Vitamin D
Vitamin D3 — the hormone most people are deficient in. Bone health, immune function, testosterone, and all-cause mortality.
VERDICT
The Protocol says: Vitamin D supplementation is genuinely useful for a few specific things—preventing respiratory infections (especially if you're deficient), reducing fracture risk in older adults at higher doses, and improving bone density in children—but it's not a longevity miracle. Don't expect it to prevent cancer, heart disease, or extend your life.
Key Findings
- Vitamin D supplementation reduces acute respiratory infections, with substantially stronger effects in people with severe deficiency.
- Doses above 700 IU daily reduce hip and nonvertebral fractures in older adults, though supplements alone don't prevent all fracture types.
- Vitamin D3 is roughly twice as effective as D2 at raising blood levels, making it the better supplementation choice.
- Vitamin D supplements did not reduce cardiovascular disease, cancer incidence, cancer mortality, or overall mortality in large randomized trials.
- Type 2 diabetes risk dropped 20% with supplementation in older adults without prediabetes, a meaningful but population-specific benefit.
- Long-term supplementation is safe with no serious adverse effects beyond placebo rates.
All Studies (50)
Sorted by impact. Each study summarized in one sentence.
Vitamin D3 supplementation over 5 years showed no effect on cardiovascular disease or cancer incidence in older adults.
No protection against heart disease or cancer
Vitamin D supplementation reduced type 2 diabetes risk by 20% in older US adults without prediabetes.
20% lower diabetes risk in general population
Vitamin D supplementation did not significantly reduce overall mortality in adults across multiple randomized trials.
No clear mortality benefit from vitamin D alone
Vitamin D supplements alone modestly increased bone density but did not prevent fractures in older adults.
Bone density improves, but fracture prevention unclear
Vitamin D3 supplementation did not reduce cancer deaths in general populations or cancer patients.
No cancer mortality reduction from vitamin D3
Vitamin D, omega-3, and strength training alone showed minimal benefits; combined use produced modest health improvements in older adults.
Modest benefits mainly when interventions combined
Vitamin D supplementation reduced hip and nonvertebral fractures in older adults, especially at doses above 700 IU daily.
Higher doses reduce fracture risk in seniors
Vitamin D supplementation reduced acute respiratory infections, with stronger effects in people with severe deficiency.
Vitamin D cuts respiratory infection risk significantly
Vitamin D supplementation prevents deficiency and improves bone health in exclusively breastfed infants at risk of insufficiency.
Supplementation prevents rickets in breastfed infants
Achieving vitamin D sufficiency reduced upper respiratory infections in military recruits; sunlight and oral D3 were equally effective.
Sufficiency reduces infections in active adults
Vitamin D2 supplementation reduced COVID-19 infection risk and symptom severity in healthcare workers over 12 weeks.
Lowers COVID-19 risk and symptom severity
Pregnant women taking vitamin D supplements gave birth to children with denser bones at ages 4-6 years.
Prenatal vitamin D improves child bone density
Long-term vitamin D supplementation doesn't cause common side effects beyond those in placebo groups.
No serious adverse effects at normal doses
Vitamin D supplements do not reduce cancer risk in healthy adults based on clinical trial evidence.
No cancer prevention benefit shown
Vitamin D3 raises blood vitamin D levels about twice as effectively as D2 at equivalent doses.
D3 superior to D2 for raising vitamin D status
Long-term vitamin D supplementation in deficient children improved growth and delayed early puberty onset.
Vitamin D supports child growth and normal pubertal timing
Vitamin D3 outperforms D2 across different doses; higher BMI reduces vitamin D absorption effectiveness.
D3 superior; overweight people need more vitamin D
High-dose vitamin D injections (50k-500k IU) altered free vitamin D metabolites but effects on bone and physical function unclear.
Mega-doses alter vitamin D metabolism unpredictably
High-dose vitamin D3 as add-on therapy for multiple sclerosis showed mixed results across randomized trials.
Uncertain benefit for multiple sclerosis progression
Weekly vitamin D dosing works as well as daily dosing for correcting deficiency, reducing pill burden.
Weekly dosing equals daily for deficiency correction
Vitamin D3 at 15 mcg daily raised blood levels better than D2 in both South Asian and European women.
D3 superior to D2 at low supplemental doses
Vitamin D supplementation showed modest improvements in muscle strength and physical function across multiple randomized trials.
Modest gains in muscle strength and function
Weekly vitamin D supplementation improved eczema severity and reduced immune inflammation markers in children with atopic dermatitis.
Improves eczema and reduces inflammation
Vitamin D supplementation improved bone health markers and immune function in HIV-positive children and young adults.
Strengthens bones and immune response
Vitamin D3 supplementation (4000-5000 IU for 8 weeks) reduced nasal symptoms and improved allergic rhinitis in Mexican patients.
Reduces allergic rhinitis symptoms
Maternal vitamin D supplementation during breastfeeding increased vitamin D levels in both mother and nursing infant.
Boosts vitamin D in mother and baby
Children on epilepsy medications have a 32% prevalence of vitamin D deficiency, suggesting they need monitoring.
Epilepsy drugs increase vitamin D deficiency risk
Vitamin D3 supplementation in athletes improves muscle strength and raises serum vitamin D levels.
Boosts muscle strength in athletic populations
Vitamin D supplementation does not reduce arterial stiffness in randomized trials despite claims about cardiovascular benefit.
No effect on arterial stiffness in RCTs
Low vitamin D levels may weaken flu vaccine effectiveness, but evidence remains unclear and mixed.
Deficiency may reduce flu vaccine response
Vitamin D supplements modestly reduced respiratory infections in healthy adults and children, but effect varies.
Modest reduction in cold/flu infections
High-dose vitamin D improved survival and reduced organ failure in septic patients on ventilators.
High-dose improves sepsis survival outcomes
Vitamin D supplements improved mood and physical function in African American diabetics with depression.
Reduces depression, improves function in diabetics
Weekly vitamin D reduced respiratory infections in young children, with stronger effects in southern latitudes.
Weekly supplementation cuts infection risk
Maternal vitamin D supplementation while breastfeeding improves infant vitamin D status and bone development.
Maternal supplementation boosts infant vitamin D
Vitamin D supplementation showed inconsistent effects on muscle strength in athletes across studies.
No consistent muscle strength benefit for athletes
Vitamin D levels correlate with dental implant success, but evidence quality remains limited across seven human studies reviewed.
Vitamin D may improve dental implant outcomes
Combined vitamin D and magnesium supplementation did not improve bone turnover markers or blood sugar control after 12 weeks.
No effect on bone or metabolic health markers
Vitamin D3 supplementation had minimal effect on reducing body fat percentage in overweight and obese adults.
Little to no impact on body fat loss
Vitamin D supplementation moderately increased fibroblast growth factor-23, a hormone involved in mineral metabolism.
Raises FGF-23 hormone levels
Vitamin D supplementation improved survival rates in animals with malaria infection in experimental studies.
Improves survival in malaria infection
4000 IU daily vitamin D3 for 12 weeks altered gut bacteria composition and metabolite production in healthy adults.
Changes gut microbiome composition
Vitamin D supplementation for sickle cell disease patients may help reduce complications from the chronic inflammatory condition.
Potential benefit in sickle cell disease management
Vitamin D supplementation may help sickle cell patients overcome nutritional deficits caused by the disease.
Addresses multiple nutrient gaps in sickle cell
Vitamin D supplementation in chronic liver disease shows potential benefits but requires more high-quality evidence.
May help liver disease patients, evidence limited
Paricalcitol is more effective than other vitamin D drugs at lowering calcium and phosphorus in dialysis patients.
Paricalcitol outperforms other vitamin D drugs
Premature babies given 800 IU daily vitamin D achieved better vitamin D status than those given 400 IU.
800 IU daily superior to 400 IU in preemies
Paricalcitol works as well as other vitamin D drugs for kidney disease patients with high parathyroid hormone.
Paricalcitol comparable to non-selective vitamin D activators
Vitamin D2 supplementation increases blood vitamin D levels, with higher doses producing larger increases.
Dose-dependent increase in vitamin D levels
Vitamin D supplementation in kidney disease patients affects blood vessel growth markers, with clinical significance unclear.
Affects angiogenic markers in kidney disease