Vitamin D Deficiency: 9 Signs You’re Low — and Why Half of America Doesn’t Know It

Vitamin D deficiency affects an estimated 41% of American adults. Most don’t know they have it. Here are the signs to watch for.

Why Are So Many People Deficient?

Your body makes vitamin D from sunlight — but modern indoor lifestyles, sunscreen use, and limited sun exposure in northern states mean millions are running chronically low. Dark skin, obesity, and older age also reduce vitamin D production.

9 Signs You May Be Deficient

1. Fatigue and tiredness — even with adequate sleep
2. Bone pain and aching — vitamin D is essential for calcium absorption
3. Muscle weakness
4. Frequent illness — vitamin D supports immune function
5. Depression or low mood — D affects serotonin production
6. Hair loss — linked to severe deficiency
7. Back pain
8. Slow wound healing
9. Brain fog and poor concentration

How to Know for Sure

Ask your doctor for a 25-hydroxyvitamin D blood test. Normal is 20–50 ng/mL. Deficiency is below 20 ng/mL. Supplementing 2,000–4,000 IU daily is generally safe for most adults, but get tested before taking high doses.

📌 Source: NIH, Cleveland Clinic. Consult your doctor before starting supplements.