Nutrient Panel: Vitamin D, B12, Iron, Folate, and Magnesium Testing

Quick answer

The most useful nutrient blood tests are vitamin D, vitamin B12, folate, ferritin, and magnesium. Ferritin is the best marker for the iron stored in your body. In the Philippines, low vitamin D, low B12, and low ferritin are the most common problems, and people with these deficiencies often feel healthy otherwise.

Vitamin D (25-OH)

What it measures: a stored form of the vitamin called 25-hydroxyvitamin D, or 25-OH for short. Think of it as your body's vitamin D savings account.

The lab's normal range: above 20 ng/mL. The healthy target range: 40 to 60 ng/mL.

Why it matters:

• Helps your body use calcium to build strong bones.
• Supports your immune system.
• Affects mood. Low levels are linked to feeling low.
• Helps your body respond to insulin.
• Supports a healthy heart.

Why so many Filipinos run low, even with sun all year:

• Office hours keep people indoors during peak sun hours.
• Sunscreen and covered clothing block the sun your skin needs.
• Air pollution cuts down how much sunlight reaches your skin.
• Darker skin needs more sun time to make the same amount of vitamin D.

What to do based on your level:

• Below 20 ng/mL (low): take 4,000 to 5,000 IU a day for 12 weeks, then retest.
• 20 to 29 ng/mL (a bit low): take 2,000 to 3,000 IU a day for 12 weeks.
• 30 to 39 ng/mL (borderline): take 1,000 to 2,000 IU a day, plus more sun.
• 40 to 60 ng/mL: this is the healthy target range.
• 60 to 100 ng/mL: high, but still safe.
• Above 100 ng/mL: cut back on your dose.

Vitamin B12

What it measures: cobalamin, a vitamin your body needs for energy and healthy nerves.

The lab's normal range: above 200 pg/mL. The healthy target range: 500 to 900 pg/mL.

Why it matters:

• Powers your energy.
• Helps your body build new red blood cells. Low B12 can cause a type of anemia.
• Keeps your nerves working right. Low B12 can cause tingling or numbness.
• Supports mood and clear thinking.
• Works as a team with folate.

Who runs the highest risk:

• People who eat mostly plant foods, since B12 comes mainly from animal foods.
• Adults over 50, because the body absorbs less B12 with age.
• People on long-term heartburn medicine or the diabetes drug metformin.
• People with gut conditions that block absorption.

What to do based on your level:

• Below 200 (low): take 1,000 mcg of methylcobalamin a day, and find out why.
• 200 to 499 (borderline): take 500 to 1,000 mcg a day.
• 500 to 900: this is the healthy target range.
• Above 900: usually from supplements, and not harmful.

A result of 250 clears the lab's cutoff, but it still sits far below the target. Here is why the bottom of the B12 range is a problem for how you feel.

Folate

What it measures: folate, also called vitamin B9.

The lab's normal range: above 5.4 ng/mL. The healthy target range: above 9 ng/mL.

Why it matters:

• Helps build DNA and new red blood cells.
• Critical in early pregnancy for the baby's brain and spine.
• Works as a team with B12.
• Supports mood and clear thinking.

Best tested together with: B12, since fixing one without the other can hide a problem with the other. Also test homocysteine, a marker that often rises when folate or B12 runs low.

Ferritin (iron status)

What it measures: your iron storage marker. It moves up or down before the iron in your blood does. Think of ferritin as your iron savings account, and blood iron as your iron spending money.

The lab's normal range: 11 to 307 ng/mL for women; 24 to 336 ng/mL for men. The healthy target range: 50 to 150 ng/mL.

Why it matters:

• Iron helps your blood carry oxygen around your body.
• Low ferritin causes fatigue, hair loss, poor exercise tolerance, and thyroid problems, often before anemia shows up on a standard blood count.
• Very common in women who have periods, people who eat mostly plants, and women with heavy periods.

An important note: ferritin also rises when your body is inflamed. A high ferritin with low iron saturation usually points to inflammation, not too much iron. Ask your doctor to check it alongside hs-CRP, an inflammation marker, and serum iron.

What to do based on your level:

• Below 30 (low): find out why, consider iron, and ask about a gut check if there is no clear cause.
• 30 to 49 (low normal): eat more iron-rich foods, or take a supplement.
• 50 to 150: this is the healthy target range.
• Above 150: ask your doctor to check for inflammation or too much iron.

Magnesium

What it measures: magnesium in your blood. Some doctors test magnesium inside your red blood cells instead, since it gives a clearer picture.

The lab's normal range: 1.7 to 2.2 mg/dL. The healthy target range: the higher end of the normal range.

Why it matters:

• Helps run more than 300 chemical reactions in your body.
• Keeps muscles and nerves working right. Low levels can cause cramps or restless legs.
• Helps you sleep.
• Helps your body use sugar and insulin.
• Keeps your heartbeat steady.

Why testing is tricky: your blood magnesium level does not always match what is stored in your cells. Your body protects blood levels first, even when cell stores run low. A red blood cell magnesium test is more accurate, but fewer labs offer it.

Common reasons Filipinos run low:

• Diets heavy in white rice instead of whole grains.
• Not enough leafy greens, nuts, and seeds.
• Too much caffeine or alcohol.
• Water pills, also called diuretics.
• Diabetes.

Zinc

What it measures: zinc in your blood.

The lab's normal range: 70 to 150 mcg/dL.

Why it matters: zinc supports your immune system, wound healing, taste, smell, reproductive hormones, and how your thyroid works.

Signs of low zinc: frequent colds, slow-healing cuts, hair loss, low interest in sex, and wounds that will not close.

Less common tests worth knowing about

• Iodine. Your thyroid needs iodine to make its hormones. Iodized salt covers most people, so deficiency is rare where salt is iodized.
• Vitamins A, E, and K. Doctors usually only test these when they suspect a specific problem.
• Selenium. Supports your thyroid and fights cell damage. Brazil nuts are the richest food source.
• Copper. Rarely low on a normal diet. More often runs high when the body is inflamed.
• Vitamin C. Usually fine on a normal diet. Testable if your doctor has a specific reason.

See the full &you Labs biomarker list for everything a comprehensive panel can cover.

Common patterns

Pattern 1: The classic combination

• Vitamin D under 30 ng/mL.
• B12 borderline low.
• Ferritin under 50 ng/mL.
• Often comes with fatigue, brain fog, and hair concerns.

This combination shows up often in Filipino adults, and all three parts are easy to fix.

Pattern 2: A methylation problem

• High homocysteine.
• Borderline folate or B12.
• Sometimes low active B6.
• What to do: take a B-vitamin combination, then retest in 12 weeks.

Pattern 3: Inflammation hiding low iron

• Low iron in the blood.
• Low iron saturation.
• Normal or high ferritin.
• High hs-CRP.
• What to do: treat the inflammation, not the iron.

Pattern 4: Hidden iron deficiency

• Hemoglobin still normal.
• MCV, a red blood cell size marker, at the low end of normal.
• Ferritin under 30 ng/mL.
• Symptoms like fatigue, hair loss, and poor exercise tolerance.
• What to do: take iron, and find out why.

When to test

• Every year: vitamin D, B12, folate, and ferritin for every adult.
• When symptoms show up: magnesium, zinc, and other markers.
• Planning a pregnancy or pregnant: a full nutrient panel plus iodine.
• Eating mostly plants: B12 and ferritin at least once a year.
• Heavy periods: ferritin every 6 months.
• After starting a supplement: retest at 12 weeks to confirm it worked.

If you want all five of these checked in one visit, a &you Labs panel covers them together, with a doctor's interpretation included.

Frequently asked questions

Should I take vitamin D without testing first?

For most adults, a daily dose of 1,000 to 2,000 IU is safe without testing. Low vitamin D is common, and this dose is low risk. For a higher dose, or to fix a real deficiency, test first so you can track your progress.

How long does it take to fix a deficiency?

Vitamin D takes about 12 weeks at treatment doses. B12 takes 6 to 12 weeks. Iron takes 12 weeks or more, since it refills slowly. Folate takes 4 to 8 weeks. Magnesium varies. Always retest after this window to confirm it worked.

Do foods work as well as supplements?

For most nutrients, yes, and often better. Food gives your body helper nutrients that a pill cannot. Supplements make the most sense when you have a real deficiency, follow a diet that skips certain foods, or cannot eat enough of a nutrient through food alone.

Are there nutrient tests I should skip?

Hair mineral tests, food sensitivity panels based on IgG, and most "metabolic typing" tests have weak evidence and often give misleading results. Stick to standard blood tests that are well studied.

Can I get all of these from one blood draw?

Yes. All five nutrients fit into one standard blood draw, along with the rest of a full panel.

Key takeaways

• Low nutrient levels are common, even for people who eat well and get sun.
• The five most useful nutrient tests are vitamin D, B12, folate, ferritin, and magnesium.
• Low vitamin D, borderline B12, and low ferritin often show up together, and all three are easy to fix.
• Ferritin is the best marker for iron levels. Check it alongside an inflammation marker for the full picture.
• Retest 12 weeks after starting a supplement to confirm it worked.