Are You Low on Vitamin D? Why It Matters More Than You Think

ByBob Burns

Updated April 02, 2025

Wait—Why Is Vitamin D So Important?

You’ve probably heard it called the “sunshine vitamin,” but vitamin D is technically more like a hormone than a traditional vitamin. It helps your body absorb calcium, keeps your bones and muscles working right, and supports your immune system.

Your body makes it naturally when your skin is exposed to UVB rays from sunlight. But the amount you actually produce depends on a bunch of things—like how much skin is exposed, where you live, the time of year, your skin tone, and your age.

Here’s where it gets tricky: you can feel fine and still be deficient.

Common Signs You Might Be Low

Vitamin D deficiency doesn’t always scream for attention. Sometimes it whispers. Here are a few signs that might raise a red flag:

• Feeling tired all the time, even after a full night’s sleep
  
• Achy bones or muscle weakness
  
• Getting sick more often than usual
  
• Mood swings or feeling down, especially in winter
  
• Hair thinning or loss
  
• Slow wound healing

Of course, those can point to lots of things—but if more than one of these sounds familiar, it’s worth asking about your D levels.

Who’s Most at Risk?

Anyone can be low, but some groups are more likely to struggle with deficiency. This includes:

• Adults over 50 (your skin gets less efficient at producing vitamin D)
• People with darker skin (melanin reduces D production)
• Folks who work indoors or live in northern climates
• People with digestive conditions like Crohn’s or celiac disease
• Those who are overweight or have kidney issues
• Breastfed infants (they usually need a supplement)

Also worth noting: if you always use sunscreen or cover up for skin protection (which is smart!), your D levels may take a hit too.

Best Time for Vitamin D Production

This graph shows UVB intensity over the course of the day, with peak Vitamin D synthesis typically between 10:00 AM and 2:00 PM.

How Is Deficiency Diagnosed?

It’s a simple blood test called the 25-hydroxy vitamin D test. Levels are usually measured in nanograms per milliliter (ng/mL). Most experts agree that:

• Below 20 ng/mL = deficient
  
• 20–30 ng/mL = insufficient
  
• 30–50 ng/mL = ideal for most people

That said, there’s still debate among doctors about what levels are truly optimal—and how much supplementation is safe long-term.

Pro tip: Don’t self-diagnose. Always get tested before starting high-dose supplements.

What Can You Do About It?

If your levels are low, there are a few ways to get back on track:

• Sunlight: Aim for 10–30 minutes of sun exposure a few times per week, depending on your skin tone.
• Supplements: D3 is typically better absorbed than D2. Dosage depends on your blood levels—don’t just guess.
  Diet: Add fatty fish (like salmon), fortified dairy, mushrooms, or egg yolks. But food alone usually isn’t enough.
• Lifestyle: Get outside more if you can, especially in spring and summer.

Just a heads up: over-supplementing can backfire. Too much vitamin D can lead to high calcium levels, which can cause kidney problems. Always check with a healthcare provider for personalized guidance.

Helpful sources:

• NIH Vitamin D Fact Sheet
• Mayo Clinic: Vitamin D Deficiency
• Cleveland Clinic: Signs of Low Vitamin D

A Final Thought

Vitamin D might not be the first thing you think of when you’re feeling off—but maybe it should be. Because when your levels are low, your body feels it in ways you might not expect.

Whether you’re dealing with low energy, winter blues, or just want to support your bones and immune system as you age, it’s worth taking a closer look. A simple test could make a big difference.