Home / Symptoms

SYMPTOMS

Tired or low energy

Everyday reasons for tiredness, what to ask your doctor to check, and which nutrients have been studied.

Also described as: tired, tiredness, fatigue, fatigued, exhausted, exhaustion, no energy, low energy, worn out, drained, lethargic, sluggish

Common everyday causes

Not enough restorative sleep

Under 7 hours, or broken sleep, lowers energy, focus, mood and immune defenses and raises cravings the next day. No test. Track sleep for a week; see a doctor if it lasts more than 3 months (CBT-I is first-line).

Low iron stores

Iron carries oxygen and powers energy production; stores (ferritin) run low well before anemia shows, especially with heavy periods or a plant-based diet. Ask for a ferritin test (with a complete blood count).

Low vitamin D

Vitamin D supports muscles, bones, mood and immune defenses. Low levels are very common, especially in winter, with darker skin or little sun. Ask for a 25-hydroxy vitamin D test.

Cellular energy (mitochondria) running low

Mitochondria turn food into energy. Age, statins, chronic stress and illness slow them; CoQ10, carnitine and riboflavin feed them. No routine test. This is the layer to try when the first ones are addressed or ruled out.

Stress load (your stress response on overdrive)

Ongoing stress keeps cortisol and adrenaline up: wired-but-tired, poor sleep, cravings, gut upset, shedding and lower libido. No routine test is reliable (a morning cortisol is only a snapshot).

Low vitamin B12

B12 keeps nerves and red blood cells healthy; low levels cause tiredness, brain fog and tingling. Common with metformin, acid reducers, a plant-based diet and after weight-loss surgery. Ask for a vitamin B12 test (and methylmalonic acid if it’s borderline).

If you take certain medicines

Metformin lowering B12

Metformin reduces B12 absorption; about 1 in 10 long-term users become deficient. Ask for a B12 test — the ADA advises checking it regularly on metformin.

GLP-1 medicine: eating less protein and nutrients

GLP-1 medicines cut appetite so much that protein and micronutrients often fall short; fast weight loss also triggers hair shedding. Ask for B12, ferritin and vitamin D tests; aim for 25–30 g of protein per meal.

Statin lowering CoQ10

Statins block the same pathway the body uses to make CoQ10, an energy molecule in muscle cells. Muscle aches and tiredness are the most common statin complaints. Tell your prescriber about muscle symptoms; they may check CK. There’s no routine CoQ10 test.

Acid reducer lowering magnesium and B12

Long-term acid reducers (especially PPIs) lower magnesium and B12 absorption. Ask for magnesium and B12 tests, and whether you still need the acid reducer.

What’s been studied

• Glycine

  For sleep debt.

• Iron

  For low iron. Only with a lab result that shows it’s needed.

• Vitamin C

  For low iron. Only with a lab result that shows it’s needed.

• Vitamin D3

  For low vitamin D.

• Vitamin K2

  For low vitamin D.

• Acetyl-L-carnitine

  For cellular energy.

• Vitamin B2

  For cellular energy.

• L-theanine

  For sleep debt.

• Rhodiola

  For stress load.

• Magnesium

  For GLP-1 medicine.

From the Journal

• Are personalized vitamins worth it? Personalized blend vs a multivitamin

  What a standard multivitamin does well, where it falls short, what research says about personalized nutrition, and how to tell whether a personalized blend makes sense for you.

• Iron and ferritin: who actually needs an iron supplement?

  What ferritin and transferrin saturation show, who tends to run low on iron, why to test before taking it, hemochromatosis caution, and how to take iron so it absorbs and sits well.

• How much creatine should you take a day, and is it safe?

  Creatine dosing made simple: 3 g vs 5 g a day, why loading is optional, what the brain research does and doesn't show, the creatinine lab quirk, and who should check first.

• Folic acid vs methylfolate: does your MTHFR gene matter?

  How folic acid and L-methylfolate differ, what an MTHFR variant does and doesn't mean, what the pregnancy guidance actually says, and the upper limit for folic acid.

• Which blood tests should you check before taking supplements?

  The blood tests that can usefully guide supplements, what each one can and can't tell you, and when to recheck after you change what you take.

• How many supplement pills a day is too many?

  Why adherence drops as daily doses and pill counts rise, how separate bottles double up on the same nutrients and push past upper limits, and how to simplify a supplement routine safely.

apiece asks a few quick questions about tiredness in its quiz to tell these causes apart, and suggests only ingredients studied for the likely ones.

Questions

What can cause tiredness?

Common everyday reasons include sleep debt, low iron, low vitamin D, cellular energy, stress load. A doctor can help find which applies to you.

What tests can help explain tiredness?

Ask your doctor about: No test. Track sleep for a week; see a doctor if it lasts more than 3 months (CBT-I is first-line); a ferritin test (with a complete blood count); a 25-hydroxy vitamin D test; No routine test. This is the layer to try when the first ones are addressed or ruled out; No routine test is reliable (a morning cortisol is only a snapshot); a vitamin B12 test (and methylmalonic acid if it’s borderline).

Which supplements are studied for tiredness?

Depending on the cause: Glycine, Iron, Vitamin C, Vitamin D3, Vitamin K2, Acetyl-L-carnitine, Vitamin B2, L-theanine, Rhodiola, Magnesium. Some only make sense with a lab result (for example iron only when ferritin is low).*

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This page is general information, not medical advice. Check with your doctor or pharmacist before starting a supplement, especially if you take medication, are pregnant or nursing, or have a health condition. Updated 2026-10-21.