Vitamin D—Why You Need More Than You Think

When you think about vitamin D, chances are you picture strong bones and calcium. And while that’s true, it’s just the tip of the iceberg.

Vitamin D is not just a vitamin—it functions more like a hormone, influencing hundreds of processes in your body. From your immune system to your metabolism, mood, and long-term disease risk, vitamin D plays a role in nearly everything.

And here’s the reality: most people in North America are not getting enough.

In this post, we’ll dive deep into why vitamin D is so important, what the latest research shows, and how you can make sure your levels are truly optimal.

Why Vitamin D Is So Important

Yes, vitamin D helps your body absorb calcium and phosphorus, which are critical for strong bones. But its role goes far beyond bone health.

🛡️ Immune Function and COVID Outcomes

During the COVID-19 pandemic, study after study found the same striking pattern:

• People with low vitamin D levels had worse outcomes—higher hospitalization, more ICU admissions, and higher death rates.
  
  
• People with sufficient or higher vitamin D levels had better outcomes, recovering faster and avoiding severe complications.
  
  

That’s because vitamin D doesn’t just support your immune system—it regulates it. It helps your immune cells fight effectively while also preventing the dangerous overreactions (like cytokine storms) that can cause serious harm.

🔥 Metabolic and Inflammatory Health

Vitamin D supports insulin sensitivity, lowering the risk of insulin resistance, diabetes, and metabolic syndrome. It also reduces chronic inflammation—the silent driver behind heart disease, obesity, autoimmunity, and cancer.

🧠 Mood, Cognition, and Energy

Low vitamin D is strongly linked with depression, fatigue, seasonal affective disorder, and even cognitive decline. That “winter blues” feeling? Low vitamin D is often part of the story.

💪 Muscle Strength and Performance

Vitamin D keeps your muscles firing properly. Deficiency shows up as weakness, slower recovery, and greater fall risk. Athletes with low vitamin D often notice slower healing and reduced performance.

How Your Body Gets Vitamin D

☀️ Sunlight

Your body is designed to make vitamin D from the sun. When UVB rays hit your skin, they trigger vitamin D production that’s then activated in the liver and kidneys.

But here’s the catch:

• UVB is only strong enough between 10 a.m. and 3 p.m.
  
  
• Above the 37th parallel—think San Francisco to Richmond, VA—the sun is too weak in fall and winter to make vitamin D.
  
  
• Darker skin, older age, and higher body fat all reduce vitamin D production.
  
  

🥑 Food Sources

Food helps, but it’s not enough on its own. The best sources are:

• Fatty fish like salmon and sardines (wild caught)
  
  
• Cod liver oil
  
  
• Egg yolks and beef liver
  
  
• Mushrooms exposed to UV light
  
  

But unless you’re eating fish daily, food alone won’t get you to optimal levels.

💊 Supplements: Why D3 + K2 Matters

When it comes to supplements, D3 is the form you want—it’s what your body naturally makes from sunlight. D2, the plant-derived form, is weaker and less effective.

But here’s something many people don’t know: vitamin D increases calcium absorption. Without enough vitamin K2, that calcium can end up in your arteries and soft tissues instead of your bones. K2 acts like a traffic cop, directing calcium to the right place.

Magnesium is also critical. It’s a cofactor for the enzymes that activate vitamin D. Without it, your body can’t fully use the vitamin D you’re getting.

The Deficiency Problem in North America

Deficiency is widespread:

• In the U.S., around 40% of adults are insufficient (20–29 ng/mL), and 20–25% are outright deficient (<20 ng/mL).
  
  
• In Canada, about 37% of people are deficient by the same measure.
  
  
• Among Black Americans, deficiency rates are as high as 73%, because melanin blocks UVB rays.
  
  

In other words: low vitamin D is not rare—it’s the norm.

Myths About Vitamin D

Let’s clear up a few common misconceptions:

• “Any sun makes vitamin D.” False—only UVB counts, and it has to be midday.
  
  
• “A tan protects you.” Actually, it means slower vitamin D production.
  
  
• “Sunscreen blocks it completely.” In theory yes, but most people don’t apply enough. Still, heavy sunscreen lowers vitamin D status.
  
  
• “Showering washes it off.” Not true—vitamin D is made inside your skin cells.
  
  
• “Food is enough.” Realistically, no.
  
  
• “More is better.” Too much vitamin D can cause calcium buildup in arteries and kidneys. Balance matters.
  
  

What’s the Ideal Vitamin D Level?

Here’s where conventional medicine and functional medicine differ:

• Conventional ranges:
  
  
• Deficient: <20 ng/mL (50 nmol/L)
  
  
• Insufficient: 20–29 ng/mL (50–75 nmol/L)
  
  
• Sufficient: 30+ ng/mL (75+ nmol/L)
  
  
• Functional medicine ranges:
  
  
• Optimal: 50–80 ng/mL (125–200 nmol/L)
  
  
• Why? Because research shows improved immunity, mood, metabolism, and reduced chronic disease risk at these higher levels.
  
  

In other words, conventional ranges aim to prevent rickets. Functional ranges aim to help you thrive.

How to Test Your Vitamin D

The best way to know your status is a blood test for 25-hydroxy vitamin D.

If you don’t want to go into a lab, I also offer an at-home vitamin D finger-prick test kit. It’s quick, simple, and gives you an accurate result so you can supplement strategically instead of guessing. Use code 104567 to create an account.

The Bottom Line

Vitamin D is essential for so much more than bone health. It influences your immune system, metabolism, mood, energy, and long-term health risks.

Most people in North America are insufficient or deficient. Sunlight helps—but only in the right conditions. Food plays a small role, but rarely enough. For most people, supplements—D3 with K2, plus magnesium support—are the missing piece.

Don’t guess. Test your levels, know your number, and aim for that functional sweet spot of 50–80 ng/mL. Your health is worth it.

👉 Ready to stop guessing? Click here to get your at-home vitamin D finger-prick kit. Use code 104567 to create an account.

🎧 Want the full conversation? Listen to the Lifestyle School podcast episode: Vitamin D—Why You Need More Than You Think.

➡️ Click here to listen now on Apple Podcasts or Spotify
(Or search Lifestyle School with Hope Plack on your favorite podcast app.)