A patient sat across from me last month, exhausted. She'd been buying every vitamin the wellness aisle recommended, swallowing a fistful each morning, and still felt foggy and tired. Sound familiar? I see it constantly. People take supplements as a guess — sometimes the right ones, often the wrong ones, almost never the right amount.
That's the heart of what I want you to know about vitamin D and B12 supplementation: it works best when it's targeted. Not a shotgun. A lab result tells me what your body is actually missing, and then we fix exactly that. Here in Los Angeles, where I'd assume everyone is soaking up sun and feeling great, I find low vitamin D more often than you'd expect.
How do I know if I'm actually deficient in vitamin D or B12?
You find out with a simple blood test — not by guessing from symptoms. That's the part most people skip.
The trouble is that deficiency symptoms are vague and overlapping. Tiredness, low mood, trouble concentrating, achy muscles, weaker bones. Plenty of things cause those, which is why I don't want you self-diagnosing from a website (including this one). A quick draw measures your vitamin D and B12 levels directly, and then we're working with facts instead of hunches.
In my practice, I'll often check these as part of a broader workup when someone comes in dragging. If your numbers are low, we treat them. If they're normal, we keep looking — because chasing a vitamin that isn't the problem just delays the real answer.
Why is vitamin D so common to run low on in sunny LA?
Because sunshine isn't the whole story. Your skin makes vitamin D from sunlight, but most of us spend our days indoors, commuting, working, wearing sunscreen — all good habits that quietly cut down on production.
Age matters too. So does skin tone, certain digestive conditions, and how much fish and fortified food you eat. I've had marathoners and beach regulars come back with low levels and look genuinely surprised.
Vitamin D matters for your bones in particular. It helps your body absorb calcium, which is why I pay close attention to it in patients concerned about bone health and osteoporosis. Correcting a real deficiency is one of the simpler, more rewarding things we do.
What does B12 do, and who tends to run low?
B12 keeps your nerves and red blood cells healthy, and a shortage can leave you tired, foggy, or tingly in the hands and feet.
Some people are more prone to it. A few groups I keep an eye on:
- Vegans and vegetarians, since B12 mostly comes from animal foods
- Older adults, who absorb it less efficiently
- People on certain long-term medications, including some for acid reflux and diabetes
Low B12 can also show up alongside anemia, which is one more reason I'd rather test than assume. The fix might be a pill, or sometimes an injection — but only once we know that's what's actually going on.
Can't I just buy supplements at the store and skip the doctor?
You can buy them, sure — but more isn't better, and a few vitamins can build up to unhealthy levels if you overdo them.
Vitamin D is fat-soluble, meaning your body stores the excess rather than flushing it out. Mega-doses you find online can push levels too high. B12 is gentler, but if your fatigue is coming from something else entirely, no amount of it will help. I'd rather you spend money on what works.
Here's how I usually approach it. We test first. If a level is low, we pick a sensible dose and a timeline. Then we recheck to confirm you've corrected it, and adjust from there. It's not complicated — it's just specific to you.
What about fatigue that supplements don't fix?
Sometimes the vitamins are normal and you're still wiped out, and that's important information, not a dead end.
Thyroid issues, anemia, sleep problems, stress, and other conditions can all mimic a deficiency. When that's the case, I'd rather find the real cause than keep you swallowing pills that aren't moving the needle. Targeted care means knowing when to add a supplement — and when to look elsewhere.
If you've been guessing at your vitamins and not feeling any better, let's take the guesswork out of it. I'm happy to talk through your symptoms, run the right labs, and build a plan that fits you — reach out anytime and we'll get started.