Vitamin D3 is how your body gets calcium out of food and into your bones. Without it, even a calcium-rich diet does little for your skeleton, and muscles get weaker too. B12 is needed to make healthy red blood cells and to protect your nerves. It also matters a lot before and during pregnancy. ICMR recommends 600 IU of vitamin D and 2.2 µg of B12 a day for adults. B12 comes almost only from animal foods, and very few foods have much vitamin D, which is why the sun and, for many people, supplements end up mattering so much.
- D3's main job
- Calcium absorption for bones
- B12's main job
- Red blood cells and nerves
- Adult need (ICMR 2020)
- D: 600 IU · B12: 2.2 µg
- Best D source
- Sunlight on skin
- Best B12 sources
- Dairy, eggs, fish, meat
- Don't expect
- Extra D to prevent heart disease or cancer
What vitamin D3 does for you
Calling vitamin D a vitamin is a bit misleading. Your skin makes it when sunlight hits it, and your liver and kidneys then turn it into an active form that behaves like a hormone.1 So it's really more of a signal than a nutrient.
The signal's most important message goes to your gut: absorb more calcium and phosphorus. With enough vitamin D, your intestines pull in a reasonable share of the calcium you eat. Without it, only about 10–15% gets absorbed.1 That matters because calcium is what makes bones hard, and your body is constantly breaking down and rebuilding bone throughout your life.
Here's what that adds up to:
- Strong bones and teeth. In children, enough vitamin D is what lets bones grow straight and hard. Too little causes rickets. In adults, too little leads to soft bones (osteomalacia) and faster bone loss with age.1
- Working muscles. Weak hip and thigh muscles are a known feature of low vitamin D. For older people that means more falls.1
- Calcium balance. Your heart and nerves need blood calcium kept in a tight range. Vitamin D is part of the system that keeps it there.
You'll often read that vitamin D also protects your heart, prevents cancer and boosts immunity. Be a little careful with that. Cells all over the body do respond to vitamin D, but when researchers actually tested it, the results were underwhelming. In the large VITAL trial, older adults in the US who took 2,000 IU a day for years didn't get less cancer or fewer heart attacks and strokes than people on a placebo.6 Vitamin D clearly matters for bones and muscles. For most other things, the honest answer is "not proven".
What B12 does for you
B12 has a quieter reputation, but it's involved in some pretty fundamental work.2,3
Building new red blood cells
Every red blood cell starts with a fresh copy of DNA, and B12 is needed to make it. Your marrow turns out enormous numbers of these cells every day, so even a modest shortage shows up as anaemia eventually.
Protecting your nerves
B12 helps maintain myelin, the fatty coating that lets signals travel along your nerves properly. That's why long-term deficiency causes tingling, numbness and balance problems.
It also helps clear homocysteine, a by-product your body makes every day. When B12 is low, homocysteine builds up, and high levels are linked to heart and blood vessel problems.3
And then there's pregnancy. B12 works together with folate while a baby's brain and spine are forming in the first weeks, often before a woman even knows she's pregnant. In a large study, mothers with the lowest B12 had two to three times the odds of a pregnancy affected by a neural tube defect compared with mothers with the highest.7 That's a strong reason for women planning a baby to check B12 early, especially vegetarians.
B12 in food is bound to protein. Stomach acid has to free it, then a protein from your stomach called intrinsic factor carries it to the end of your small intestine, where it's absorbed.3 Anything that disrupts that chain, like ageing, long-term acid-reducing tablets or stomach surgery, can leave you low even if you eat enough.
How much do you need each day?
In 2020, ICMR and the National Institute of Nutrition updated India's nutrient requirements. For adults, men and women alike, the numbers are:4
| Nutrient | Average requirement (EAR) | Recommended (RDA) | Old RDA (2010) |
|---|---|---|---|
| Vitamin D | 400 IU | 600 IU | 400 IU |
| Vitamin B12 | 2 µg | 2.2 µg | 1 µg |
| Calcium | 800 mg | 1,000 mg | 600 mg |
Notice that all three went up from the 2010 numbers. The EAR is the amount that meets the needs of about half of healthy people, and it's what ICMR now suggests for planning diets. The RDA is set higher, so that almost everyone is covered.4 These are amounts to stay healthy. If you're already deficient, treatment doses are much higher for a while, which we cover in part 2 of this series.
Where you actually get them
Here's how much is in some everyday foods, per 100 g, from USDA data.5
| Food (100 g) | B12 | Vitamin D |
|---|---|---|
| Sardines, canned | 8.9 µg | 193 IU |
| Mackerel (Atlantic), raw | 8.7 µg | 643 IU |
| Salmon, cooked | 2.8 µg | 526 IU |
| Whole egg | 0.9 µg | 82 IU |
| Milk | 0.45 µg | Only if fortified |
| Cottage cheese (closest to paneer) | 0.43 µg | Very little |
| Curd | 0.37 µg | Very little |
| Chicken breast, cooked | 0.34 µg | Very little |
| Mushrooms, UV-exposed | 0 | 1,050 IU |
| Dal, rice, roti, vegetables | 0 | 0 |
A few things jump out.
B12 is easy for fish and egg eaters, harder for vegetarians. A small portion of sardines or mackerel covers several days' worth. Vegetarians can get there with dairy, at least on paper: two glasses of milk (about 500 ml) give roughly 2.2 µg. But plenty of people don't drink that much milk every day, and vegans get none at all from food. Plant foods simply don't contain B12, so fortified foods or a supplement are the realistic option.2
Vitamin D is hard to get from food, full stop. Oily fish and UV-treated mushrooms are the only rich sources. US milk has vitamin D added, which is where that number comes from. In India, milk only has it if the pack says fortified (look for the "+F" logo). That's why your skin, and the sun, end up doing most of the work.1
The sun is your main vitamin D source
When UVB light reaches your skin, it converts a cholesterol-like compound into vitamin D3.1 Most people get far more vitamin D this way than from food. But it depends on a lot of things: the time of day (UVB is strongest around midday), how much skin is uncovered, how dark your skin is, how polluted the air is, and whether you're behind glass, which blocks UVB.
So "India is sunny" doesn't automatically mean "Indians have enough vitamin D". Far from it, actually, and that's what our vitamin D3 page and part 4 of this series dig into.
Vitamin D3 keeps your bones and muscles strong. B12 keeps your blood and nerves healthy, and protects babies before they're even born. You need small amounts of both, every day, for life. Get some sun, eat B12 foods if you can, and if you can't, a test and a supplement are cheap insurance.
Frequently asked questions
Why is vitamin D3 important?
Vitamin D3 lets your gut absorb calcium and phosphorus, which your body needs to build and maintain strong bones and teeth. It also supports muscle strength. Without enough, children can develop rickets, and adults can develop soft bones, faster bone loss and weak muscles.
Why is vitamin B12 important?
B12 is needed to make DNA for new red blood cells and to maintain the protective coating on your nerves. Low B12 can cause anaemia and nerve damage. It's also important before and during pregnancy, because low B12 is linked to a higher risk of neural tube defects in the baby.
How much vitamin D3 and B12 do I need a day?
ICMR-NIN 2020 recommends 600 IU of vitamin D and 2.2 µg of vitamin B12 a day for Indian adults, men and women alike. These are maintenance amounts for healthy people. If you're deficient, your doctor will prescribe higher treatment doses for a limited time.
Which foods are high in vitamin D3 and B12?
Oily fish such as sardines and mackerel are rich in both. Eggs have some of each. Milk, curd and paneer provide B12 but little vitamin D unless the milk is fortified. UV-exposed mushrooms provide vitamin D but no B12. Dal, rice, roti and vegetables contain neither.
Can vegetarians get enough B12 from food?
It's possible with plenty of dairy, since about two glasses of milk give roughly the daily requirement, but many vegetarians don't eat that much. Plant foods contain no B12, so vegans and anyone eating little dairy usually need fortified foods or a supplement.
Does vitamin D prevent heart disease or cancer?
Not on current evidence. In the large VITAL trial, older adults taking 2,000 IU a day had no fewer cancers or major heart events than those on placebo. Vitamin D's proven benefits are for bones and muscles, and for correcting deficiency.
This article is general information, not medical advice. If you're pregnant, planning a pregnancy or have a health condition, talk to your doctor about your vitamin D and B12 needs.
References
Disclosures: No manufacturer provided funding for this article, and it contains no sponsored or affiliate links. The banner features an AI-generated presenter, not a real doctor or patient. Full policy: conflicts policy