Vitamin D Deficiency in a Sunny Country: Why Indians Keep Testing Low

India sits between 8 and 37 degrees north, gets punishing sun for most of the year, and returns some of the highest vitamin D deficiency rates recorded anywhere. Survey after survey across Indian cities puts the proportion of adults below the sufficiency threshold somewhere between seventy and ninety percent. Doctors in Delhi and Chennai find it in people who work outdoors.

This looks like a paradox and it is not one. Once you understand what actually has to happen for sunlight to become vitamin D, the numbers stop being surprising — and so does the reason that the standard fix, a strip of 60,000 IU sachets, so often leaves people deficient again a year later.

Why the sun does not do the job here

Vitamin D synthesis needs UVB specifically, striking bare skin, at an angle steep enough to get through the atmosphere. Several things in ordinary Indian urban life independently break that chain, and most people are hit by more than one.

Melanin. Melanin is an effective natural sunscreen, which is its job. Deeply pigmented skin needs substantially longer exposure — commonly estimated at three to five times longer — to make the same amount of vitamin D as pale skin. Advice written for northern Europe does not transfer.

The hours are wrong. UVB is only strong enough between roughly 10am and 3pm. That is precisely the block of the day that anyone with an office job, a school-going child or a commute spends indoors. Early-morning and evening sun feels virtuous and produces very little.

Glass blocks UVB entirely. A sunny window seat, a car with the windows up, a glass-fronted office — none of it counts. This surprises people more than anything else on the list.

Coverage. Synthesis is roughly proportional to skin area exposed. Full-sleeved office clothing, or dress that covers arms and legs for cultural reasons, leaves the face and hands — a small fraction of body surface.

Air pollution. Particulate haze over major Indian cities measurably attenuates ground-level UVB. Delhi’s winter is not just unpleasant, it is optically thick.

Sunscreen, and the genuine trade-off it creates. Sunscreen does reduce synthesis. It also prevents photoageing and pigmentation, and skipping it to chase vitamin D is a poor bargain — supplements are cheap and hyperpigmentation is not easily reversed. Wear the sunscreen; fix the vitamin D another way. The same logic runs through the rest of a sensible routine, which I have covered in the skincare basics.

Add to that a national diet with almost no natural vitamin D in it — oily fish, egg yolk and liver are the meaningful food sources, and a large share of the population eats none of them — plus patchy fortification, and the deficiency rate stops being a paradox and starts being arithmetic.

Reading your report without panicking

The test is serum 25-hydroxy vitamin D. Indian labs usually report in ng/mL; some report in nmol/L, which is 2.5 times the ng/mL figure, and confusing the two is the single most common way people frighten themselves unnecessarily.

The thresholds in wide use, in ng/mL: below 20 is deficiency, 20 to 30 is insufficiency, and 30 and above is sufficiency. Indian expert consensus sits at that 30 mark. Below 10 to 12 is severe deficiency and is the range where bone disease becomes a real concern rather than a theoretical one.

What is not established is that higher is better without limit. There is no good evidence that pushing a healthy person from 35 to 70 buys anything, and a fair amount of expensive supplementation is aimed at exactly that.

The 60,000 IU sachet, and how it usually goes wrong

The near-universal Indian prescription is a 60,000 IU sachet weekly for eight weeks. As a correction protocol this is reasonable and it works — it reliably pulls a deficient level up into range.

The failure is what happens next, which is usually nothing at all. The course finishes, the sachets stop, nobody prescribes a maintenance dose, and the level drifts back down over the following months because every single cause listed above is still in place. A year later the same person tests deficient again, is handed the same eight sachets, and concludes that vitamin D supplements do not work. They worked. They were stopped.

Correction and maintenance are two different phases with two different doses, and the maintenance one is the phase that actually determines where you sit long term. What that dose should be for you depends on your starting level, your body weight, your sun exposure and what else you take — which is a conversation with your doctor, not a number to copy from an article.

Two things worth flagging on dosing:

• Very large single annual doses are not a shortcut. A well-known trial of a single 500,000 IU annual dose in older women found more falls and fractures in the treated group, not fewer. Bigger and less frequent is not the same as adequate and regular.
• Retest at the right moment. Roughly eight to twelve weeks after starting a correction course, and not sooner — testing a fortnight in produces a number that tells you nothing useful and often prompts the wrong next step.

D3, D2 and the cofactors people are sold

D3 versus D2. D3 (cholecalciferol) raises and maintains blood levels more effectively than D2 (ergocalciferol). Most D3 is derived from lanolin, which makes it unsuitable for strict vegans — lichen-derived D3 exists and is the option to look for, rather than settling for D2.

Magnesium. The enzymes that convert vitamin D into its active form are magnesium-dependent. Magnesium intake is commonly low, and there is a reasonable argument that poor response to supplementation sometimes reflects this. Worth knowing about; not worth panicking about.

Vitamin K2. Sold hard as an essential partner. The theory — directing calcium into bone rather than arteries — is plausible and the human outcome evidence is thin. If you take it, fine. It is not the reason your vitamin D is not working.

Calcium. Do not automatically stack calcium on top of high-dose vitamin D without someone checking whether you need it. Vitamin D increases calcium absorption; that is its mechanism. Adding a large calcium supplement to a correction course, in someone who did not need it, is the most common route to a raised calcium level. It is also worth knowing that calcium and iron both interfere with thyroid medication, which matters if you take levothyroxine.

What deficiency actually causes, and what it does not

Be clear-eyed here, because vitamin D has been credited with almost everything over the last fifteen years and most of it did not survive testing.

Well established: the bone and muscle effects. Severe deficiency causes rickets in children and osteomalacia in adults, with genuine bone pain and proximal muscle weakness. Correcting deficiency in deficient people improves that, and reduces fracture risk in older adults with low levels.

Not established: that supplementing people who are not deficient prevents cancer or cardiovascular disease. The large randomised trials, including a five-year trial of 2,000 IU daily in nearly 26,000 adults, did not find reductions in cancer incidence or major cardiovascular events. That is a genuinely useful result: it tells you to treat deficiency, and to stop chasing ever-higher numbers in the hope of a longevity benefit.

The fatigue question sits in between. Deficiency causes fatigue and muscle aches, and correcting it helps — but so many things cause the same symptoms that attributing them to a vitamin D of 24 and stopping there is how low ferritin, B12 deficiency and untreated thyroid disease go undetected for years. Fix the vitamin D and keep looking.

Toxicity is rare, and entirely self-inflicted

You cannot get vitamin D toxicity from sunlight; the skin regulates its own production. You can get it from supplements, and the cases that reach hospital are almost always people taking high-dose preparations daily rather than weekly, often for months, usually without testing, and frequently after a compounding error or a misread label.

It presents as hypercalcaemia: nausea, constipation, excessive thirst and urination, confusion, and eventually kidney damage. The relevant lesson is not that vitamin D is dangerous — it is that a 60,000 IU sachet is a weekly dose, and the difference between weekly and daily is a factor of seven.

Who should actually get tested

Routine testing of every healthy adult is not good use of money. Testing is worthwhile if you have bone or diffuse muscle pain, fractures, or a diagnosis of osteoporosis; persistent unexplained fatigue or proximal muscle weakness; very little sun exposure by occupation or dress; malabsorption — coeliac disease, inflammatory bowel disease, or after bariatric surgery; chronic kidney or liver disease; obesity, where vitamin D distributes into fat and blood levels run lower; darker skin at higher latitudes; pregnancy; or long-term steroids or anticonvulsants.

If you are getting bloods done anyway, it is a sensible addition — it belongs on the list of things a standard package tends to leave out, alongside ferritin and B12.

What to take away

• Melanin, indoor hours, glass, clothing coverage and urban haze each independently break vitamin D synthesis. Sunshine on the calendar is not sunshine on your skin
• Check the units. ng/mL and nmol/L differ by a factor of 2.5, and mixing them up causes needless alarm
• Below 20 ng/mL is deficient, 30 and above is sufficient. Higher than sufficient has not been shown to buy anything
• The eight-week sachet course corrects; it does not maintain. The missing maintenance dose is why people are deficient again a year later
• Retest at eight to twelve weeks, not at two
• Prefer D3, and lichen-derived D3 if you are vegan. Do not stack calcium onto a correction course without being told to
• Correcting deficiency helps bone and muscle. Supplementing beyond sufficiency has not prevented cancer or heart disease in trials
• Do not skip sunscreen to raise your vitamin D. That trade goes the wrong way

Before you act on any of this

I am a pharmacist and a nutritionist. I am not your doctor, and this article is general information rather than a dosing recommendation for you. Vitamin D dosing genuinely does need individualising, particularly if you have kidney disease, a history of kidney stones, sarcoidosis or another granulomatous condition, hyperparathyroidism, or a raised calcium level — in all of those, standard high-dose regimens can be actively unsafe. Doses in pregnancy and for infants are set separately. Do not start a high-dose course, and do not add calcium alongside one, without your doctor or pharmacist reviewing it against your reports. If you want the whole panel read together rather than one line at a time, that is what a one-time assessment covers.