Vitamin D Deficiency: Causes, Risks, and What to Do About It

When your body doesn’t get enough vitamin D, a fat-soluble nutrient essential for calcium absorption and immune function. Also known as the sunshine vitamin, it’s made when your skin is exposed to sunlight — but many people don’t get enough, even in sunny places. This isn’t just about weak bones. Low vitamin D levels are linked to fatigue, muscle pain, frequent infections, and even mood changes like depression. It’s not rare — studies show over 40% of adults in the U.S. have levels below what’s considered optimal.

Who’s most at risk? People who stay indoors most of the day, wear sunscreen all the time, have dark skin, are over 65, or live far from the equator. Even if you eat fatty fish or fortified milk, it’s often not enough. Your body needs sunlight to make vitamin D, and modern lifestyles make that hard. Some medications — like steroids or weight-loss drugs — can also block how your body uses it. And if you have kidney or liver issues, your body struggles to convert vitamin D into its active form. That’s why checking your levels with a simple blood test is smarter than guessing.

Fixing a deficiency isn’t complicated, but it’s not just about popping a supplement. You need the right dose, the right form (D3 works best), and consistent use over weeks. Too little won’t help. Too much can be harmful. And while sunlight helps, you can’t rely on it alone if you’re in a cold climate or have sensitive skin. That’s why many people end up needing daily supplements — often 1,000 to 4,000 IU — under a doctor’s guidance. It’s also why some of the posts below focus on how vitamin D interacts with other medications, like those for thyroid or kidney conditions, and why monitoring matters.

Below, you’ll find real, practical advice from people who’ve dealt with this — whether it’s how vitamin D affects bone density, why it matters for older adults, or how it interacts with other drugs you might be taking. No fluff. Just what works.