Who is this especially useful for?
- ✓People living in northern latitudes or with limited sun exposure
- ✓Those with darker skin tones (reduced vitamin D synthesis)
- ✓Individuals experiencing fatigue, mood issues, or frequent infections
- ✓Anyone on low-fat diets (vitamin D is fat-soluble)
- ✓People taking medications that deplete vitamin D (statins, corticosteroids, anticonvulsants)
- ✓Older adults (skin synthesis decreases with age)
Vitamin D deficiency is remarkably common — even in sunny climates due to indoor lifestyles and sun avoidance.
Vitamin D is often called a vitamin, but it's actually a steroid hormone that your body produces when sunlight hits your skin. This "sunshine hormone" affects virtually every cell in your body through vitamin D receptors (VDRs) found in tissues from your brain to your bones.
Despite its importance, vitamin D deficiency is epidemic — affecting an estimated 42% of US adults. Modern indoor lifestyles, sun avoidance, and living far from the equator have created widespread insufficiency that many don't recognize until symptoms appear.
How to Test
💡 Pro tip: Test in February or March to see your lowest point of the year. This tells you if your winter sun exposure and supplementation are adequate.
🔍Where to find your result
Some labs report both forms. Focus only on 25-OH-D for assessing your vitamin D status.
What is Vitamin D?
Vitamin D is a fat-soluble secosteroid hormone essential for calcium absorption, bone health, immune function, and cellular processes. Unlike most vitamins, your body can produce it — when UVB rays from sunlight convert cholesterol in your skin to vitamin D3 (cholecalciferol).
Once produced or consumed, vitamin D undergoes two conversions: first in the liver to 25-hydroxyvitamin D (the storage form we measure), then in the kidneys and other tissues to 1,25-dihydroxyvitamin D (the active hormone that binds to vitamin D receptors).
Vitamin D receptors exist in over 30 tissues and regulate more than 200 genes — influencing everything from bone density to immune response to mood regulation. This is why deficiency can manifest in such diverse ways.
The Two Forms of Vitamin D
D3 (Cholecalciferol)
✓ PreferredProduced by skin from sunlight; found in animal foods (fatty fish, egg yolks). More effective at raising blood levels.
D2 (Ergocalciferol)
Found in some mushrooms and fortified foods. Less potent and shorter-acting than D3.
Most experts recommend D3 for supplementation due to better efficacy and longer half-life.
What Research Shows
Large-scale studies consistently show associations between low vitamin D and increased risk of respiratory infections, autoimmune diseases, cardiovascular events, and all-cause mortality. The 2017 Martineau meta-analysis of 25 RCTs found vitamin D supplementation reduced acute respiratory infections by 12% overall, with strongest effects in those starting with deficiency.
11,000+ participants across 25 randomized controlled trials
How Different Paradigms Interpret This
The definition of "optimal" vitamin D varies dramatically between medical approaches:
Vitamin D Interpretation by Paradigm
Each paradigm has different thresholds, focus areas, and recommended actions:
Standard Medical
Research Consensus
Metabolic Optimization
Standard Medical
Endocrine Society and most conventional lab ranges focus on preventing rickets (deficiency < 20 ng/mL) and maintaining basic bone health. Values above 30 ng/mL are considered 'sufficient' with little attention to potential benefits of higher levels.
Supplement only if deficient (< 20 ng/mL) or insufficient (< 30 ng/mL). Standard dose is 600-800 IU daily. Routine testing not recommended for asymptomatic individuals.
Research Consensus
Growing evidence suggests 40-60 ng/mL supports immune function, mood regulation, and disease prevention beyond bone health. The Endocrine Society's sufficiency threshold (30 ng/mL) may be too conservative for optimal health.
Target 50-80 ng/mL for broad health benefits. Consider 2,000-5,000 IU daily depending on baseline levels, body weight, and sun exposure. Retest at 3 months to verify response.
Metabolic Optimization
Emphasizes vitamin D as a hormone affecting 200+ genes and every tissue with VDR receptors. Higher levels (60-100 ng/mL) may optimize immune surveillance, insulin sensitivity, and cellular function — especially important for metabolic health.
Target 60-100 ng/mL with appropriate co-factors (K2-MK7, magnesium). Higher doses (5,000-10,000 IU) may be needed initially. Always include K2 to ensure proper calcium metabolism. Monitor levels quarterly until stable.
Signs of Vitamin D Deficiency
Deficiency often develops slowly and symptoms are non-specific, making it easy to miss:
Fatigue and tiredness
Even with adequate sleep
Bone and back pain
Especially lower back
Depression and mood changes
Particularly in winter (SAD)
Impaired wound healing
Slower recovery from cuts, surgery
Bone loss
Low bone mineral density on DEXA
Hair loss
Especially alopecia areata
Muscle pain and weakness
Chronic aches without explanation
Frequent infections
Getting sick often, slow recovery
These symptoms have many causes. Testing is the only way to confirm vitamin D deficiency.
How to Optimize Your Vitamin D
Multiple strategies can help raise and maintain healthy vitamin D levels:
Sun Exposure
Midday sun is most efficient
10am-2pm when UVB rays are strongest
15-30 minutes on arms/legs
Without sunscreen for D synthesis
Skin tone matters
Darker skin needs 3-5x more exposure
UV index > 3 required
Below this, minimal D is produced
Dietary Sources
Fatty fish
Salmon, mackerel, sardines: 400-1000 IU/serving
Cod liver oil
1,400 IU per teaspoon (plus vitamin A)
Egg yolks (pastured)
40-50 IU each; more if hens had UV exposure
Beef liver
40-50 IU per serving
Supplementation
Choose D3 over D2
Cholecalciferol is more effective
Take with fat
Fat-soluble vitamin needs fat for absorption
Consider K2-MK7 co-factor
Helps direct calcium properly; dosing varies — consult provider
Don't forget magnesium
Required for vitamin D metabolism
Important Co-Factors
Vitamin K2 (MK-7)
Activates proteins that direct calcium to bones (not arteries). Critical at higher D doses.
Dosages discussed in metabolic health communities vary widely. Consider testing undercarboxylated osteocalcin to personalize. Consult your healthcare provider.
Magnesium
Required for converting vitamin D to its active form. Deficiency limits D effectiveness.
Many are deficient. Consider 200-400mg daily of well-absorbed forms (glycinate, malate).
Zinc
Needed for vitamin D receptor function and immune synergy.
15-30mg daily if deficient; balance with copper for long-term use.
Blood levels rise within 2-4 weeks of consistent supplementation. Steady state is reached at approximately 3 months. Symptoms like fatigue and mood often improve within 4-8 weeks of reaching optimal levels. Bone-related benefits take longer — 6-12 months for measurable changes in bone density.
What About Toxicity?
True vitamin D toxicity is rare and requires very high levels (typically > 150 ng/mL sustained) or extremely high supplementation (> 50,000 IU daily for extended periods). Symptoms include hypercalcemia (high blood calcium), nausea, weakness, and kidney issues. At reasonable supplementation levels with proper co-factors, toxicity is very unlikely. However, those taking more than 5,000 IU daily long-term should monitor levels periodically.
Key Takeaways
- 1Test 25-OH-D (not 1,25-OH-D) to accurately assess your vitamin D status
- 2Standard 'sufficient' (30 ng/mL) may be suboptimal; research suggests 50-80 ng/mL for broad health benefits
- 3Metabolic optimization approaches often target 60-100 ng/mL with appropriate co-factors
- 4D3 (cholecalciferol) is preferred over D2 for supplementation
- 5Take with fat and consider co-factors: K2-MK7 and magnesium
- 6Sun exposure remains the most natural source — 15-30 min midday when UV index > 3
- 7Test in late winter to see your baseline; retest 3 months after changing supplementation