Low vitamin D3 usually shows up as bone aches, weak thighs and tiredness. Low B12 shows up as exhaustion, breathlessness, a sore tongue, and tingling or numbness in the feet and hands. Plenty of people have no symptoms at all, so the only way to know is a blood test. Treatment is simple once you know. For vitamin D, doctors usually give a high dose for about 8 weeks, then a smaller daily dose to keep you topped up. For B12, a daily tablet of around 1,000 µg works for most people. Injections are kept for severe cases, nerve symptoms, or people who can't absorb B12 from food. Retest after about three months.
- Test for D3
- 25(OH)D blood test
- Test for B12
- Serum B12 (+ MMA if borderline)
- Usual D3 fix
- High dose ~8 weeks, then maintenance
- Usual B12 fix
- ~1,000 µg a day by mouth
- Injections for
- Severe cases, nerve symptoms, poor absorption
- Retest
- After about 3 months
The symptoms, side by side
Let's get one thing out of the way first. You can be quite low in either vitamin and feel completely normal. Lots of people find out only because a routine health package flagged it. So treat this list as "reasons to get tested", not as a way to diagnose yourself.
| Symptom | Low D3 | Low B12 |
|---|---|---|
| Tiredness | Common | Very common |
| Bone pain, aching back or legs | Yes | Not typical |
| Weak hips and thighs | Yes | Not typical |
| Breathless on stairs | Not typical | Yes, from anaemia |
| Pale or yellowish skin | No | Yes |
| Sore, red, smooth tongue | No | Yes |
| Tingling or numb feet and hands | No | Yes, can be the first sign |
| Unsteady walking | From weak muscles | From nerve damage |
| Memory, mood, brain fog | Unclear | Yes |
The vitamin D signs come from weak bones and muscles.1 The B12 signs come from anaemia and from nerves losing their protective coating.4 If you want the full story of what's going on inside, part 1 of this series walks through it.
Low iron, thyroid problems, poor sleep, depression and plain old overwork all cause the same exhaustion. That's one more reason to test instead of guessing. Ask for a blood count, iron studies and thyroid tests alongside vitamin D and B12.
How to read your report
This is where people get confused, because labs print different "normal" ranges and even the experts don't fully agree. Here's a practical way to read the two numbers.
Vitamin D: the 25(OH)D number
| Your result | What it usually means |
|---|---|
| Below 20 ng/mL (50 nmol/L) | Deficient. Most guidelines agree this needs treating.2,3 |
| 20–29 ng/mL | A grey zone. The Institute of Medicine treats 20 as enough for most people; the Endocrine Society's 2011 guideline called this "insufficient".2,3 |
| 30 ng/mL and above | Comfortably sufficient. |
Your report might be in nmol/L instead. To convert, divide by 2.5. So 50 nmol/L is 20 ng/mL. And one more thing worth knowing: in 2024 the Endocrine Society said healthy adults under 75 don't need routine vitamin D testing at all.4 If you've got symptoms, are pregnant, older, or in a high-risk group, testing still makes sense.
B12: the serum B12 number
Below roughly 200 pg/mL is usually treated as deficient. Between about 200 and 300 is the awkward middle, where some people are genuinely short and others are fine.5 In that range, your doctor can order methylmalonic acid (MMA) or homocysteine. Both rise when your cells really are running low on B12, so they help settle the question.5,6
How low vitamin D3 is treated
Treatment usually happens in two stages. First you fill the tank, then you keep it from emptying again.
- The loading phase. The Endocrine Society's guideline for deficient adults is 50,000 IU once a week for 8 weeks, or about 6,000 IU every day.2 In India, doctors commonly prescribe the 60,000 IU sachet or capsule once a week for around 8 weeks, which is roughly the same idea.
- The maintenance phase. After that, a smaller regular dose keeps your level up. For adults at risk, the same guideline suggests 1,500–2,000 IU a day.2
- Take it with a meal that has some fat in it. Vitamin D is fat-soluble, so it absorbs better with food than on an empty stomach.
- Retest after about three months to check it actually worked, and adjust from there.
The loading dose is meant for a limited time. For everyday supplementing without medical supervision, the upper limit for adults is 4,000 IU a day.3 Too much vitamin D raises calcium in the blood, which can cause nausea, vomiting, confusion and kidney problems. Our research note on the 60,000 IU weekly sachet explains why it's become such an Indian habit, and where it goes wrong.
What about the sun? It helps, and getting some midday sun on your arms and legs a few times a week is a good habit. But if you're already deficient, sunlight alone is slow and hard to dose, especially with indoor work and darker skin. Most people need the supplement to get back up, then sun and a maintenance dose to stay there.
How low B12 is treated
Most people assume B12 means injections. Often it doesn't.
A Cochrane review compared tablets with injections and found that 1,000 µg a day by mouth brought blood B12 back to normal about as well as injections did, and cost less.7 The evidence was rated low quality, because the trials were small, but it matches what many doctors now do in practice. It works because a small fraction of a big oral dose gets absorbed even without the usual stomach machinery.
Injections still have a clear place, though. Your doctor will usually choose them if:
- You already have nerve symptoms, like numbness, tingling or balance problems, and they want your levels up fast
- The deficiency is severe, with significant anaemia
- You can't absorb B12 properly, for example with pernicious anaemia or after certain stomach or bowel surgery5
How fast will you feel better? Energy and breathlessness often start improving within a few weeks as new healthy blood cells come through. Nerve symptoms are slower. Give them months, and they may not fully go away if they'd been there a long time.5 Methylcobalamin and cyanocobalamin both work, by the way. Our methylcobalamin page compares the forms.
High-dose folic acid can fix the anaemia caused by low B12, so your blood count looks better, while the nerve damage carries on underneath.5 If you're being treated for anaemia, make sure B12 has actually been checked.
Can food fix it?
For prevention, food matters a lot. For fixing an existing deficiency, it's usually not enough on its own.
- B12: milk, curd, paneer, eggs, fish, chicken and meat. If you're vegetarian, dairy every day helps, and B12-fortified foods help more. If you're vegan, a supplement isn't optional.
- Vitamin D: very few foods have much. Fatty fish, egg yolks and fortified milk or oils give a little. That's exactly why sunlight and supplements end up doing most of the work.
Common mistakes to avoid
- Stopping as soon as you feel better. Feeling better isn't the same as your levels being back to normal. Finish the course and retest.
- Never retesting. Without a follow-up test you don't know if the dose worked, or if you've overshot.
- Treating one and ignoring the other. It's very common in India to be low in both.
- Waiting out tingling feet. That's the one symptom not to sit on. See a doctor.
Get tested. If you're low, follow a proper course rather than a random supplement. Take vitamin D with food. Retest in about three months. Then keep things topped up with a sensible daily dose, some sun, and B12 from food or a tablet. That's genuinely it.
Frequently asked questions
What are the symptoms of vitamin D3 and B12 deficiency?
Low vitamin D3 tends to cause bone pain, aching legs or back, weak hips and thighs, and tiredness. Low B12 causes tiredness, breathlessness, pale skin, a sore smooth tongue, and tingling or numbness in the feet and hands, sometimes with balance or memory problems. Many people have no symptoms, so a blood test is the only reliable check.
How is vitamin D3 deficiency treated?
Usually with a high loading dose for about 8 weeks, such as 50,000–60,000 IU once a week or around 6,000 IU a day, followed by a maintenance dose of about 1,500–2,000 IU a day. Take it with food and retest after about three months. The dose should come from your doctor based on your blood level.
Are B12 tablets as good as injections?
For most people, yes. A Cochrane review found that 1,000 µg of B12 a day by mouth raised blood levels about as well as injections, at lower cost, though the evidence was low quality. Injections are still preferred for severe deficiency, nerve symptoms, or conditions where B12 can't be absorbed.
How long does it take to recover from B12 deficiency?
Energy and breathlessness often improve within a few weeks of starting treatment. Nerve symptoms such as tingling and numbness take months to improve, and may not go away completely if they were present for a long time before treatment.
Can I take 60,000 IU vitamin D every week?
Only for a limited course prescribed by your doctor, usually about 8 weeks, followed by a lower maintenance dose. For ongoing use without supervision, the adult upper limit is 4,000 IU a day. Taking very high doses for months can raise blood calcium and harm your kidneys.
What B12 level is considered low?
Below about 200 pg/mL is usually treated as deficient. Between about 200 and 300 pg/mL is borderline, and a methylmalonic acid (MMA) or homocysteine test helps confirm whether you're truly short.
This article is general information, not medical advice. Doses and treatment should be decided by your doctor based on your blood results, especially if you're pregnant, have kidney problems or take regular medication.
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