Vitamin D Deficiency: Causes, Symptoms, and What to Do Next

When your body doesn’t get enough vitamin D, a fat-soluble nutrient critical for bone health, immune function, and mood regulation. Also known as the sunshine vitamin, it’s made when your skin is exposed to sunlight—but many people don’t make enough, even in summer. This isn’t just about feeling tired. Low vitamin D links to weaker bones, higher infection risk, and even deeper mood swings—especially in winter months.

It’s not just about skipping the sun. People with darker skin, older adults, those who wear full clothing for cultural or medical reasons, and people living north of 37° latitude are at higher risk. Even if you eat fatty fish or fortified milk, you might still fall short. Your body needs sunlight to convert vitamin D into its active form, and most foods don’t give you enough to meet daily needs. That’s why vitamin D supplements, oral doses used to correct or prevent deficiency are often the only practical solution. But not all supplements are equal—dosage matters, and taking too much can be harmful.

Doctors test for vitamin D levels, the measure of 25-hydroxyvitamin D in your blood, used to diagnose deficiency with a simple blood test. Levels below 20 ng/mL are considered deficient, and many people hover between 20 and 30—still not optimal. Symptoms are quiet at first: fatigue, muscle aches, frequent colds, or feeling down without reason. By the time you feel bone pain, it’s already advanced. The good news? Fixing it usually takes just a few months of consistent, smart dosing.

You’ll find posts here that dig into real-world fixes: how to pick the right supplement, what foods actually help (and what don’t), why some people still stay deficient even with daily pills, and how sunlight exposure timing affects absorption. There are also stories about how low vitamin D ties into other conditions—like immune reactions, sleep issues, and even how it interacts with medications. No fluff. Just what works, what doesn’t, and what you need to know before you buy another bottle.