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Low vitamin D is one of the most common results on Indian blood reports, which surprises people in a country with this much sun. Most find out by accident, from a full-body package booked for some other reason, because the symptoms are vague enough to blame on the commute, getting older or a bad mattress.
Plenty of people with a low level feel nothing at all. When it does cause trouble, the usual complaints are aching bones, a dull ache in the lower back or thighs, weak muscles and tiredness. A long, severe deficiency softens the bones. All of this overlaps with a dozen other problems. The only reliable way to know is a blood test for 25-hydroxyvitamin D, which most labs here print as "Vitamin D, 25-OH".
What are the symptoms of vitamin D deficiency?
Often there aren't any you would notice. Vitamin D helps the gut absorb calcium and keeps bones mineralised, and the body can manage on a low supply for months or years before anything hurts. Michael Holick, the Boston endocrinologist whose 2007 review in the New England Journal of Medicine is still widely cited, calls the deficiency common and often silent.
When it does make itself felt, it's mostly in bones and muscles. People describe a deep, dull ache in the lower back, hips, thighs or shins, legs that feel heavy by evening, and a tiredness that a full night's sleep doesn't shift. A severe deficiency that runs for years softens the bones. In adults that's called osteomalacia, and a doctor pressing firmly on the shin or breastbone may find it tender. If those aches have been around for weeks, describe them to your doctor in those words, because "body pain" on its own tends to get a painkiller.
Sources: [1]
Why is it so common in a sunny country?
Very little of that sun ever lands on skin. Most office workers in Pune or Noida leave home at eight in a car or a packed bus, sit under tube lights until seven, and get back after dark. In a hot climate we look for shade when we do go out. Long sleeves, a dupatta or a full salwar cover most of the body, and on a smoggy winter day the haze filters out a good share of the UVB that would have reached it.
Skin colour adds to this. Melanin is a natural sunscreen, so brown skin needs longer in the sun to make as much vitamin D as pale skin does. A 2018 review of Indian studies in the Journal of Family Medicine and Primary Care found deficiency in every age group, region and income bracket it looked at. Its authors also blame a largely vegetarian diet and the fact that few foods here are fortified.
Which signs are easiest to miss?
Muscle weakness, because it comes on so slowly that you adjust to it. The lift in your building is out and the three floors leave your thighs burning. You start putting a hand on your knee to get up after sitting cross-legged at a puja, or to climb out of a low sofa. The walk to the vegetable market leaves your legs aching in a way it didn't two years ago.
Vitamin D acts on muscle directly as well as through bone. Jenny Gunton and Christian Girgis, who reviewed that research in 2018, describe weakness and more falls in people who are deficient, especially older adults. Most of us put this down to age or not exercising, and often that's right. If your parents are in their sixties and have started holding the railing on every step, though, a vitamin D test is an easy thing to rule out.
Sources: [5]
Do hair fall, low mood and tiredness point to low vitamin D?
They might. The research is shakier than the forwards on the family WhatsApp group suggest, though. Observational studies find low vitamin D more often in people who are tired or low, but people who feel unwell tend to stay in, and staying in pulls vitamin D down. So the low level could be a result of feeling bad as easily as the cause of it, and trials that gave vitamin D to tired or low people have had mixed results.
Hair fall is harder still to pin on it. A doctor in India will usually think of low iron first, then the thyroid, PCOS, and the shedding that can follow a bad fever. If clumps in the comb are what sent you looking, ask for ferritin and TSH in the same blood sample as vitamin D, so all three can be read side by side.
Sources: [1]
Who is most likely to be deficient?
The Endocrine Society's guideline lists the people it thinks should be tested. They are people with darker skin, older adults, anyone who gets little sun, people with gut conditions that affect absorption, and women who are pregnant or breastfeeding. Go round a family dinner table in Lucknow or Kochi with that list and most people qualify. The grandmother who rarely leaves the flat, the daughter-in-law who is expecting, the son who drives to the office at eight and gets home at nine.
People carrying extra weight are on the list as well. A 2015 meta-analysis in Obesity Reviews found low vitamin D more often in people living with obesity. Vitamin D dissolves in fat, and the usual explanation is that a bigger body spreads it through more fat tissue, so less of it shows up in a blood sample. That says nothing about whether the weight causes the deficiency. It does mean that if you're overweight and also fit one of the groups above, the test belongs on your list.
How is vitamin D deficiency diagnosed?
You need one blood test, serum 25-hydroxyvitamin D, and it's worth asking for it by that name. Holick's review is clear that this is the measure of the body's stores. The similar-sounding 1,25-dihydroxyvitamin D measures the active hormone instead, and it can read normal or even high while stores are low.
Indian labs usually print the right test as "Vitamin D, 25-OH" or "Vitamin D total". It reflects what you've built up from sun and food over the previous few weeks.
By the Endocrine Society's guideline, under 20 ng/mL is deficient and anything between 21 and 29 ng/mL is insufficient. Other expert bodies put the line lower. Labs here don't all print the same reference range either, so a 24 can be flagged red on one report and sit in the normal column on another. Your doctor will read it with your calcium, and sometimes parathyroid hormone, and decide from there how much you need and for how long.
If your lab reports in nmol/L, divide by roughly 2.5; 50 nmol/L is about 20 ng/mL. And note the month on the report. A test taken in a Delhi January often reads lower than the same person's test in October, after months of monsoon and post-monsoon sun.
What actually raises vitamin D?
Your skin makes most of the vitamin D you have, from the UVB in sunlight, and UVB is strongest between late morning and early afternoon. Holick's advice is short, regular exposure of the arms and legs, which works better than an occasional long session. Window glass blocks UVB, so a desk in a bright corner of the office doesn't help. A short walk on the terrace or the society lawn after lunch, sleeves rolled up, is the sort of habit that does.
Diet can only add a little, because few foods contain much vitamin D. On a vegetarian Indian diet the useful ones are milk and cooking oil that say "fortified" on the pack, egg yolks if you eat eggs, and mushrooms that have been exposed to UV light. If your level is clearly low, your doctor will probably suggest a supplement too. Ask what dose, for how long and when to recheck, because vitamin D builds up in the body and too much for too long can do harm.
What does vitamin D have to do with muscle and weight?
If you're planning to lose weight, check your vitamin D first. People living with obesity are more likely to have a low level, as the 2015 Obesity Reviews analysis found, and Gunton and Girgis describe weaker muscles in people who are deficient. The two problems tend to turn up in the same person, at the start of a diet.
That timing is awkward. When you eat less, the body takes some of the lost weight from muscle unless you give it a reason not to. Cava and colleagues, reviewing the trials on this, found two things that protect lean mass: enough protein and regular resistance exercise. In an Indian kitchen the protein part means dal, curd, paneer, chana or eggs at every meal, more than a token katori. The resistance part means squats, lunges and weights every week, and that is hard to keep up if your thighs already ache climbing to the second floor.
We should say where we stand, since you're reading this on our site. Metaboliq is a doctor-led weight programme, and the aim we give members is "Lose up to 20% of your body weight — and keep your muscle". Results vary; your doctor decides what is right for you. Vitamin D is on our ₹1,699 home blood test, read by a doctor with thyroid, sugar and lipids, so a low level gets corrected before the training starts.