Vitamin D deficiency

Vitamin D is less a vitamin than a hormone. Skin exposed to UVB converts a cholesterol precursor into vitamin D3; the liver turns that into 25-hydroxyvitamin D, the circulating storage form we measure; the kidney then activates it into the form that instructs the gut to absorb calcium and phosphate and regulates how bone is built and remodelled. Food contributes a small share for most people. Sunlight does the bulk of the work.

Which makes India's position genuinely paradoxical. A country with abundant year-round sunshine reports deficiency in a very large proportion of its population — across children, adults and older people, in cities and villages, among labourers working outdoors as well as office workers. Reported figures vary with the cut-off and the group studied, but are consistently high.

The reasons are specific, and they add up. Melanin is a natural sunscreen: deeper skin needs substantially longer UVB exposure to make the same amount of vitamin D as lighter skin. Sun avoidance is widespread and culturally reinforced, driven partly by a strong social preference for fairer skin, so shade, umbrellas and covered arms are the norm rather than the exception. Clothing that covers most of the body, including for religious reasons, leaves little skin exposed. Indoor work, long commutes and high-rise living remove daylight from the day entirely. Air pollution in North Indian cities attenuates UVB measurably. Latitude and season matter too — in the northern states, UVB is inadequate for vitamin D synthesis through the winter months. And until recently, India had almost no vitamin D fortification of its food supply, while diets are naturally low in the few good sources, which are fatty fish, egg yolk and liver.

Alongside this sits the point most often missed: calcium. Typical Indian calcium intake falls well below recommended levels, particularly in adults who take little dairy. Vitamin D deficiency on its own reduces calcium absorption; vitamin D deficiency combined with low calcium intake is what produces osteomalacia — soft, poorly mineralised bone that aches. Treating one and ignoring the other leaves the job half done.

Two more factors are worth knowing. Body size matters, because vitamin D is fat-soluble and is sequestered in adipose tissue, so people carrying more fat need more to reach the same blood level. And in older adults, skin makes vitamin D less efficiently while falls and fracture risk rise, which is where treatment has its clearest benefit.

Now the part that separates honest information from marketing. There are two very different claims made about vitamin D. The first — that deficiency causes real bone disease, rickets in children, osteomalacia in adults, and secondary hyperparathyroidism — is well established, common in India, and worth treating. The second is the long list of claimed benefits for immunity, cancer, cardiovascular disease, depression and COVID. Those associations appeared in observational studies, but large randomised trials of supplementation have been mostly disappointing. Low vitamin D often marks poor health rather than causing it. Treating deficiency is worthwhile; expecting it to prevent unrelated illness is not supported.

ⓘThis information is educational and not a diagnosis.

Most vitamin D deficiency produces no symptoms at all, and is found because a health package included the test. Where symptoms do occur, they are unglamorous and easily attributed to age, work or stress.

Bone pain is the characteristic one — a deep, dull ache rather than a sharp pain, felt in the shins, ribs, hips, pelvis and lower back, worse on pressure and often worse at night. People describe it as coming from inside the bone, which is exactly where it originates, in poorly mineralised tissue.

Proximal muscle weakness is the other classic feature and the more useful clue, because it is specific. The muscles around the hips and shoulders are affected, so the difficulty is in rising from a low chair or from the floor, climbing stairs, or lifting arms overhead — while grip strength stays normal. A waddling gait can develop. This weakness improves substantially with repletion, which makes it worth recognising rather than accepting.

In children, deficiency presents as rickets: delayed walking, bowing of the legs, widened wrists, a prominent forehead, and slow growth. In older adults, it contributes to falls, and a fracture after a minor fall may be the first indication.

Fatigue and low mood are frequently attributed to low vitamin D. They are common in deficiency and also common in people with normal levels, so they are a reason to test rather than a reason to conclude.

The features listed below sit in a different category, including the symptoms of raised blood calcium after high-dose supplementation, and they warrant prompt review.

Serum 25-hydroxyvitamin D is the right test. The 1,25-dihydroxy form is sometimes ordered by mistake; it is regulated tightly and can read normal in clear deficiency, so it answers a different question altogether.

The thresholds in wide use are: deficiency below 20 ng/mL, insufficiency 20-30 ng/mL, and sufficiency above 30 ng/mL. These figures are contested rather than settled. Several expert bodies hold that 20 ng/mL is adequate for bone health at a population level, and that the higher target has driven a great deal of unnecessary supplementation. Indian laboratories report in ng/mL; where a source quotes nmol/L, dividing by 2.5 converts it.

Routine screening of people without symptoms is not recommended by most guidelines, despite the test appearing in nearly every Indian health package. Testing earns its place where there is bone pain, proximal weakness, a low-trauma fracture, malabsorption such as coeliac disease, chronic kidney or liver disease, in older adults at risk of falls, or where a treatment decision genuinely turns on the result.

Where deficiency is causing bone disease, the vitamin D level is not the whole picture. Serum calcium and phosphate tend to fall or sit at the lower edge. Alkaline phosphatase rises, and a raised ALP alongside bone pain is a genuinely useful clue. ALP is also one of the enzymes on a standard liver function test, where a mildly raised value with normal transaminases is sometimes chased as a liver problem when its source is bone. Parathyroid hormone rises in prolonged deficiency as the body defends its calcium, and a raised PTH indicates the deficiency is having a real effect rather than simply reading low.

Kidney function is relevant both because the kidney performs the activation step and because it is the organ that suffers when blood calcium is pushed too high by over-supplementation.

Repeat testing has its own timing. A level checked a day or two after a high-dose sachet reflects the sachet rather than the person. Where a recheck is useful, it is usually done around eight to twelve weeks after starting treatment, which is long enough for the stored form to settle at a new steady value. Rechecking every few months in someone who feels well adds cost without adding clarity, and is a large part of why so many Indian families hold a folder of vitamin D reports and no clear plan.

How repletion is commonly done in India. The familiar approach is a weekly 60,000 IU cholecalciferol sachet for a defined number of weeks, followed by a lower maintenance approach. That is what is commonly prescribed; the number of weeks, the maintenance plan and whether treatment suits you at all are decisions for your doctor, made against your level, your symptoms and your kidney function. Cholecalciferol (D3) raises and holds blood levels more effectively than ergocalciferol (D2) and is the standard choice in India. Because vitamin D is fat-soluble, taking it with a meal containing some fat improves absorption noticeably — a common and easily fixed reason for a level that refuses to rise.

On over-supplementation. This deserves real emphasis. Vitamin D is stored in fat and accumulates. High-dose sachets bought over the counter and repeated for months, or injections given at intervals nobody is tracking, are now a recognised and rising cause of hypervitaminosis D in India. The result is high blood calcium, which presents as excessive thirst, frequent urination, nausea, constipation, confusion and, over time, kidney damage and stones. This is entirely avoidable with a defined course and a follow-up level. Vitamin D is not a supplement where more is better.

Calcium alongside. Vitamin D governs absorption; calcium is what gets absorbed. Realistic Indian sources include milk, curd, paneer, ragi, sesame and til, rajgira and amaranth, drumstick leaves, and small fish eaten with bones. Lactose intolerance is common in parts of India, particularly in the south and east, so curd, paneer and non-dairy sources are often more workable than milk. Vegetarian diets carry almost no vitamin D themselves, which is part of the broader pattern of micronutrient deficiencies clustering together — vitamin D, B12 and iron frequently appear on the same report.

Sunlight, sensibly. Mid-morning or mid-afternoon exposure of the arms, legs and back for a period appropriate to your skin tone, several times a week, is the natural route. Deeper skin needs longer. This has to be balanced against sun protection, and for many people supplementation is more practical than restructuring the day around it.

Movement. Weight-bearing and resistance exercise builds bone and muscle in a way no supplement replicates, and it addresses the falls risk that makes deficiency dangerous in later life. At menopause, when bone loss accelerates, this combination of adequate vitamin D, adequate calcium and loading the skeleton matters more than at any earlier stage.

Vitamin D is the number most Indians have seen on a report, and the one most likely to have been acted on without much thought — a sachet started, or a low value dismissed entirely.

If you would like to understand how to read your own reports properly — what the cut-offs mean, why ALP and calcium sit beside the vitamin D level, and which findings genuinely warrant follow-up — the Learning Session below works through it in a small group, with time for questions.

If you have bone pain, difficulty rising from a chair, or have been taking high-dose supplements without a review, that is a conversation for a consultation rather than an article.