Vitamin D3
The sunshine vitamin
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Always consult your physician before starting any supplement.
Vitamin D3 (cholecalciferol) is the form of vitamin D that your body produces when exposed to sunlight. It is a fat-soluble vitamin that plays a crucial role in calcium absorption, immune function, mood regulation, and muscle health.
Despite its importance, vitamin D deficiency is extremely common — especially in northern climates, among people with darker skin, and those who spend most of their time indoors. This is why we recommended testing and supplementing in our physical store more than almost any other nutrient.
Immune Function
Supports healthy immune response. Research suggests adequate vitamin D levels are associated with better immune function, especially during cold and flu season.
Bone Health
Essential for calcium absorption and bone mineralization. Critical for maintaining strong bones and teeth throughout life.
Mood Support
Low vitamin D levels are associated with low mood. Many people report improved mood and energy after correcting deficiency.
Muscle Function
Supports muscle strength and may help reduce the risk of falls in older adults.
Vitamin D supplements aren't all the same compound. The chemical form and delivery method both affect how well it actually raises your blood levels.
D3 (Cholecalciferol) — the one to buy
This is what your skin produces from sunlight, and it's what nearly every quality supplement uses. A systematic review and meta-analysis of randomized trials found D3 significantly more effective than D2 at raising and maintaining blood 25-hydroxyvitamin D levels. Check the label if you're buying a vegan product specifically — most D3 is sourced from lanolin (sheep's wool), so vegan versions use D3 from lichen instead, which is still D3, not the less-effective D2.
D2 (Ergocalciferol) — the less effective form
D2 is plant/fungal-derived and was historically the only vegan option, which is why some older vegan products and prescription high-dose vitamin D (often 50,000 IU) still use it. It works, but less efficiently — the same meta-analysis found meaningfully smaller and less sustained increases in blood levels compared to an equal dose of D3.
Delivery Form: Oil-Based Softgel vs. Dry Tablet
Vitamin D is fat-soluble, so it depends on dietary fat for absorption. An oil-based softgel (D3 suspended in olive oil, MCT oil, etc.) tends to absorb more reliably than a dry powder tablet, especially if you don't always remember to take it with a fatty meal. If you go with a tablet or gummy, taking it alongside food containing fat matters more.
- Get your levels tested — don't guess
- Take with a meal containing fat for better absorption
- Many people need 2,000–4,000 IU daily in winter months
- Works synergistically with Magnesium and Omega-3
Real toxicity is rare, but it happens — a review of published vitamin D overdose case reports found it's almost always caused by sustained megadosing (routinely well above 10,000 IU/day) or a manufacturing/dosing error, not typical supplementation at the doses on this page. Toxicity works through hypercalcemia (excess blood calcium), with symptoms like nausea, vomiting, weakness, and in severe cases kidney problems.
If you take a thiazide diuretic, vitamin D can raise your risk of hypercalcemia, since thiazides already reduce how much calcium your body excretes. And because hypercalcemia increases the risk of digoxin toxicity, anyone on digoxin combining it with vitamin D should have calcium and digoxin levels monitored by their doctor.
People with granulomatous diseases (like sarcoidosis or tuberculosis) or kidney disease can have abnormal vitamin D sensitivity and calcium regulation — talk to your doctor before supplementing, and don't guess your dose without a blood test if you fall into either group.
Vitamin D deficiency is one of the most common nutritional deficiencies worldwide. Numerous studies link adequate vitamin D levels with better immune function, bone health, and mood. Testing is the only way to know your personal needs.
What to look for
- "Cholecalciferol" or "D3" explicitly stated — not just "vitamin D" with no form specified
- An oil-based softgel for more reliable absorption, especially if you don't always take it with a fatty meal
- A clear IU (or mcg) amount per serving that matches your target dose — remember 1,000 IU = 25mcg if a label only lists mcg
- Third-party testing from a reputable manufacturer
Red flags
- No plant/animal source or form (D2 vs D3) disclosed anywhere on the label
- Extremely high single-dose softgels (25,000+ IU) marketed for daily use without a clear medical reason — these are typically meant for occasional/weekly dosing under supervision, not everyday use
- Gummies with no clear stated IU per gummy, or that require multiple gummies to hit a standard dose without saying so upfront
- Vague "vitamin D complex" labeling that doesn't specify D2 vs D3
How Vitamin D3 Compares
| Ingredient | Best For | Key Difference |
|---|---|---|
| Vitamin D3 | Immunity, Bones, Mood | Fat-soluble; needs sunlight or supplementation |
| Vitamin C | Daily immune support, Antioxidant | Water-soluble; excess is excreted |
| Zinc | Immune defense, Wound healing | Trace mineral; important for hormone health |
Vitamin D3 works especially well when paired with Magnesium and Omega-3.
Full stack recommendations available in our Stacks section. For the complete fat-soluble vitamin trio, also see our Vitamin K2 and Vitamin E guides.
- Holick MF, et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2011;96(7):1911–1930.
- Forrest KY, Stuhldreher WL. Prevalence and Correlates of Vitamin D Deficiency in US Adults. Nutr Res. 2011;31(1):48–54.
- Martineau AR, et al. Vitamin D Supplementation to Prevent Acute Respiratory Tract Infections. BMJ. 2017;356:i6583.
- Tripkovic L, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. 2012;95(6):1357–1364.
- Galior K, et al. Development of Vitamin D Toxicity from Overcorrection of Vitamin D Deficiency: A Review of Case Reports. Nutrients. 2018;10(8):953.
Evidence-based supplement recommendations from a former physical store owner. No hype. No BS. Just facts.
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