How much vitamin D do I need?

Most people need 2,000-4,000 IU daily to reach optimal levels (40-60 ng/mL). Test your levels to know for sure.

Can I get enough from sun?

15-20 minutes of midday sun (arms/legs exposed, no sunscreen) produces ~10,000 IU. But this requires UVB availability. Impossible in winter at high latitudes.

Should I take K2 with vitamin D?

Yes, especially at doses >2,000 IU. K2 directs calcium to bones rather than arteries. MK-7 form is best.

supplement

47,000+ trials analyzed

59,000+ interactions

Not FDA evaluated

Vitamin D: Complete Guide

Q: D2 vs D3: which is better?

D3 is 87% more effective at raising blood levels and has longer shelf life. Use D3 unless you're strictly vegan.

The "sunshine vitamin" that 42% of Americans are deficient in. Critical for immunity, bones, and mood.

Quick Summary

The "sunshine vitamin" that 42% of Americans are deficient in. Critical for immunity, bones, and mood. 1,000-2,000 IU daily for maintenance. Best form: D3 (Cholecalciferol).

Proven Benefits

Forms Available

Use Cases

What is Vitamin D?

Vitamin D is a fat-soluble hormone precursor that your skin produces from sunlight. It regulates calcium absorption, immune function, and over 200 genes. Unlike most vitamins, it acts more like a hormone, affecting nearly every cell in your body.

Who Should Consider Vitamin D?

Anyone living above 35°N latitude (most of US/Europe)
People with darker skin (need more sun exposure)
Those who work indoors or use sunscreen
Adults over 65 (skin produces 75% less vitamin D)
People with depression, especially seasonal
Those with autoimmune conditions

How It Works

When you take vitamin D3, your liver converts it to 25(OH)D (what blood tests measure). Your kidneys then activate it to 1,25(OH)D, which binds to vitamin D receptors throughout your body, regulating gene expression for immunity, mood, and bone health.

Forms Comparison

Different forms of Vitamin D have varying absorption rates and best uses. Here's how they compare:

Form	Bioavailability	Best For
D3 (Cholecalciferol)	90%	Everyone. mimics what skin produces, more effective than D2
D2 (Ergocalciferol)	50%	Vegans only (plant-derived). less effective but vegan-friendly

Our recommendation: D3 (Cholecalciferol) for most people due to superior absorption and tolerability.

Benefits & Evidence

Vitamin D has 2 strongly-evidenced benefits and 2 moderately-evidenced benefits.

Immune function

strong evidence

40% reduction in respiratory infections with adequate levels

Bone health

strong evidence

Essential for calcium absorption; prevents osteoporosis

Mood & depression

moderate evidence

Deficiency linked to 14% higher depression risk

Muscle function

moderate evidence

Reduces fall risk by 19% in elderly

Autoimmune support

emerging evidence

May reduce risk of MS, Type 1 diabetes, RA

Dosing & Timing

Recommended Doses

Standard Dose1,000-2,000 IU daily for maintenance

Clinical Dose4,000-5,000 IU daily if deficient (<30 ng/mL)

Maximum Daily10,000 IU daily without medical supervision

Timing

When to TakeMorning with breakfast (fat-containing meal)

With Food?Yes - improves absorption

DurationLifelong if sun exposure is limited; test levels annually

Side Effects & Interactions

Possible Side Effects

Hypercalcemia (at very high doses). Rare
Nausea. Uncommon

Interactions to Know

Requires adequate magnesium for activation
Pair with K2 for bone benefits (directs calcium to bones)
May interact with some heart medications
Synergistic with omega-3 for inflammation

Frequently Asked Questions