Why You’re Likely Vitamin D Deficient—Especially if You Live Above the 37th Parallel

Introduction

Vitamin D is essential for immune function, bone health, and overall well-being. While we often associate warmer months with higher Vitamin D levels due to increased sunlight, deficiencies remain surprisingly common—especially for those living above the 37th parallel. In this post, we’ll explore why you’re likely deficient, why magnesium is crucial for Vitamin D effectiveness, and how to optimize your Vitamin D levels all year round.

What Is Vitamin D and Why Does It Matter?

While this could be a blog post of its own, here’s a brief overview:

Vitamin D is a fat-soluble vitamin that plays a critical role in supporting immunity, bone health, and mental wellness. Almost every cell in your body depends on Vitamin D, and it’s mostly produced when your skin is exposed to sunlight. However, several factors—including where you live—can limit your body’s ability to produce it.

Why Vitamin D Deficiency Is So Common: The 37th Parallel

Vitamin D deficiency is more widespread than you might think, especially for people living above the 37th parallel (a latitudinal line). Here’s why:

• Limited Sunlight in Winter: Regions above the 37th parallel (think: if you live north of the line that connects San Francisco, CA to Richmond, VA) experience significantly reduced UVB rays in the winter months, which makes it much harder—if not impossible—to synthesize Vitamin D from the sun.

• Reduced UVB Exposure: In the fall and winter months (October to March) UVB rays are largely too weak in these regions to stimulate Vitamin D production effectively. This means you might only get enough Vitamin D in the spring and summer months.

Other Factors that Impact Vitamin D Status

• Indoor Lifestyles: Many of us spend a lotttttttttttt of time indoors, especially compared to our ancestors. Whether we’re working from home or binge-watching our favorite shows (mine currently: The White Lotus), we often miss out on the sun exposure our bodies need to produce Vitamin D.

• Sunscreen Use: Sunscreen is essential for skin protection, but it can block UVB rays—the very rays needed for Vitamin D production. To strike the right balance, try waiting until after you’ve achieved a “pinking dose” (more on that below) before applying sunscreen. That way, you’ll get the benefits of both good Vitamin D status and minimized sun damage.

• Dietary Gaps: Very few foods are rich in Vitamin D, which makes it darn near impossible to get enough from food alone!

Magnesium's Key Role in Vitamin D Metabolism

Many people don’t realize that magnesium is essential for the activation of Vitamin D. Here’s why magnesium is crucial:

• Activation of Vitamin D: Magnesium is required by the enzymes that activate Vitamin D into the form that your body uses, making magnesium an essential cofactor to this conversion.

• Magnesium Deficiency: Many people are magnesium-deficient, either due to poor dietary intake or absorption issues. This magnesium deficiency can worsen Vitamin D deficiency.

What Can You Do About It? Steps to Optimize Your Vitamin D

If you live above the 37th parallel, here’s how to ensure you’re getting enough Vitamin D:

• Get Tested: The best way to find out if you’re deficient is to get your serum 25(OH)D levels tested. Aim for a level of 45-55 ng/mL for optimal health.

• Maximize Sun Exposure in Warmer Months:

  • Aim for 10-30 minutes of midday sun exposure in spring and summer to get the most out of it.

  • Strive for a pink dose– the amount of sun exposure that triggers Vitamin D production without causing skin damage. It’s called the pinking dose because your skin gets a slight pink tint just before it burns. Once achieved, then obviously protect yourself with shade, sunscreen, etc.!

• Optimize Your Diet: Eat more Vitamin D-rich foods (like fatty fish, egg yolks, and liver) and magnesium-rich foods (like leafy greens, nuts, and seeds) to support your body’s overall health.

• Supplement Vitamin D: During winter months or if sun exposure is limited, Vitamin D3 supplementation can help maintain healthy levels. Be sure to check with a healthcare provider before starting any supplementation, and first understand your levels before blindly supplementing!

• Root Cause Exploration: A deficiency in Vitamin D or magnesium may indicate underlying health issues, such as poor gut health or chronic inflammation. Addressing these root causes can help restore balance—and I can help guide you through that! (Book a call) with me if you’re ready to take the next step.

Conclusion

Vitamin D is crucial for your health, but if you live above the 37th parallel, you may be at higher risk for deficiency due to limited sunlight exposure—especially in winter. By getting tested, maximizing your sun exposure in the warmer months, supplementing with Vitamin D when needed, and optimizing your diet with vitamin D and magnesium-rich foods, you can maintain healthy Vitamin D levels year-round. Let’s work together to keep you feeling your best all year long!