Micronutrients: Am I Deficient? How to Test and What to Do About It

You've read the list. Fatigue, brain fog, hair that seems thinner, nails that chip more than they used to. You're left wondering — is this actually a deficiency, or is this just what being tired and busy feels like? Here's how to actually find out, instead of guessing.

How to find out

The most reliable way is bloodwork — but here's the part most people don't know: most providers don't test vitamin and mineral levels proactively unless symptoms specifically point that direction.¹ That means the first step is often just asking. At a routine visit, you can specifically request:

• Vitamin D (25-OH D)

• Vitamin B12

• Ferritin (your iron stores — more accurate than a basic iron test)

• Magnesium

One nuance worth knowing before you ask

Standard magnesium tests measure serum magnesium — but only about 1% of your body's total magnesium actually lives in your blood serum. The rest sits inside your cells.² That means a "normal" serum result can still miss a real, meaningful deficiency happening at the cellular level. If magnesium is a concern for you, ask specifically for an RBC (red blood cell) magnesium test instead — it reflects what's actually stored in your cells, and it catches shortfalls the standard test misses.²

If you'd rather not wait for a doctor's visit, direct-to-consumer test kits (through labs like Quest or LabCorp's consumer platforms) are available too. They're a reasonable starting point, though having a doctor interpret your results alongside your actual symptoms and history tends to be more useful than a number sitting on its own.

What to do if you're actually low

Once you have real numbers instead of a guess, there's a clear order of operations:

1. Food first, for anything mild. Whole foods bring fiber and cofactors along with the nutrient itself — something a pill can't fully replicate.

2. Targeted supplementation for anything moderate to significant — dosed to your actual result, not a guess, and ideally checked against any medications you're taking.

3. Retest in a few months. This is the step almost everyone skips. Without retesting, you're hoping it worked instead of actually knowing.

The holistic piece: how you eat matters as much as what you eat

This part is genuinely useful and often overlooked entirely:

• Iron + vitamin C: pairing plant-based iron (spinach, lentils) with vitamin C (citrus, tomatoes) can boost absorption dramatically — from as little as 2% up to 65% in some research.³

• Fat-soluble vitamins (A, D, E, K) + a source of fat: a salad with olive oil absorbs its nutrients far better than the same salad eaten dry.⁴

• Calcium + vitamin D together: think salmon paired with leafy greens, rather than either on its own.⁴

What quietly drains your stores, regardless of how well you eat

A few things work against you in the background, no matter how good your diet looks on paper: chronic stress (especially magnesium), alcohol (B vitamins, magnesium, zinc), poor sleep, and certain medications like diuretics or acid blockers.⁵ Addressing those isn't a separate project from fixing a deficiency — it's part of the same one. You can eat perfectly and still run low if one of these is quietly working against you.

Here's what to actually do

You don't need every test or every fix at once. Start with the symptom that's actually bothering you most, ask for the specific test connected to it, and let a real number — not a guess — decide your next step. If the result comes back low, follow the food-first-then-targeted-supplement order above, and put a retest on the calendar so you actually know it worked.

This article is for educational purposes and isn't a substitute for personalized medical advice. Please talk with your doctor about which tests and next steps make sense for your specific symptoms and history.

Sources

1. Provider testing practices for vitamin and mineral panels: How to interpret blood tests for 7 common vitamin deficiencies — Levels

2. RBC magnesium vs. serum magnesium accuracy: Magnesium Levels and the Difference between Serum and RBC Blood Tests — Xandro Lab

3. Iron and vitamin C absorption pairing: Top Food Combos to Maximize Nutrient Absorption

4. Fat-soluble vitamin and calcium/vitamin D pairing: 7 Food Pairings to Increase Nutrient Absorption — Health Spectra

5. Stress, alcohol, sleep, and medication as nutrient depleters: The Great Nutrient Heist: How Alcohol Steals Your Body's Essential Vitamins and Minerals; stress-specific findings via Nutrients Depleted When You Are Stressed