Always tired? Vitamin and mineral overlaps to rule out

"I'm always tired" is one of the most common complaints in primary care. Most cases turn out to be lifestyle-driven — sleep debt, chronic stress, poor diet, sedentary patterns — but a handful of vitamin and mineral deficiencies show up often enough that they are worth ruling out early. Here is a practical shortlist of nutrients most commonly associated with persistent fatigue.

The shortlist of fatigue-associated nutrient gaps

1. Iron (ferritin)

Low iron — even without anemia — is the single most common nutrient driver of fatigue, especially in menstruating women, vegetarians, endurance athletes, and frequent blood donors. Ferritin under ~30 ng/mL often warrants repletion even when hemoglobin is normal. Full iron deficiency guide →

2. Vitamin B12

B12 deficiency can cause profound exhaustion, brain fog, and tingling. Risk factors include vegan or long-term vegetarian diets, metformin use, PPI or H2-blocker use, age over 50, and history of bariatric surgery. Serum B12 plus MMA is more sensitive than serum B12 alone. Full B12 deficiency guide →

3. Vitamin D

Vitamin D deficiency is associated with fatigue, low mood, and muscle weakness. It is the most common nutrient deficiency in the US, especially in northern latitudes, indoor workers, and people with darker skin. A simple 25-OH vitamin D test tells you where you stand. Full vitamin D deficiency guide →

4. Magnesium

Low magnesium often shows up as fatigue alongside poor sleep, muscle cramps, restless legs, or anxiety. Heavy sweating, diuretic use, PPI use, and heavy alcohol intake raise risk. Full magnesium deficiency guide →

5. Folate (B9)

Folate deficiency can cause megaloblastic anemia with symptoms similar to B12 deficiency — fatigue, weakness, pallor. Risk factors: alcohol use, malabsorption, methotrexate and other anti-folate drugs, and pregnancy. Folate and B12 are usually tested together because deficiencies can mask one another.

6. Vitamin B6

B6 supports energy metabolism and neurotransmitter synthesis. Severe deficiency is uncommon in well-fed populations but can occur with isoniazid, hydralazine, penicillamine, certain seizure medications, and heavy alcohol use.

Non-nutritional drivers worth checking

• Sleep apnea — fragmented sleep is a massive fatigue driver, often undiagnosed.
• Thyroid — hypothyroidism is a classic cause; TSH with reflex T4 is the starting test.
• Depression — anhedonia and low energy overlap heavily with "just tired."
• Blood sugar — reactive hypoglycemia, prediabetes, or type 2 diabetes.
• Chronic stress — sustained cortisol dysregulation flattens daytime energy.
• Medication side effects — beta blockers, antihistamines, statins, SSRIs, benzodiazepines, opioids.
• Post-viral fatigue — especially after COVID-19, mono, or other viral illness.

Reasonable starter labs

• CBC + ferritin + full iron panel
• Serum B12 + MMA + folate
• 25-hydroxyvitamin D
• TSH with reflex T4
• Fasting glucose + HbA1c
• Magnesium (RBC magnesium is more sensitive than serum)
• Homocysteine (functional marker for B12, folate, B6)

Educational content only. This guide does not diagnose, treat, prescribe, or replace clinician judgment. Persistent or severe fatigue lasting more than a few weeks warrants a conversation with a qualified healthcare professional.