Vitamin D3 (Cholecalciferol)
The sunshine vitamin that over 40% of Americans are deficient in
Also known as: Cholecalciferol • Vitamin D • The Sunshine Vitamin
Overview
Vitamin D3, also known as cholecalciferol, is a fat-soluble vitamin that the body produces when skin is exposed to ultraviolet B (UVB) radiation from sunlight. It plays a critical role in calcium absorption, bone health, immune function, mood regulation, and muscle performance. Despite its importance, vitamin D deficiency is remarkably common — studies estimate that approximately 42% of American adults have insufficient levels, with rates even higher among older adults, people with darker skin, and those living in northern latitudes. Supplementation with D3 (the animal-derived form) is generally preferred over D2 (ergocalciferol) because D3 raises and maintains serum 25(OH)D levels more effectively. The Endocrine Society recommends that adults at risk of deficiency take 1,500–2,000 IU daily, though many functional medicine practitioners suggest higher doses of 4,000–5,000 IU based on individual blood levels.
Key Benefits
Bone Health & Calcium Absorption
Vitamin D3 is essential for intestinal calcium absorption. Without adequate vitamin D, the body can only absorb 10–15% of dietary calcium, compared to 30–40% with sufficient levels. This makes D3 critical for preventing osteoporosis and fractures, especially in older adults.
Immune System Support
Vitamin D receptors are found on virtually all immune cells. D3 enhances the pathogen-fighting effects of monocytes and macrophages, and modulates the adaptive immune system. Multiple meta-analyses show that supplementation reduces the risk of acute respiratory infections by 12–75%, with the greatest benefit in those who are deficient.
Mood & Mental Health
Low vitamin D levels are consistently associated with higher rates of depression. The vitamin plays a role in serotonin synthesis, and several randomized controlled trials have shown that supplementation can improve depressive symptoms, particularly in those with baseline deficiency.
Muscle Function & Athletic Performance
Vitamin D receptors are present in skeletal muscle tissue. Adequate levels support muscle protein synthesis, muscle strength, and neuromuscular function. Athletes with sufficient D3 levels show improved power output, reduced injury risk, and faster recovery times.
Cardiovascular Health
Observational studies link low vitamin D with increased cardiovascular risk. D3 may help regulate blood pressure through its effects on the renin-angiotensin system, and support endothelial function. However, intervention trials have shown mixed results for cardiovascular endpoints.
Dosage & How to Take
Most adults benefit from 1,000–5,000 IU of vitamin D3 daily. The optimal dose depends on current blood levels, body weight, skin color, sun exposure, and geographic location. Blood testing for 25(OH)D is the gold standard for determining individual needs.
| Purpose | Dose | Notes |
|---|---|---|
| General maintenance | 1,000–2,000 IU/day | For adults with some sun exposure |
| Deficiency correction | 5,000–10,000 IU/day for 8–12 weeks | Under medical supervision, then reduce to maintenance |
| Optimal levels (40–60 ng/mL) | 2,000–5,000 IU/day | Adjusted based on blood work every 3–6 months |
| Obese individuals | 3,000–6,000 IU/day | Higher doses needed due to sequestration in fat tissue |
Best Time to Take
Take in the morning or early afternoon with a meal containing fat. Some evidence suggests evening dosing may interfere with melatonin production and sleep quality.
With or Without Food
Always take with a fat-containing meal. Studies show absorption increases by 50% when taken with dietary fat compared to on an empty stomach.
Forms & Bioavailability
| Form | Absorption | Best For | Notes |
|---|---|---|---|
| D3 Softgel (oil-based) | High | General supplementation | Pre-dissolved in oil for optimal absorption. Most studied form. |
| D3 Liquid Drops | High | Flexible dosing, children | Easy to adjust dose. Can be added to food or drinks. |
| D3 Tablet/Capsule (dry) | Moderate | Budget option | Take with fatty food to improve absorption. |
| D2 (Ergocalciferol) | Lower | Vegan option | Plant-derived but less effective at raising blood levels. Requires higher doses. |
| D3 from Lichen (Vegan) | High | Vegan supplementation | Plant-sourced D3 with equivalent bioavailability to animal-derived D3. |
Side Effects & Safety
Common
- Generally very well tolerated
- Mild nausea at high doses
- Constipation (rare, usually with calcium co-supplementation)
Rare
- Hypercalcemia (at very high doses >10,000 IU/day long-term)
- Kidney stones (in susceptible individuals)
- Soft tissue calcification (toxicity only)
Contraindications
- Hypercalcemia
- Granulomatous diseases (sarcoidosis)
- Severe kidney disease (consult physician)
- Williams syndrome
Interactions
Synergistic — K2 directs calcium to bones and away from arteries. Recommended to take together.
Magnesium is required for vitamin D metabolism. Deficiency in magnesium can impair D3 activation.
Some statins may reduce vitamin D levels. Monitor and supplement accordingly.
Can increase calcium levels when combined with high-dose D3. Monitor calcium.
Long-term use impairs vitamin D metabolism and calcium absorption. Higher D3 doses may be needed.
Scientific Research
Vitamin D and Respiratory Infections
Meta-analysis of 25 RCTs found daily or weekly D3 supplementation reduced risk of acute respiratory tract infections by 12% overall, and by 70% in those with severe deficiency.
Vitamin D and Depression
Systematic review of 41 studies found that vitamin D supplementation had a statistically significant effect on reducing depressive symptoms, with effect sizes comparable to some antidepressant medications.
Vitamin D and All-Cause Mortality
Large-scale analysis of over 300,000 participants found that serum 25(OH)D levels below 20 ng/mL were associated with a 25% increased risk of all-cause mortality.
D3 vs. D2 Effectiveness
Head-to-head comparison showed D3 was approximately 87% more potent than D2 in raising and maintaining serum 25(OH)D concentrations.
Food Sources
Frequently Asked Questions
Medical Disclaimer
This content is for educational and informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare professional before starting any supplement regimen, especially if you have pre-existing health conditions or are taking medications. The statements on this page have not been evaluated by the Food and Drug Administration.