Vitamin D, B12, and Iron: What Deficiency Can Look Like

If you’ve been tired, foggy and low for weeks, someone has probably asked whether your vitamins have been checked. It’s a fair question. Low vitamin B12 and low iron can cause fatigue and trouble concentrating, and vitamin D deficiency symptoms, such as muscle aches and bone pain, are easy to lump in with the same picture.

It’s also a question with an honest limit. Finding a deficiency matters for your health, but supplements aren’t a proven treatment for depression, and the research on them is mixed. Here’s what each can look like, who’s more likely to have one, how it’s checked, and what the studies show.

Why These Get Mistaken for Depression

Depression commonly brings low energy, poor concentration and low mood. Low B12 and low iron can cause very similar complaints. Low thyroid and sleep apnea can look similar too.

It also isn’t either/or. A person can have depression and a deficiency at the same time, and finding one doesn’t rule out the other. Inflammation is another question people ask about. Here’s what the research on inflammation and depression shows.

Vitamin B12: The One Not to Put Off

B12 gets its own urgency because long-lasting low levels can damage nerves, and that damage may be permanent if treatment doesn’t start promptly. Some people have no symptoms at all. When symptoms do appear, they can include:

• Body: fatigue, lightheadedness, pale skin, a swollen or red tongue.
• Nerves: numbness or tingling in the hands and feet, loss of balance.
• Thinking and mood: slower thinking, confusion or forgetfulness, and mood or mental changes such as depression or irritability. Severe cases can bring confusion, hallucinations or psychosis.

New numbness, tingling or balance trouble is worth a prompt call to your primary care provider. Sudden numbness or weakness, especially on one side of the body, is different: call 911. B12 can also cause nerve damage even when no anemia develops, so a normal blood count on its own doesn’t settle the question.

Who’s more likely to run low:

• People who eat no animal products, unless they take a supplement.
• Older adults, because lower stomach acid makes B12 from food harder to absorb.
• People with absorption problems: pernicious anemia, Crohn’s disease, celiac disease, or surgery on the stomach or small intestine, including some weight-loss surgeries.
• People who use alcohol, or repeatedly use nitrous oxide (laughing gas).
• People on certain long-term medications. The metformin label warns it may lower B12, and the American Diabetes Association recommends considering periodic B12 checks in people who take metformin long term. The prescription label for omeprazole, a heartburn medicine called a proton pump inhibitor, warns that taking an acid-suppressing medicine daily for a long time (for example, longer than 3 years) may rarely lead to B12 deficiency. The omeprazole label says this applies to any acid-suppressing medicine taken daily over a long time, which would include H2 blockers such as famotidine.

If you take one of these, ask the provider who prescribes it whether a B12 check makes sense. Please don’t stop a medication on your own; some can cause withdrawal symptoms or a return of symptoms if stopped suddenly.

Iron: Stores Can Fall Before Anemia Shows

Iron deficiency anemia develops when your iron stores run low, and symptoms usually start mild and build slowly: feeling weak or tired, headaches, dizziness, trouble concentrating. A 2025 U.S. review adds irritability, low mood, restless legs and pica, a craving for ice or other non-food things.

Not everyone with low iron is anemic. Researchers study this group on its own: people with low iron but no anemia. A ferritin test, which shows how much iron is stored, can add something a blood count doesn’t.

The usual reasons are heavy periods, pregnancy, poor absorption (celiac disease, Crohn’s disease, gastric bypass) and diets low in iron. Bleeding somewhere in the digestive tract is another, sometimes from an ulcer or a cancer. So are regular use of anti-inflammatory pain relievers (NSAIDs) such as ibuprofen and inflammatory bowel disease, and atrophic gastritis, a long-term stomach inflammation that makes iron harder to absorb. So low iron without a clear reason deserves an answer, not just a supplement.

Restless legs belong in this conversation too. That unstoppable urge to move your legs at night is linked with low iron, and the lost sleep can lead to daytime sleepiness, anxiety or depression. Some medications are also linked with it, including lithium and neuroleptics (antipsychotics). The 2025 American Academy of Sleep Medicine guideline and a 2026 U.S. review say serotonergic antidepressants, some antipsychotics and other dopamine-blocking medicines, and sedating antihistamines such as diphenhydramine can make restless legs worse, and the guideline adds alcohol, caffeine and untreated sleep apnea as things to address. Please don’t stop a medication on your own; some can cause withdrawal symptoms or a return of symptoms if stopped suddenly. Talk with your provider before changing anything. In a practice statement based on expert consensus, the same guideline says clinicians should check iron, including ferritin and transferrin saturation, in everyone with clinically significant restless legs, ideally in the morning and after at least 24 hours without iron supplements or iron-rich foods. A ferritin level that counts as “normal” can still be too low for restless legs, so ask for your actual numbers.

Vitamin D: Common, and Easy to Over-Credit

Vitamin D’s main job is helping you absorb calcium, so its classic symptoms show up in bones and muscles: bone pain, muscle weakness or aches, and weak bones and fractures. Low mood isn’t on that list, even though it’s what many people ask about.

You’re more likely to run low if you rarely expose your skin to sunlight, have had weight-loss surgery, have Crohn’s disease, ulcerative colitis or celiac disease, or have kidney or liver disease. Obesity raises the risk too. Some medicines can affect levels, including some seizure medicines and steroids, which interfere with how the body processes vitamin D. Older adults and people with dark skin make less vitamin D from sunlight.

The 2024 Endocrine Society guideline suggests against routine vitamin D testing in healthy adults. Testing makes more sense when there’s a reason, such as low blood calcium, a condition that limits absorption (for example, gastric bypass or inflammatory bowel disease), or medicines that affect vitamin D, so this is a decision for you and your primary care provider. For the seasonal side of the story, see our post on winter and your mood.

Do Supplements Help Mood? What the Research Shows

Well supported: a real deficiency should be treated. That’s true for your nerves, blood and bones, whatever it does for your mood. Anemia from low B12 most often responds well to treatment, and the outlook for iron deficiency anemia is likely good, depending on the cause.

Debated: vitamin D for depression. Low levels are linked with depression, but a link doesn’t show cause. On the supportive side, a review of 41 trials found fewer depressive symptoms with vitamin D, though it rated the certainty of that evidence very low. A review of 31 trials, which rated its evidence moderate, found a benefit that was larger in people who already had depressive symptoms and wasn’t seen in trials lasting longer than about six months.

On the critical side, the VITAL-DEP trial, with more than 18,000 U.S. adults aged 50 and older, found vitamin D didn’t prevent depression or change mood scores over about five years. It tested prevention in people without significant symptoms at the start, so it doesn’t settle whether vitamin D treats depression. A review in older adults found no clear benefit, and the Merck Manual states plainly that it doesn’t effectively treat or prevent depression. The 2022 VA/DoD depression guideline suggests against vitamin D as a treatment for depression, noting that the evidence doesn’t support it on its own, especially without a documented deficiency. Who might benefit isn’t settled either: one review points to people with low levels.

Not supported so far: B12 for people who aren’t deficient. A review of trials in people without overt deficiency found no overall effect on depressive symptoms. Only six of its trials measured mood, mostly B12 given with folic acid, and people with major depression weren’t included. An older review of folate and B12 together found no short-term benefit, with a possible longer-term benefit in a few studies, and it cautioned that trials were few.

Uncertain: iron and mood. Studies disagree on whether blood iron is lower in people with depression: one review found it lower and another found no significant difference, and these studies can’t show cause. In people with low iron but no anemia, a review of trials found supplements eased self-reported fatigue. One trial in menstruating women saw less fatigue but no change in depression scores.

So treat a real deficiency, and don’t count on a supplement to treat depression. If your mood is the main problem, our depression guide covers what has stronger evidence. Our post on nutrition and mental health looks at food and mood more broadly.

More Isn’t Better

Being sold without a prescription doesn’t make these harmless in large amounts.

• Vitamin D. Too much can raise calcium in the blood, which can lead to kidney stones and kidney damage, nausea, vomiting, constipation, poor appetite, weakness and weight loss. It almost always comes from supplements, not sun or food.
• Iron. An overdose can be dangerous, particularly for children, so keep it out of their reach. People with hemochromatosis, a genetic condition, build up harmful iron and shouldn’t take iron supplements.
• B12. It doesn’t appear to be toxic, but the same source says not to take high doses as a cure-all. B vitamin supplements may also affect how certain medicines work.

Tell your providers about everything you take, including gummies and multivitamins. Supplements can affect test results as well as other medicines.

How These Get Checked

All of this usually goes through your primary care provider. We don’t offer primary medical care, so that’s the right person to ask. These are ordinary blood tests:

• B12: a vitamin B12 level, for which you may be asked not to eat or drink first. A methylmalonic acid (MMA) test can help when B12 deficiency is suspected.
• Iron: a complete blood count, ferritin and other iron tests. Ferritin can read high with inflammation, so it’s read alongside the rest of your health.
• Vitamin D: a 25-hydroxyvitamin D test, the most accurate way to see whether you have enough.

It’s reasonable to ask for your actual numbers, not just “normal.” Labs use different ranges, and normal levels with ongoing symptoms may call for other tests.

Where a Psychiatric Evaluation Fits

A psychiatric evaluation with one of our providers looks at your symptoms alongside your sleep, energy and medical and treatment history, and that’s where these questions come up. For adults in South Jersey and across New Jersey, it’s a way to step back and ask whether something medical might be part of the picture, and to take that question to your primary care provider if so.

A low result doesn’t always explain everything. Some people may feel much better once a deficiency is corrected. Others still have depression that needs its own care, and that isn’t a failure.

Frequently Asked Questions

What are the symptoms of vitamin D deficiency?

Low vitamin D doesn’t always cause symptoms. When deficiency is severe, the main ones are bone pain, muscle weakness or aches, and weak bones that break more easily. Many people ask about low mood, but it isn’t one of the symptoms MedlinePlus lists, and research on the connection is debated.

Can low B12 cause depression or anxiety?

The National Heart, Lung, and Blood Institute lists mood or mental changes, such as depression or irritability, among the symptoms of vitamin B12 deficiency, along with slower thinking, confusion and forgetfulness. Numbness, tingling or balance problems make it more urgent to get checked, because nerve damage can become permanent.

Can you have low iron without being anemic?

Yes. Iron stores can be low while your blood count is normal, and a ferritin test helps show this. Trials in this group found supplements eased self-reported fatigue, though the effect on depression is less clear.

Does vitamin D help with depression?

It’s debated. Some reviews of trials find a small benefit: one rated its evidence very low, while another rated it moderate and found a larger effect in people with depressive symptoms. A large U.S. trial found it didn’t prevent depression. Correcting a real deficiency is worthwhile for your health, but it shouldn’t replace depression treatment.

What blood tests should I ask about if I’m tired all the time?

Ask your primary care provider which make sense for you. Common ones include a complete blood count, thyroid tests, B12 and ferritin, with vitamin D if you have a reason to check it, since the Endocrine Society suggests against routine testing in healthy adults.

If fatigue and low mood have been hanging around, a psychiatric evaluation can help sort out what’s going on, and medication management gives you regular follow-ups if treatment becomes part of the plan.

This article is for general educational purposes only. It does not constitute medical advice, does not establish a provider-patient relationship, and is not a substitute for individual evaluation, diagnosis, or treatment by a qualified clinician. If you’re in crisis or thinking about harming yourself, call or text 988 (Suicide & Crisis Lifeline), any time, day or night. In an emergency, call 911 or go to the nearest emergency room.