Why vitamin D deficiency is so common in a country this sunny

India gets a great deal of sunshine and a great deal of vitamin D deficiency. Surveys repeatedly report deficiency in a majority of the people tested, including in sunny cities, including in people who work outdoors.

That looks like a contradiction. It is not. There are six separate reasons, and they stack.

And there is a seventh thing going on that nobody says out loud: a meaningful part of that alarming prevalence figure is an argument about where to draw the line, not about anyone’s health.

We sell vitamin D drops. This article explains the real mechanism, and also where the deficiency statistics are softer than they sound.

General information, not medical advice. And one warning that belongs at the top: vitamin D toxicity is a real and growing problem in India, caused by high-dose sachets and injections taken wrongly. It is at the end of this article and it matters.

Reason one: UVB needs the sun overhead

This is the one that resolves most of the paradox, and almost nobody knows it.

Vitamin D synthesis in skin is driven by UVB radiation, in a narrow wavelength band.

And UVB behaves very differently from UVA and from visible light. It is strongly absorbed by the atmosphere.

So when the sun is low in the sky, the light travels a long slanting path through the atmosphere, and the UVB is largely filtered out before it reaches you.

Practically:

UVB reaches the ground meaningfully only when the sun is high, roughly between 10 am and 3 pm.

Early morning sun makes almost no vitamin D. Evening sun makes almost none.

And this is exactly inverted from Indian habit. The advice is to take morning sun. The walk is at 6 am. The terrace sitting is at sunset. People deliberately avoid 11 am to 3 pm, because it is hot.

So a person can be out in the sun daily, for years, and synthesise very little vitamin D, because they are out in the hours when the sun does not make it.

This single fact explains more of the Indian picture than everything else combined.

Reason two: melanin

Melanin absorbs UV. That is its function, it is photoprotective, and it is why darker skin burns less and ages better.

And the same protection reduces vitamin D synthesis.

Studies comparing skin types consistently find that more pigmented skin requires substantially longer UVB exposure to produce the same amount of vitamin D, multiples of the time, not a small increment.

So the sun exposure rules written for European skin do not transfer. “Fifteen minutes of sun” is a figure derived from pale skin at a high latitude. For Indian skin types it understates the requirement considerably.

And this is not a defect. It is an adaptation to high UV environments that becomes a disadvantage when behaviour changes, when people move indoors, work night shifts, or cover up.

Reason three: behaviour and cities

Indoor work. The shift from field labour to offices, factories, call centres and shops is the largest behavioural change in Indian vitamin D status.

Glass. Window glass blocks UVB almost entirely. Sitting by a sunny window, or driving in a car, produces no vitamin D. People find this hard to believe, and it is straightforwardly true.

Clothing that covers most of the skin, for cultural, religious, occupational or modesty reasons. Synthesis depends on exposed surface area, so a face and hands are a small fraction of what arms, legs and back would give.

Deliberate sun avoidance for skin tone. This deserves naming: a large industry sells sun avoidance and skin lightening, and the fear of tanning keeps people out of the hours when UVB is available. The social preference for lighter skin has a measurable nutritional consequence.

High-rise living, with less terrace and courtyard time.

And sunscreen, which works as designed, though in practice most people apply too little for it to be the main factor.

Reason four: air pollution

And there is actual Indian evidence for this one.

Particulate air pollution attenuates UVB reaching ground level. Studies comparing children in heavily polluted and less polluted parts of Indian cities have found lower vitamin D levels in the polluted areas.

So in Delhi, Kanpur or Lucknow in winter, the combination of a low sun angle and heavy particulate haze can mean very little usable UVB for weeks.

North Indian winter is, in vitamin D terms, closer to a northern European winter than the latitude suggests.

Reason five: the diet has almost none

This is where India differs sharply from the West, and it is a policy difference rather than a cultural one.

Natural dietary vitamin D is concentrated in a very short list: oily fish (salmon, mackerel, sardines), cod liver oil, egg yolk, liver, and some mushrooms exposed to UV.

Which means:

A lacto-vegetarian Indian diet contains essentially no vitamin D. Not a little, effectively none. Milk, curd, paneer, dal, roti, rice, vegetables: nothing meaningful.

And here is the policy point. In the United States and Canada, milk has been fortified with vitamin D for decades. That single public health measure is why their dietary intake is not zero.

India’s milk is largely unfortified. Fortification is permitted and increasing, FSSAI has a fortification framework and a “+F” logo for fortified foods, and fortified milk and edible oil are available, but coverage is partial and most households are not getting it.

So the Indian population has the sun exposure pattern of an indoor northern population, with the dietary vitamin D of a country that fortifies nothing.

That combination, not the latitude, is the story.

Reason six: body fat and other biology

Vitamin D is fat-soluble, and in obesity it distributes into adipose tissue, lowering circulating levels for the same intake. Obesity is rising rapidly in urban India.

Older age, skin synthesis declines with age.

Kidney and liver disease, vitamin D requires hydroxylation in both organs to become active.

Malabsorption, coeliac disease, inflammatory bowel disease, bariatric surgery.

And certain drugs, some anti-epileptics, rifampicin, glucocorticoids, increase vitamin D breakdown.

Exclusively breastfed infants, because breast milk is low in vitamin D unless the mother is replete. This is why infant supplementation is recommended, and we have written separately about paediatric dosing.

And the seventh thing: the threshold argument

This section is the one that makes us unusual among people selling vitamin D, so we will be careful and plain.

The “70–90% of Indians are deficient” figures you see depend heavily on where the cutoff is drawn.

The measurement is serum 25-hydroxyvitamin D, in ng/mL.

And there are two influential positions:

One body of expert opinion treats below 20 ng/mL as deficient and 20–30 as insufficient, with above 30 as the target.

Another, including the Institute of Medicine’s assessment, which informed the dietary reference intakes, concluded that 20 ng/mL is adequate for bone health in most of the population.

That is a difference of ten units, and it moves the prevalence figure enormously. A survey using 30 ng/mL will find most Indians deficient. The same survey using 20 ng/mL will find far fewer.

Which means two things can both be true:

Genuine, clinically important vitamin D deficiency exists in India in large numbers, rickets in children and osteomalacia in adults are real, present, and sometimes severe.

And the dramatic prevalence headlines are partly a function of a chosen threshold, and they are used commercially.

We think honesty requires saying both. The people selling vitamin D, us included, benefit from the higher threshold.

What vitamin D actually does, and what it does not

Where the evidence is solid:

Calcium absorption from the gut. This is its core, undisputed job. Without adequate vitamin D, dietary calcium is poorly absorbed, which is why calcium and vitamin D are formulated together.

Bone mineralisation. Deficiency causes rickets in children, bowed legs, delayed walking, wrist and rib changes, and osteomalacia in adults, with bone pain and muscle weakness. These are the diseases vitamin D was discovered through, and they are not historical in India.

Muscle function, and fall reduction in deficient older adults.

Where the evidence is much weaker than the marketing:

And this needs saying, because vitamin D spent a decade being sold as a cure for everything.

Cancer prevention, cardiovascular disease prevention, and diabetes prevention, large randomised trials of vitamin D supplementation in largely replete populations have been substantially negative on these outcomes.

Immunity, some signal for respiratory infections in deficient people, and far less impressive than the claims made during the pandemic.

Depression, autoimmune disease, weight loss, “energy”, not established.

And the honest interpretation of that pattern: correcting a deficiency helps the deficient person. Supplementing someone who is already replete, in the hope of preventing unrelated diseases, has mostly not worked when tested properly.

Low vitamin D is often a marker of being indoors, unwell or inactive, rather than the cause of those things. That confounding explains a great deal of the observational literature that drove the enthusiasm.

Toxicity, the Indian problem nobody expected

And this is the part of the article we would most want someone to read.

Vitamin D is fat-soluble and stored. It can be overdosed, and in India it is being overdosed.

Why here specifically:

The 60,000 IU sachet is the standard Indian prescription, taken weekly.

And it gets taken daily. Either through misunderstanding, or because the instruction was unclear, or because someone decided more would be faster. 60,000 IU daily for weeks is a toxic dose.

High-dose injections are given casually.

And it is available without real oversight, with repeat courses taken without retesting.

What toxicity does: hypercalcaemia, too much calcium in the blood.

Symptoms: nausea, vomiting, poor appetite, constipation, excessive thirst, frequent urination, weakness, confusion, and in severe cases kidney damage and calcium deposition in tissues.

Case series of vitamin D toxicity have been reported from Indian centres, and the pattern is consistent: high-dose preparations taken more often than intended.

So the practical rules:

Read the frequency on the sachet. Weekly means weekly.

Do not take repeat high-dose courses without retesting.

Do not take high-dose vitamin D without knowing your level.

And be careful about stacking, a sachet plus a multivitamin plus a calcium-and-D tablet plus an injection adds up, and nobody is totalling it.

This is the rare supplement where “a bit more to be safe” is a genuinely bad idea.

So what should someone actually do

Get tested before taking high doses. Serum 25-hydroxyvitamin D. And know which threshold your lab is using when it prints “deficient”.

Sun, used correctly, if you can: between about 11 am and 2 pm, arms and legs exposed, no sunscreen on those areas for that period, for a duration suited to your skin type, longer for more pigmented skin. Short of burning, always. And this has to be weighed against skin cancer and photoageing risk, which is why many dermatologists prefer supplementation to deliberate sun exposure.

Supplement if deficient, at a dose and frequency a doctor sets, and retest rather than repeating indefinitely.

Maintenance doses are modest, typically in the hundreds to ~2000 IU daily range for adults, depending on the guidance followed. The 60,000 IU sachet is a correction dose, not a maintenance dose.

Take it with a meal containing fat. It is fat-soluble, and this genuinely improves absorption.

And get enough calcium, because vitamin D’s main job is absorbing it, and correcting D without adequate calcium intake does not fix a bone problem.

What we will and will not say

Sayable: the authorised nutrient-function claims for vitamin D, where present in a significant quantified amount, contribution to normal absorption and utilisation of calcium and phosphorus, normal blood calcium levels, maintenance of normal bones, teeth and muscle function, normal functioning of the immune system, and a role in cell division, in the permitted wording. And for children’s products, the claim relating to normal bone growth and development.

Not sayable: prevents cancer, prevents heart disease, prevents diabetes, treats depression, cures fatigue, “boosts immunity” in the loose sense, aids weight loss.

And two refusals of ours:

We will not quote the 70–90% deficiency statistic as a selling line, because it is threshold-dependent and we benefit from the higher threshold.

And we will not sell 60,000 IU sachets as a general wellness product. It is a therapeutic correction dose and it belongs in a prescription context, because the toxicity we are seeing in India comes from exactly that dose being treated casually.

And the most honest summary:

UVB only reaches you when the sun is high, which is the window Indians avoid. Melanin needs several times longer. Glass blocks it, pollution attenuates it, and the vegetarian Indian diet contains essentially none, in a country that, unlike North America, does not fortify its milk.

That is why a sunny country is deficient.

And the prevalence headlines are partly a threshold argument, the big disease-prevention claims largely failed when tested, and the 60,000 IU sachet is now causing toxicity.

Correcting a real deficiency is worth doing. Everything beyond that has been oversold, by an industry we are part of.

When to see a doctor

Get tested, and seen, if you have:

• bone pain, especially in the pelvis, hips, ribs or shins
• difficulty rising from a chair or climbing stairs, proximal muscle weakness
• a waddling gait
• frequent fractures, or a fracture from a minor fall
• in a child: bowed legs, delayed walking, a swollen wrist or forehead, delayed teeth, or frequent fractures, this needs a paediatrician, not a sachet

Ask about testing if you: work indoors; cover most of your skin; have obesity; have kidney or liver disease; have coeliac disease, inflammatory bowel disease or bariatric surgery; take anti-epileptics, rifampicin or long-term steroids; are pregnant or breastfeeding; or are elderly or housebound.

Stop and get urgent advice if, while taking vitamin D, you develop: nausea and vomiting, loss of appetite, constipation, unusual thirst, frequent urination, marked weakness, or confusion, these are symptoms of high blood calcium. Say what dose you took and how often.

And check this now if it applies: if you were given a 60,000 IU sachet and have been taking it daily rather than weekly, stop and speak to a doctor.

The short version

1. UVB is strongly absorbed by the atmosphere, so it needs the sun high overhead
2. Meaningful synthesis happens roughly 10 am to 3 pm
3. Early morning and evening sun make almost none
4. Which is exactly the Indian habit, the walk is at 6 am
5. So someone can be outdoors daily for years and synthesise very little
6. Melanin absorbs UV, so pigmented skin needs multiples of the exposure time
7. “Fifteen minutes of sun” is a figure derived from pale skin at high latitude
8. Window glass blocks UVB almost completely, a sunny window gives nothing
9. Covered clothing reduces the exposed surface area that drives synthesis
10. Deliberate sun avoidance for skin tone has a measurable nutritional cost
11. Particulate pollution attenuates ground-level UVB, with Indian evidence
12. North Indian winter resembles a northern European one in vitamin D terms
13. Natural dietary vitamin D is in oily fish, liver, egg yolk and UV mushrooms
14. A lacto-vegetarian Indian diet contains effectively none
15. US and Canadian milk has been fortified for decades; Indian milk largely is not
16. FSSAI permits fortification with a “+F” logo, and coverage is partial
17. So India has indoor sun habits and an unfortified diet
18. Obesity sequesters vitamin D in fat, lowering circulating levels
19. Some anti-epileptics, rifampicin and steroids speed its breakdown
20. Breast milk is low in vitamin D unless the mother is replete
21. The 70–90% deficiency figure depends on the chosen cutoff
22. One view calls below 20 ng/mL deficient and targets above 30
23. The Institute of Medicine assessment concluded 20 is adequate for most
24. Ten units of threshold moves the prevalence figure enormously
25. Real deficiency is common AND the headline figures are threshold-dependent
26. Sellers of vitamin D, including us, benefit from the higher threshold
27. Its core undisputed job is calcium absorption from the gut
28. Rickets and osteomalacia are present in India, not historical
29. Large trials of supplementation for cancer, heart disease and diabetes were substantially negative
30. Correcting deficiency helps; supplementing the replete mostly has not
31. Low vitamin D is often a marker of being indoors or unwell, not the cause
32. Vitamin D toxicity is a real and growing Indian problem
33. The 60,000 IU weekly sachet gets taken daily, that is a toxic dose
34. Toxicity causes hypercalcaemia: nausea, thirst, confusion, kidney damage
35. Watch for stacking, sachet plus multivitamin plus calcium-D plus injection
36. Use the sun between 11 am and 2 pm if at all, and never to burning
37. Take it with a meal containing fat, it is fat-soluble
38. And get enough calcium, since absorbing it is what vitamin D is for

Our formulations: Vitamin D3 Drops, Calcium & D3 Capsule. Related reading: vitamin D drops vs capsule vs weekly sachet, बच्चों के लिए विटामिन D कितनी मात्रा, vegan D3 from lichen, विटामिन D की कमी के लक्षण, and calcium, D3 and K2 together.