Sapiens · Vitamins

Vitamin D Deficiency: Symptoms, Causes, and Treatment

Vitamin D deficiency means your blood 25-hydroxyvitamin D is below 20 ng/mL. Below 10 ng/mL is severe, 20 to 30 is insufficiency, and 30 or above is sufficient. Most people sitting at those levels feel nothing at all.

In India, surveys put 60 to 80% of adults below that line — though the most-quoted Indian figure, 79%, comes from a study of hospital doctors and nurses, whose working lives are spent indoors, so read it as a high-risk occupational group rather than the country.² A number that large should make you suspicious of the line itself, which is why the more useful question is not whether you are under it but whether being under it is causing you a problem. This guide covers what the level means, who needs testing, how a real deficiency is corrected, and who is being over-medicalized.

What is vitamin D deficiency? Copy link

Vitamin D deficiency means your blood level of 25-hydroxyvitamin D — the form doctors measure — is too low for your body’s needs. The widely used thresholds, including the Indian endocrinology consensus, define deficiency as below 20 ng/mL, severe deficiency as below 10 ng/mL, and insufficiency as 20–30 ng/mL, with sufficiency at 30 ng/mL or above.¹

Is 18 ng/mL actually a problem? Copy link

If you have no symptoms, probably not. Picture a 34-year-old in an air-conditioned Bengaluru office who tests at 18 because a full-body package included it. She feels fine, eats normally, has no bone pain and no fracture history. Nothing about that number, on its own, describes a person who is unwell. A reading of 18 sits under the 20 ng/mL line and gets reported as “deficient,” but that line was drawn on Western populations and Indian data suggest it is set too high here. Studies tracking parathyroid hormone and calcium in Indians find that levels above roughly 12 ng/mL are generally enough to keep blood calcium normal and stop the parathyroid gland from compensating.⁴ Those two things are what a vitamin D level exists to protect.

The large trials point the same way. VITAL supplemented people who were not deficient and found no reduction in most non-bone disease.⁵ So the headline that most of India is deficient is substantially an artifact of where the line sits.⁴ The Endocrine Society reached the same practical conclusion from the other direction in 2024, recommending against routine testing of healthy adults and declining to set a sufficiency threshold at all.⁹ Genuine symptomatic deficiency is real and worth correcting, and that is what a 25(OH)D test is for. A quiet 18 in someone who feels well is a different animal, and treating it as an emergency is how healthy people end up on years of supplements they never needed.

So is 32 ng/mL fine?

Yes, for most people. Thirty-two clears the conventional sufficiency line of 30 and sits below the 40 to 60 band the Indian consensus aims for.¹ That band is a target for treatment, not a threshold that makes everything under it abnormal. The 2024 Endocrine Society guideline went further and declined to name a sufficiency number at all, on the grounds that no level has been shown to predict better outcomes.⁹ If you feel well and have no risk factors, 32 needs nothing.

What does vitamin D actually do in the body? Copy link

Vitamin D controls how your body absorbs calcium. Without enough, your gut can’t absorb dietary calcium properly, which over time weakens bones, causing rickets in children and soft, painful bones (osteomalacia) in adults. Those two are the classic vitamin D deficiency diseases. Nothing in that chain is scientifically contested; the arguments all start further downstream.

Does low vitamin D cause symptoms? Copy link

The signs are easy to miss: most people with a “low” vitamin D level have no symptoms at all. When symptoms do occur, they tend to be non-specific and overlap with many other conditions, so testing beats guessing. Reported symptoms include:

• Bone pain and tenderness, especially in the legs, hips, or lower back
• Muscle weakness, aches, or cramps
• Fatigue and low energy
• Frequent or prolonged illness (vitamin D supports immune function)
• Low mood, in some people
• In children: delayed growth, bowing of the legs, or rickets in severe cases

Because these are vague and common, they don’t confirm deficiency on their own, but if you have them alongside risk factors, that’s a strong reason to test instead of self-diagnosing.

Why is vitamin D deficiency so common in India? Copy link

India sits in a sunny, tropical zone, yet reports some of the world’s highest deficiency rates. A multi-city study of over 2,000 Indian health professionals found 79% deficient, with an average level around 14 ng/mL and no real difference between north and south.² A recent meta-analysis of Indian children and adolescents found about two-thirds (66%) deficient.³

The reasons behind the paradox are specific and worth knowing: indoor lifestyles mean little skin actually meets the sun; higher melanin protects against sunburn but makes vitamin D more slowly; covered clothing and urban air pollution cut UVB exposure further; and diet contributes little, since the richest natural source is oily fish, which most Indian vegetarian diets exclude.

A subtler Indian factor gets missed in the sunshine argument. In a study of urban and rural south Indians, rural adults — who spend far more of the day outdoors — still showed widespread deficiency, alongside dietary calcium well below Indian recommended intakes and a diet high in phytates, the compounds in cereals and legumes that bind calcium and block its absorption.⁶ Low dietary calcium makes the body use up vitamin D faster, so a calcium-poor plate drags the level down even where sunlight is plentiful. Correcting vitamin D without correcting calcium treats half the problem.

How much sunlight do you actually need? Copy link

“Get more sun” is not advice anyone can act on. Three things decide how much vitamin D you make: how much skin is bare, how long it stays exposed, and at what hour. UVB is strong enough to drive synthesis only around the middle of the day; the soft early-morning and evening light that feels pleasant does very little. Bare forearms and lower legs for 20 to 30 minutes, several times a week, is the usual starting point in Indian conditions — and darker skin needs longer, because the melanin that protects against burning filters the same UVB that makes the vitamin.

Then there is everything that quietly cancels it out. Sunscreen, window glass, and covered clothing all block UVB, so a commute behind a windscreen and a day beside an office window contribute nothing at all. Urban haze scatters what is left before it reaches skin. In a 2025 study of young urban Indian women, three-quarters of those found deficient were getting under 15 minutes of sun a day.⁷ That was a cross-sectional study of young urban women, so read it as a snapshot of that group. For an indoor city life, sunlight alone rarely closes the gap.

Which foods actually contain vitamin D? Copy link

Fewer than most lists promise. No fruit contains vitamin D. No vegetable does either. Oranges, bananas, and spinach earn their place on a plate for other reasons — calcium, magnesium, fiber — but none of them supplies the vitamin itself.

The real sources are a short list: oily fish, egg yolk, and mushrooms that have been exposed to ultraviolet light. Mushrooms are fungi rather than vegetables, and they are the one entry from the plant aisle worth knowing about. Since UVB does not pass through window glass, a packet left on a sunny windowsill achieves little; direct outdoor light is what counts. Mushrooms also produce D2 rather than the D3 found in animal sources and most supplements; at the higher doses used to correct a deficiency, D3 raises blood levels more reliably.⁸

That leaves fortified foods — milk, some plant milks, and cereals, where the vitamin is added during processing rather than naturally present — as the most dependable dietary route on a vegetarian diet. Even so, food alone rarely corrects an established deficiency, so treatment uses a supplement.

What causes vitamin D deficiency? Copy link

Beyond the India-specific factors, the common causes are:

• Too little sunlight — the single biggest cause for most people.
• Darker skin and older age, both of which reduce how much the skin produces.
• An indoor life — office workers, the elderly, and the housebound.
• Obesity, where vitamin D is sequestered in body fat.
• Malabsorption from celiac disease, IBD, or bariatric surgery.
• Exclusive breastfeeding without supplementation in infants.

How is vitamin D deficiency treated? Copy link

Treatment is straightforward and effective when it’s actually needed. For diagnosed deficiency, doctors typically prescribe a course of vitamin D3 (cholecalciferol) — usually a higher dose for several weeks to rebuild stores, followed by a lower maintenance dose. A few practical points on treatment:

• Sunlight and diet help, but often aren’t enough to correct an established deficiency on their own, so a supplement usually does the correcting.
• More isn’t better. Careless high “loading” doses, or long-term self-dosing of mega-amounts, can cause vitamin D toxicity (high calcium), so dosing should follow medical advice, not a social-media trend.
• It comes in several formats. Tablets, sachets, oral drops and solutions, and injections in specific situations — which format suits you is a clinical decision, not a shelf-browsing one.
• Take it with a meal containing some fat. Vitamin D is fat-soluble, so absorption from a supplement is better with food than on an empty stomach.
• Mind the calcium alongside it. Indian diets are frequently low in calcium, and topping up vitamin D without enough dietary calcium leaves the bone side of the problem only partly addressed.⁶
• Recheck, don’t just keep dosing. The point is to correct the level and confirm it, not to take high doses indefinitely.

What dose does the Indian consensus recommend?

The 2025 Indian expert consensus publishes a specific adult schedule, and it is worth knowing so you can tell whether what you have been handed is standard practice.¹ For diagnosed deficiency, below 20 ng/mL, it recommends cholecalciferol 60,000 IU once a week for 12 weeks. For insufficiency, 20 to 30 ng/mL, the same weekly dose for 8 weeks. Once the level is sufficient, both step down to 60,000 IU once a month to hold it there. The level it aims for is 40 to 60 ng/mL. Adults over 65 are handled differently, and neonates, children, pregnancy, and several medical conditions each carry their own schedules in the same document.

Two things qualify those numbers. They are population guidance, not a prescription: body weight, absorption, kidney and liver function, and other medication all shift what any individual needs, so the dose is your doctor’s to set. And correction is meant to end. The consensus moves you down to maintenance once you are sufficient instead of leaving you on weekly high doses indefinitely, which is the pattern that leads to toxicity.

This schedule is for adults under 65. Adults 65 and over, neonates, children, pregnancy, and specific conditions carry separate schedules in the same consensus, and dosing is your doctor’s to set.¹

How long does it take to correct?

Plan on the loading phase running 8 to 12 weeks, and on retesting at the end of it instead of assuming it worked.¹ Where symptoms did come from the deficiency, bone and muscle aches tend to ease over several weeks, not days. If you feel no different once the level is corrected, that is informative in its own right: it suggests vitamin D was not the cause of the symptom, and the search should carry on instead of stopping at a normal number.

How much vitamin D do you need a day? Copy link

For maintenance rather than correction, the Indian reference intake is 600 IU a day for adults, set by the ICMR-NIN expert group in 2020, which adopted the international figure while stressing that outdoor activity is how a tropical country is supposed to meet it.¹¹ US guidance matches at 600 IU, rising to 800 IU from age 71.⁸ The 2024 Endocrine Society guideline suggests healthy adults under 75 have no reason to go beyond that, and no reason to test in order to decide.⁹ That is a maintenance figure. It is not the same as the loading schedule above, which exists to refill depleted stores and then stops.

How much vitamin D is too much? Copy link

The page has said several times that over-supplementing can do harm, so here are the numbers. The tolerable upper intake level for adults is 4,000 IU a day taken chronically.⁸ Indian paediatric guidance defines outright toxicity as a 25(OH)D above 100 ng/mL together with a high blood or urine calcium.¹⁰ Between those two points is a wide margin, so a supervised 60,000 IU weekly course is not where the danger lies. The risk is staying on a loading dose for months because nobody retested, and the damage runs through calcium: hypercalcemia, kidney stones, and in severe cases soft-tissue calcification and kidney injury.⁸

Should you get tested? Copy link

Testing makes the most sense if you have symptoms (bone pain, muscle weakness, persistent fatigue), risk factors (little sun exposure, darker skin, older age, obesity, a vegetarian diet, pregnancy), or a related condition (osteoporosis, malabsorption). Routine mass-screening of healthy, symptom-free people isn’t clearly supported by evidence, which is why a quick vitamin D test, interpreted with your symptoms and risk factors, beats either ignoring it or blindly supplementing.

If you have symptoms or risk factors, test before you treat. Your 25(OH)D read by a doctor, alongside calcium and the rest of your picture.

When should you see a doctor about low vitamin D? Copy link

See a doctor if you have ongoing bone or muscle pain, unexplained fatigue (which also overlaps with B12 deficiency and anemia), frequent infections, or risk factors for deficiency — or if a test comes back low and you’re unsure how to interpret or treat it. Self-prescribing high-dose vitamin D without testing or guidance can do more harm than good.

This article is for general education and is not a substitute for personal medical advice. Vitamin D dosing should be set by a doctor, as too much can be harmful. Discuss testing and treatment with a clinician who knows your symptoms and risk factors. Written by Dr Tarun Reddy, MBBS.