A patient sat across from me last winter, a little embarrassed. She'd been tired for months, achy in a way she couldn't quite describe, and she kept apologizing for "probably wasting my time." Her labs told a different story. Her vitamin D was low. Really low.
And here's the part that surprised her: she lives in Los Angeles, where the sun shows up almost every day.
I see vitamin D deficiency constantly in my practice, often in people who assume that living in a sunny city makes it impossible. It doesn't. We work indoors, we drive everywhere, and most of us wear sunscreen (which I want you to keep doing). All of that quietly chips away at how much vitamin D your skin actually makes. The good news is that this is one of the easier problems I get to fix.
How do I know if I have a vitamin D deficiency?
You usually can't know from symptoms alone — a simple blood test is the only reliable way to find out. Vitamin D is sneaky. Many people feel completely fine while their levels are low, and others have vague complaints that are easy to blame on a busy life.
When I'm trying to piece things together with a patient, here is what I tend to hear:
- Persistent fatigue that sleep doesn't seem to fix
- Aching bones or muscles, sometimes a dull soreness
- Low mood, especially in the darker months
- Getting sick more often than feels normal
None of these are proof. Plenty of conditions share these symptoms, which is exactly why I'd rather check a level than guess. If your fatigue comes with other clues, I sometimes look further — low iron causing anemia or an underactive thyroid can feel remarkably similar.
Why is vitamin D deficiency so common in Los Angeles?
Because sunshine and skin exposure aren't the same thing. To make vitamin D, your skin needs direct UVB light hitting it — not light through a car window or an office pane. Most of us spend our daylight hours covered up and indoors.
Other things matter too. Darker skin makes vitamin D more slowly. Older skin makes less of it. Carrying extra weight changes how your body stores it. And as we get older, our kidneys and gut become less efficient at putting it to use.
So no, I'm not surprised when a tanned, healthy-looking Angeleno turns out to be deficient. It's one of the most common things I find.
Why does vitamin D actually matter?
Its biggest job is helping your body absorb calcium, which keeps your bones strong. Without enough of it, bones can soften and weaken over time. This is a real concern for anyone worried about osteoporosis and bone health, particularly women after menopause.
But bones aren't the whole story. Vitamin D also supports your immune system and seems to influence mood, muscle strength, and how your body handles blood sugar. I don't promise miracles from a supplement — anyone who does is overselling it. What I will say is that correcting a true deficiency tends to help people feel steadier, and the downside of fixing it is very small.
How is low vitamin D treated?
Most of the time, the fix is straightforward: the right dose of supplemental vitamin D, matched to how low you are and rechecked after a few months. I don't believe in handing everyone the same pill. Someone who's mildly low needs a different plan than someone whose level is in the basement, and the only way to know is to test, treat, and test again.
A few things I talk through with patients:
- Take it with a meal that has some fat — it absorbs far better that way.
- More is not better. Very high doses over long stretches can cause problems, so I'd rather guide the amount than have you self-prescribe.
- Food helps but rarely fixes a real deficiency on its own. Fatty fish and fortified foods are a nice foundation, not a cure.
I usually recheck levels before declaring victory, then we settle into a maintenance dose that keeps you in a healthy range without overshooting. If you want the details on how I approach vitamin D and B12 supplementation, that's where I lay out the plan.
Should I just start taking supplements on my own?
You can, and a modest daily dose is reasonable for many adults — but I'd gently push you to get a level checked first. Guessing means you might take too little to matter or, occasionally, more than you need. A single blood test takes the mystery out of it, and it gives us a real number to track instead of a hunch.
If you've been feeling run-down, achy, or just not quite yourself, this is an easy thing to rule in or out. Reach out and let's talk it through — I'd be glad to check a level, look at the whole picture, and help you feel like yourself again. You're not wasting anyone's time. That's exactly what I'm here for.