Vitamin D status is best measured by a blood test called 25-hydroxy vitamin D (25-OH D). In ng/mL: under 20 is deficiency, 20-29 is insufficiency, 30-100 is the target range. In community surveys from across India, including the Northeast, 70-90% of adults fall below 30 ng/mL despite available sunshine. The most common cause in Silchar is not absence of sun but absence of skin exposed to direct midday sun. Most deficiencies are corrected with weekly oral cholecalciferol for 8-12 weeks, then a small maintenance dose - guided by a follow-up test, not guesswork.
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Why a sunny region still has so much deficiency
Vitamin D is, oddly, more a hormone than a vitamin. Your skin produces it when UVB light hits a cholesterol-derived molecule called 7-dehydrocholesterol. Sounds simple - and in our ancestors, who worked outdoors with much of their skin exposed, it was. Modern life systematically blocks every step:
- Indoor work. An office worker or homemaker in Silchar may spend 90% of daylight hours indoors. Window glass blocks UVB almost entirely.
- Modest dress. Sari, salwar, kurta, dupatta - the body surface area routinely exposed to sun is small. Forearms and face alone are not enough.
- Skin pigmentation. Melanin acts as a natural sunscreen. South Asian and Northeast Indian skin types need roughly 3-6 times the sun exposure that lighter skin needs to produce the same vitamin D.
- Time of day. Effective UVB is only present roughly between 10 AM and 3 PM - exactly when most of us are at work or school.
- Sunscreen and pollution. SPF 30 blocks ~95% of UVB, and Silchar's air is not as pristine as it looks; particulate matter does block some UV.
- Diet. Vitamin D is naturally found in fatty fish, egg yolk, and sun-dried mushrooms - not staples in most Indian diets. Indian milk is not routinely fortified.
Stack four or five of those and a 25-year-old colleague who "goes to the market every day" still walks in with a 25-OH D of 12.
When to suspect a low level
Severe deficiency causes obvious bone disease - rickets in children, osteomalacia in adults. Insufficiency is much subtler and often presents as:
- Generalised body ache and muscle weakness, especially in the thighs and shoulders
- Bone pain in the low back, hips, ribs or shins (a useful clue: pressing the breastbone or shin reproduces the discomfort)
- Fatigue that does not match your sleep or workload
- Recurrent musculoskeletal injuries or fractures from minor trauma
- Hair fall and frequent infections (less specific, but commonly reported)
None of these symptoms is specific to vitamin D - they overlap with thyroid disease, anaemia, depression and many others. That is precisely why a blood test, not a guess, is the right way to confirm.
The 25-OH vitamin D test in plain English
The test measures 25-hydroxy vitamin D (also written as 25(OH)D, calcidiol). This is the storage form your liver makes after pulling raw vitamin D from skin synthesis or food. It has a long half-life of two to three weeks, which makes it an excellent gauge of your average vitamin D status over the past month or two.
What it is not: a single fasting blood draw, no special timing, no special preparation. Costs vary across India; at Optima Diagnostics it is offered as a stand-alone test and alongside other preventive tests. The closely related test - 1,25-dihydroxy vitamin D (calcitriol) - is the active form, but it does not reflect stores and is reserved for specific conditions like sarcoidosis or kidney disease. Most patients should not order it routinely.
What the numbers mean
< 10 ng/mL - severe deficiency. Often associated with bone pain, proximal muscle weakness and raised PTH and alkaline phosphatase. Needs prompt, higher-dose correction.
10-19 ng/mL - deficient. Standard correction therapy. Most working adults in Silchar who have never supplemented fall in this band.
20-29 ng/mL - insufficient. Worth correcting, especially if symptomatic or if you have osteoporosis, diabetes or autoimmune disease.
30-50 ng/mL - desirable. The bone, muscle and immune benefits of vitamin D plateau in this range.
> 100 ng/mL - high. Almost always due to over-supplementation. Stop supplements and recheck in 4-6 weeks. Toxicity is rare below 150 ng/mL but the trajectory matters.
How to correct a low result
Correction has two phases: loading (to fill the empty tank) and maintenance (to keep it full).
A widely used, well-tolerated Indian regimen for adults with a 25-OH D below 20 ng/mL is cholecalciferol 60,000 IU orally once a week for 8 weeks, then a recheck. For levels between 20 and 29, a 6-week course is often enough. Severely deficient (< 10) patients may need 12 weeks of weekly loading and a calcium-and-PTH check to rule out coexisting issues.
A few tips your pharmacist may not mention:
- Take the dose with a meal that contains fat - it is a fat-soluble vitamin and absorption roughly doubles when taken with food.
- Buy cholecalciferol (vitamin D3), not ergocalciferol (D2). D3 corrects levels faster and is more available in India.
- Liquid sachets dissolved in milk are practical for the elderly and for children. Tablets work just as well for most adults.
- Calcium correction is only needed if dietary calcium is low or if PTH is elevated. Pop-prescribing calcium to everyone with low vitamin D is a habit best avoided.
Staying topped up after correction
Once corrected, most adults stay in the desirable range on:
- 2,000 IU of cholecalciferol daily, or
- 60,000 IU once a month, or
- Enough daily sun on bare arms and legs - in our latitude, roughly 20-30 minutes between 10 AM and 2 PM, 4 days a week, without sunscreen on the exposed area. The face does not contribute much; it is too small a surface.
Recheck once a year. If a follow-up test in three months shows you have not corrected on the standard regimen, consider malabsorption (coeliac disease, IBD), liver or kidney disease, or simply non-adherence. We have a separate guide on the sensible annual health check-up panel that includes vitamin D for adults over 40.
One sentence to remember: in Silchar, the bigger problem is rarely that vitamin D is unavailable - it is that we are not exposed to it. Test once, correct properly, then make small lifestyle changes that prevent the next deficiency.
Frequently asked questions
What is the normal range for vitamin D?
In ng/mL: less than 20 is deficiency, 20-29 is insufficiency, 30-100 is the desirable range. Values above 100 should prompt stopping supplements and a follow-up.
Do I need to fast for a vitamin D test?
No. The 25-OH vitamin D test does not require fasting and can be done at any time of day.
How long does it take to correct deficiency?
Most adults reach the desirable range in 8 to 12 weeks of weekly 60,000 IU supplementation, followed by daily or weekly maintenance.
Why is deficiency common in sunny regions?
Indoor lifestyles, modest dress, darker skin pigmentation, sunscreen use, pollution and a diet low in fortified foods all reduce vitamin D synthesis and intake.
How often should I recheck once corrected?
Once a year for most adults on stable maintenance. Sooner if you stop supplements, develop new symptoms, or have a condition affecting absorption.
This article is for general education. Specific supplementation regimens should be confirmed with your treating doctor, particularly if you have kidney disease, sarcoidosis or are taking other medications.
