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Catching every cold

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

Also described as: colds, sick a lot, always sick, get sick, infections, immune, immunity

Common everyday causes

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.

Low zinc

Zinc runs immune cells, skin repair and hair growth. Plant-based diets, acid reducers and gut conditions lower it. Ask for a plasma zinc test.

Too few fruits and vegetables (vitamin C)

Vitamin C and the polyphenols in produce support immune cells; regular vitamin C shortens colds a little. No test needed.

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).

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 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).

What’s been studied

• Vitamin D3

  For low vitamin D.

• Vitamin K2

  For low vitamin D.

• Zinc

  For low zinc.

• Glycine

  For sleep debt.

• L-theanine

  For sleep debt.

• Rhodiola

  For stress load.

• Magnesium

  For sleep debt.

• Iron

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

• Vitamin C

  For low produce.

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.

• How much vitamin D should you take a day?

  The RDA, the 4,000 IU upper limit, IU vs mcg, D3 vs D2, what a 25-hydroxyvitamin D test means, taking it with a meal, the honest evidence on K2, and who should be careful.

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

Questions

What can cause frequent colds?

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

What tests can help explain frequent colds?

Ask your doctor about: a 25-hydroxy vitamin D test; a plasma zinc test; No test needed; No test. Track sleep for a week; see a doctor if it lasts more than 3 months (CBT-I is first-line); No routine test is reliable (a morning cortisol is only a snapshot); a ferritin test (with a complete blood count).

Which supplements are studied for frequent colds?

Depending on the cause: Vitamin D3, Vitamin K2, Zinc, Glycine, L-theanine, Rhodiola, Magnesium, Iron, Vitamin C. 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.