I keep seeing the same pattern.

Someone feels tired all the time, maybe a little foggy, their mood is off, workouts feel harder than they should. They do the usual stuff. More coffee. Earlier bedtime. A new supplement that a friend swears by.

And months later they are still not quite right.

Two nutrient deficiencies show up in that exact story more than you would think. Vitamin B12 and vitamin D. Not because they are trendy. Because they are quietly involved in a lot of basic systems that you notice the moment they start slipping.

This is not a diagnose yourself post. It is a fast checklist to help you figure out if you are even in the risk zone, so you know whether it is worth asking for labs, or taking the issue seriously instead of brushing it off as just stress.

Also, quick note. You can be low in both at the same time. It happens. And the symptoms can overlap enough that guessing is kind of useless.

So let’s do this in a clean way.

The 30 second version (what B12 and D actually do)

Vitamin B12 supports red blood cell production, DNA synthesis, and nerve function. When it is low, people often feel fatigue, weakness, numbness or tingling, brain fog, balance issues, and sometimes mood changes.

Vitamin D acts more like a hormone than a typical vitamin. It affects bone health, muscle function, immune regulation, and inflammation. When it is low, people often report fatigue, low mood, frequent illness, muscle aches, bone pain, and general “I feel off” vibes that are hard to describe.

Neither of these is rare. And both can be missed if nobody thinks to test.

Before the checklist, one important thing

Symptoms alone are not enough.

You can have classic symptoms and be normal on labs. You can also have barely any symptoms and still be low. So treat this like a risk screener. If you check enough boxes, the smart move is to ask your clinician for testing.

Also, do not megadose because a checklist made you nervous. Get a baseline first if you can, especially for vitamin D since levels can go too high if you overdo it for long enough.

Ok. Checklist time.

Give yourself 1 point for each “yes”. Some items are worth 2 points. I will mark those.

At the end I will show you how to interpret it.

A. Diet and lifestyle risk (B12)

• You are vegan or mostly vegan (2 points)
• B12 is naturally found in animal products. Fortified foods and supplements can cover it, but if you are not consistent, risk climbs fast.
• You are vegetarian and do not eat much dairy or eggs (1 point)
• You rarely eat animal foods (1 point)
• Even if you are not officially vegetarian, low intake over time can matter.
• You are pregnant or breastfeeding (1 point)
• Needs can increase, and baby depends on maternal status.
• You are over 50 (1 point)
• Absorption tends to decline with age, partly due to stomach acid changes.

B. Gut and absorption risk (B12)

This is the big one. Many B12 issues are not intake. They are absorption.

• You have chronic digestive symptoms (bloating, diarrhea, constipation, unexplained stomach issues) (1 point)
• You have been diagnosed with celiac disease, Crohn’s disease, ulcerative colitis, or other inflammatory bowel disease (2 points)
• You have had bariatric surgery or other stomach or intestinal surgery (2 points)
• You have a history of gastritis, ulcers, or H. pylori (1 point)
• You have pernicious anemia in your family, or you have been told you have intrinsic factor issues (2 points)

C. Medication risk (B12)

These are common, and people forget they matter.

• You take metformin (for type 2 diabetes or insulin resistance) (2 points)
• Long term use is associated with lower B12 in a meaningful number of people.
• You take acid reducing medication often (PPIs like omeprazole, esomeprazole, lansoprazole, or H2 blockers like famotidine) (1 point, 2 points if daily for months)
• Stomach acid helps release B12 from food.
• You regularly use antacids (1 point)

D. Symptom clues (B12)

These do not prove deficiency, but they are worth noting. Some are more specific.

• Persistent fatigue or low energy that does not match your sleep (1 point)
• Brain fog, memory issues, or trouble concentrating (1 point)
• Tingling, numbness, burning, or pins and needles in hands or feet (2 points)
• This is one of the red flag patterns.
• Balance issues, clumsiness, or feeling unsteady (2 points)
• Unusual tongue soreness, mouth ulcers, or a smooth or “burning” tongue (1 point)
• Shortness of breath with mild exertion, paleness, or feeling weak (1 point)
• Can overlap with iron deficiency too, so do not assume.
• Mood changes, irritability, low mood, or anxiety that feels new or unexplained (1 point)
• You have been told you have anemia, enlarged red blood cells, or high MCV (2 points)

Quick B12 score interpretation

• 0 to 2 points: lower risk, but not impossible. If symptoms are strong, still consider testing.
• 3 to 5 points: moderate risk. Testing is a good idea.
• 6+ points: higher risk. Testing becomes hard to justify skipping.

If you scored high because of neurologic symptoms like tingling or balance issues, do not wait forever. Nerve issues can become harder to reverse the longer they go on.

Same deal. 1 point each, some 2 point items.

Vitamin D status is heavily shaped by sun exposure, skin tone, location, and routine. So the checklist leans that way.

A. Sun and geography risk (Vitamin D)

• You live far from the equator (northern US, Canada, UK, much of Europe, etc) (1 point)
• Winter UVB can be too weak for vitamin D production in many regions.
• It is winter where you live for several months (1 point)
• You work indoors most days and rarely get midday sun (2 points)
• Not morning sun. Not through glass. The UVB that drives D production is basically blocked by windows.
• You wear sunscreen diligently or cover most skin when outside (1 point)
• Sunscreen is important for skin cancer prevention. This is not a “stop using sunscreen” argument. It is just a risk factor for low D.
• You have darker skin (1 point, sometimes 2 depending on sun exposure)
• Melanin reduces vitamin D synthesis from sunlight, so you may need more sun exposure to produce the same amount.
• You avoid the sun or burn easily and therefore do not spend much time outside (1 point)

B. Body and health risk (Vitamin D)

• You have a higher body fat percentage or obesity (1 point)
• Vitamin D is fat soluble and can be sequestered in fat tissue, lowering circulating levels.
• You are older (60+) (1 point)
• Skin produces less vitamin D with age.
• You have osteoporosis, osteopenia, or a history of fractures (2 points)
• You have chronic kidney disease or liver disease (2 points)
• These organs are involved in vitamin D activation and metabolism.
• You have malabsorption issues (celiac, IBD, pancreatic problems, bariatric surgery) (2 points)

C. Diet and supplementation risk (Vitamin D)

• You rarely eat vitamin D rich foods (fatty fish like salmon, sardines, fortified dairy or alternatives, fortified cereals) (1 point)
• You do not take any vitamin D supplement and you get minimal sun (2 points)
• You are exclusively breastfeeding without infant vitamin D drops for baby (or nobody has talked about it) (1 point)
• This is a baby focused point. Breast milk is usually low in vitamin D unless maternal levels are high.

D. Symptom clues (Vitamin D)

Again, symptoms overlap with lots of things. But patterns matter.

• Frequent infections or you feel like you catch everything (1 point)
• Muscle weakness, heaviness, or aches that do not have a clear reason (1 point)
• Bone pain or deep aches, especially in back, hips, legs (2 points)
• Fatigue that feels physical, not just sleepy (1 point)
• Low mood, seasonal sadness, or depressive symptoms (1 point)
• Interestingly, low vitamin D levels have been linked to mood disorders.
• Slow recovery from workouts, or more soreness than usual (1 point)

Quick Vitamin D score interpretation

• 0 to 2 points: lower risk.
• 3 to 5 points: moderate risk. Testing is reasonable, especially if symptoms exist.
• 6+ points: high risk. Testing is strongly worth considering.

People ask this a lot, so here is the messy truth. If you have these combinations, B12 and D both deserve a look.

You might be at risk for both if you have:

• Fatigue plus low mood plus brain fog, and you also have low sun exposure.
• Numbness or tingling plus low energy, especially if you are vegetarian or on metformin.
• Frequent illness plus muscle aches plus indoor lifestyle.
• Digestive issues plus fatigue, because gut problems can mess with absorption for multiple nutrients.
• A history of bariatric surgery, because that hits absorption broadly.

If you scored moderate or high on both checklists, do not try to guess which one is “the real issue”. Test both. It is common to find one low and the other borderline. Or both low.

This matters, because testing can be done badly, especially for B12.

For vitamin B12

Ask about:

• Serum B12 (common starting test)
• Methylmalonic acid (MMA) (helps detect functional B12 deficiency, often more sensitive)
• Homocysteine (can be elevated in B12 or folate deficiency)
• CBC (complete blood count) with indices like MCV

If your B12 is “low normal” but you have symptoms, that is where MMA and homocysteine can help clarify.

Also worth mentioning. Folate status can mask some blood signs of B12 deficiency while nerve issues continue. This is one reason clinicians take neurologic symptoms seriously.

For vitamin D

Ask for:

• 25 hydroxy vitamin D (25(OH)D)
• This is the standard blood test for vitamin D status.

Try not to get sidetracked with the various forms you see online. For typical screening and treatment, 25(OH)D is the one.

Not medical advice, just a practical next step map.

Step 1: Do not panic, do not guess, just plan testing

If you are moderate to high risk, especially with symptoms, the best move is to test. That gives you a baseline and prevents the endless cycle of supplement roulette.

If you cannot access labs easily, then at least discuss it with a clinician or pharmacist. Especially if you are pregnant, older, have neurologic symptoms, or have conditions like kidney disease.

Step 2: Fix the obvious input problems (without getting extreme)

For B12, if you eat little to no animal foods, you usually need either:

• regular fortified foods you actually eat consistently, or
• a B12 supplement.

For vitamin D, if you get minimal sun and do not eat vitamin D rich foods, you may need:

• supplementation, and or
• intentional sun exposure in a safe way, depending on skin type and skin cancer risk.

But again, the dose question is where testing helps.

Step 3: Look for absorption blockers

If you are on metformin or long term acid reducers, or you have GI issues, you may need monitoring. Sometimes you can do everything “right” and still run low because the pipeline is broken, not the intake.

That is not a moral failing. It is just physiology.

If you have any of these, do not treat this like a casual wellness project.

• Numbness, tingling, burning sensations, or weakness that is worsening
• Balance problems or frequent falls
• Confusion, severe brain fog, personality changes
• Severe bone pain or muscle weakness
• Symptoms of severe anemia like chest pain, fainting, or extreme shortness of breath

Get medical help. Not later.

“I eat healthy, so I cannot be deficient”

You can eat a very clean diet and still have B12 deficiency if you are not eating animal foods or you are not absorbing it.

Same for vitamin D. You can eat perfectly and still be low if you get little sun and do not supplement. Vitamin D production relies heavily on sun exposure, so dietary intake alone may not suffice.

“I am outside sometimes, so my vitamin D is fine”

If you are outside early morning, late afternoon, fully covered, or always in the shade, you might not make much vitamin D. Season and latitude also change the math a lot.

“My B12 test was normal, so it cannot be B12”

Serum B12 can be misleading in some cases. That is where MMA and homocysteine can matter, plus the clinical picture.

“I will just take a huge dose and see if I feel better”

This is how people miss real diagnoses, or overshoot vitamin D over time, or ignore the reason they were low in the first place. Supplements are tools, not shortcuts.

If you want the shortest possible takeaway, here.

You are at higher risk for B12 deficiency if you:

• are vegan or vegetarian without consistent B12 intake
• are over 50
• have GI disease or had bariatric surgery
• take metformin
• take long term acid reducers
• have tingling, numbness, balance issues, or unexplained anemia

You are at higher risk for vitamin D deficiency if you:

• live in a low sun region, especially in winter
• work indoors and rarely get midday sun
• have darker skin and low sun exposure
• have obesity, osteoporosis, kidney or liver issues, or malabsorption
• have frequent infections, muscle aches, bone pain, fatigue, low mood

If you checked a bunch of boxes in either list, get labs. If you checked a bunch in both, test both. It is honestly the fastest way to stop guessing.

One last thing (because people always ask)

Yes, you can be low even if you are young. Yes, symptoms can be subtle. And yes, you can feel “kind of fine” until you suddenly do not.

A simple blood test plus a basic plan can save you months of dragging yourself through the day.

If you want, tell me your age range, diet style (omnivore, vegetarian, vegan), where you live (roughly, like northern US or UK), and your top 3 symptoms. I can help you interpret the checklist score and figure out what to ask for at your next appointment.

FAQs (Frequently Asked Questions)

What are the common symptoms of vitamin B12 deficiency?

Vitamin B12 deficiency often presents with fatigue, weakness, numbness or tingling in hands and feet, brain fog, balance issues, and sometimes mood changes. These symptoms arise because B12 supports red blood cell production, DNA synthesis, and nerve function.

How does vitamin D deficiency affect the body?

Vitamin D deficiency can cause fatigue, low mood, frequent illness, muscle aches, bone pain, and a general feeling of being “off.” Vitamin D acts like a hormone influencing bone health, muscle function, immune regulation, and inflammation.

Who is at higher risk for vitamin B12 deficiency?

Higher risk groups include vegans or mostly vegan individuals (2 points), vegetarians with low dairy or egg intake (1 point), those rarely eating animal foods (1 point), pregnant or breastfeeding women (1 point), people over 50 years old (1 point), individuals with chronic digestive issues or diagnosed gastrointestinal diseases like celiac or Crohn’s (up to 2 points), those who have had bariatric or stomach surgery (2 points), and people taking certain medications such as metformin or acid-reducing drugs.

Can you be deficient in both vitamin B12 and vitamin D at the same time?

Yes, it is possible to be low in both vitamin B12 and vitamin D simultaneously. Their symptoms can overlap significantly, making it difficult to guess which deficiency is present without proper testing.

Should I start taking high doses of supplements if I suspect a deficiency based on symptoms?

No. Symptoms alone are not sufficient for diagnosis. It’s important to get baseline lab tests before starting supplementation, especially for vitamin D since excessive levels can be harmful. Use checklists as risk screeners and consult your healthcare provider for testing.

How can I assess my risk for vitamin B12 deficiency using a checklist?

Assign points based on diet (e.g., vegan = 2 points), gut health conditions (e.g., inflammatory bowel disease = 2 points), medication use (e.g., metformin = 2 points), and symptoms (e.g., tingling in hands/feet = 2 points). Scores of 0-2 indicate lower risk but consider testing if symptoms persist; 3-5 suggest moderate risk where testing is advisable; 6+ indicates high risk where testing is strongly recommended.