared the respective descriptive & inferential statistics and