Vitamin D (D2 and D3): ICMR-NIN Value in IU, Sunlight, Fortified Foods and Testing

Vitamin D is the one vitamin the body makes for itself, in skin exposed to sunlight, and the one Indian diets supply least of. It is needed to absorb calcium and to mineralise bone. ICMR-NIN's Nutrient Requirements for Indians 2020 sets the allowance at 600 IU a day, which is 15 mcg, for adults and for children from one year, and at 800 IU from the age of 60, with a tolerable upper limit of 4,000 IU. This entry in the vitamins section of the handbook covers sunlight, the two forms, fortified milk and oil, the Indian studies, the blood test, and why large doses belong with a doctor.

What is vitamin D and what does it do?

It is a fat-soluble vitamin whose best-established job is to let the gut absorb calcium. ICMR-NIN's 2024 Dietary Guidelines put it in one line: exposure to sunlight maintains vitamin D status, which helps in calcium absorption. When the supply fails, bone is the tissue that suffers. A 2018 review from the All India Institute of Medical Sciences describes the result as rickets in children, with defective mineralisation and skeletal deformity, and osteomalacia and osteoporosis in adults, with muscle weakness, bone pain and a higher risk of falls.

The same guidelines note that older people are at increased risk of osteomalacia, which they define as defective bone mineralisation due to lack of exposure to sunlight and poor diet. Low vitamin D has also been associated with heart disease, diabetes, infections and several cancers, but an association is not proof, and the trials described further down tested the question directly. The handbook's calcium entry covers the mineral vitamin D works with.

Sunlight, D2 and D3: where vitamin D comes from

There are three routes. The first is the skin: the AIIMS review states that about 90 per cent of the vitamin D a person needs is synthesised in skin under sun exposure, and the 2024 guidelines add that cholesterol is the starting material. The second is animal food, which carries cholecalciferol, vitamin D3. The third is ergocalciferol, vitamin D2, the form found in plants and fungi.

Timing matters more than most people expect. A study at Tirupati exposed sealed ampoules of the skin's precursor compound to sunlight every hour from 8 am to 4 pm for over a year, and found that formation of previtamin D3 was greatest between 11 am and 2 pm in every season. ICMR-NIN's 2024 guidelines advise children and adolescents to get about 30 minutes of sunlight, preferably between 11 am and 2 pm, and tell pregnant women to expose themselves to direct sunlight for at least 15 minutes.

How much vitamin D do you need in India?

ICMR-NIN's 2020 allowance is 600 IU a day for men, women, adolescents and children, with an estimated average requirement of 400 IU. That is a rise from the 400 IU allowance of 2010, and the expert group gave its reason: sunlight exposure has been falling, so more has to come from the diet. It still emphasised outdoor physical activity as the means of achieving adequate status. FSSAI's standard converts 1 IU to 0.025 mcg, so 600 IU is 15 mcg.

The allowance does not rise in pregnancy or lactation, and it is the same for both sexes. The average requirement is 400 IU in every group for which one is given, including people over 60. The upper limit, the maximum habitual intake from all sources judged unlikely to cause harm, is 4,000 IU, or 100 mcg, a day for adults.

Which Indian foods contain vitamin D?

Very few, and almost all of them are animal foods: oily fish, liver, egg and, in traces, milk. The Indian Food Composition Tables 2017 report vitamin D, which many food composition databases lack. The table below converts their cholecalciferol (D3) values per 100 g into household portions and into IU at FSSAI's rate of 40 IU to the microgram.

A 100 g piece of hilsa, the Bengali ilish, supplies about a third of the allowance, which makes it the outstanding everyday source in the tables, while one whole egg and a glass of plain milk together supply under 30 IU. For a vegetarian the list is nearly empty. The tables do report ergocalciferol (D2) in plant foods, measured, they say, for the first time anywhere: 13.43 mcg per 100 g in whole wheat atta and 20.54 mcg in fresh button mushroom. These are new laboratory values, and a roti-eating population that still tests low gives reason not to rely on them.

What does FSSAI's fortification standard add to milk and oil?

Where milk or vegetable oil is sold as fortified, FSSAI's Fortification of Foods regulations fix how much vitamin A and D it must carry. Fortified milk of any type, from full cream to skimmed, must hold 5 to 7.5 mcg of vitamin D per litre, and fortified oil 0.11 to 0.16 mcg per gram. The regulations allow cholecalciferol or ergocalciferol, in both cases only from a plant source.

To know whether a pack is fortified, read it. The regulations require every package of fortified food to carry the words "fortified with" followed by the name of the nutrient, together with the official fortification logo; a pack without them should be assumed to be plain. ICMR-NIN's guidelines note that their own food tables give values for unfortified milk and oil. The page on milk in the Indian food tables has its full panel.

Too little: deficiency in Indian studies and surveys

Low vitamin D is common in India despite the sunshine. The AIIMS review of published Indian studies found a prevalence of deficiency ranging from 40 to 99 per cent, with most studies reporting 80 to 90 per cent, generally using a blood level below 20 ng/mL as the cut-off; community studies of apparently healthy people ranged from 50 to 94 per cent. In Delhi, a study of schoolchildren aged 10 to 18 found levels below 9 ng/mL in 35.7 per cent of those tested and clinical evidence of deficiency in 10.8 per cent of 5,137 children examined.

National survey figures for children are lower, and studies with different cut-offs cannot be compared directly. The Comprehensive National Nutrition Survey of 2019, as tabulated in ICMR-NIN's 2024 guidelines, found vitamin D deficiency in 13.7 per cent of children aged 1 to 4, 18.2 per cent at 5 to 9 and 23.9 per cent at 10 to 19 years. The review lists the causes: indoor living, air pollution that hampers synthesis in skin, darker skin, sunscreen, covering clothing, few animal foods in the diet and little fortified food. The article on why a sunny country runs short of vitamin D takes these in turn.

How is vitamin D tested?

The test is a blood measurement of 25-hydroxyvitamin D, written 25(OH)D, the form that circulates in blood. The AIIMS review calls it the most useful measure of status and gives its half-life as about three weeks, so a result reflects recent weeks of sun and intake and shifts with the season. The active hormone, 1,25-dihydroxyvitamin D, is not used for this purpose because calcium, phosphate and parathyroid hormone control its level.

A doctor investigating bone symptoms may order calcium, phosphorus, alkaline phosphatase and parathyroid hormone alongside, the panel the Delhi researchers used. Cut-offs differ between bodies, and what a figure means for you is the doctor's call; the site's guide to reading a vitamin D report explains the ranges laboratories print. The Endocrine Society's 2024 guideline found no trial evidence to support routine screening of healthy people and suggests against testing without an established reason.

What does the evidence say about vitamin D supplements?

For healthy adults who are not selected for deficiency, large trials have found little. VITAL randomised 25,871 American men and women to 2,000 IU of vitamin D3 a day or placebo for a median of 5.3 years. Cancer was no less common (hazard ratio 0.96) and nor were major cardiovascular events (0.97). A later report from the same trial found no significant effect on total fractures (0.98) or hip fractures. This is strong evidence, with the limit that the participants were American and were not chosen for being deficient.

The Endocrine Society's 2024 guideline reads the trial evidence the same way. It suggests against supplements above the reference intake for healthy adults under 75, and suggests them for children and adolescents aged 1 to 18 to prevent nutritional rickets, for people of 75 and over, in pregnancy, and in high-risk prediabetes. For those over 50 who do need vitamin D, it favours daily amounts over intermittent high doses. On form, a meta-analysis of trials found D3 raised blood levels more than D2 when given as a large single dose, a difference that disappeared with daily dosing.

A worked example: an indoor worker's day in Kolkata

This is an illustration, not a real person. Take a 34-year-old vegetarian bank employee in Kolkata who leaves home at 8 am and returns after dark. Her allowance is 600 IU. If her two glasses of milk and her 20 g of cooking oil are both fortified to FSSAI's standard, food gives her 168 to 248 IU. If neither is, two glasses of plain milk give about 20 IU. In both cases most of the 600 IU has to come from skin, and her skin sees no midday sun on a working day.

If she ate fish, a 100 g piece of hilsa would add about 198 IU on the day she ate it, and a pot of Kerala fish curry made with sardine about 140 IU per 100 g of fish. No ordinary vegetarian plate reaches 600 IU, fortified staples cover two fifths at best, and the rest depends on time outdoors.

Common mistakes and myths about vitamin D

The second mistake is to count early-morning sun as enough: in the Tirupati measurements the productive hours were around midday. The third is to assume a higher blood level is always better and take a sachet every week without a prescription. The fourth is to expect a supplement to prevent cancer, heart disease or fractures in a healthy adult, which the large trial did not find. The fifth is to forget calcium, covered in calcium-rich Indian foods.

Too much vitamin D, megadoses and when to see a doctor

Sunlight and food do not take anyone past ICMR-NIN's upper limit of 4,000 IU a day; supplements and injections can. Vitamin D raises calcium absorption, so an overdose shows up as high blood calcium. Doctors in Kashmir reported ten adults with vitamin D intoxication after high doses prescribed for various ailments: they had vomiting, excessive urination and thirst, confusion and kidney dysfunction, and all had high calcium.

That is why a sachet or injection of several thousand or lakh IU is a prescription matter. The dose, the interval and the length of the course are for a doctor to set against a blood level. Nobody should give an infant or child an adult preparation: the upper limit for a baby under six months is 1,000 IU a day. People with kidney disease need medical advice before any vitamin D supplement.

Studying this with NNWA

Vitamin D comes up in NNWA's teaching under micronutrients, bone health and nutrition through the life cycle. NNWA is a private skill academy based in Kolkata, with classes online in English and Hindi. Its courses train people to coach healthy clients and pass medical cases to a doctor; not one of them is a degree or a dietitian qualification. The Clinical Nutrition and Dietetics course deals with reports and clinical conditions, and the Diploma in Nutrition, Dietetics and Public Health covers requirements and diet planning.