William Grant: Vitamin D reduces the risk of 8 of the top 10 causes of death

William Grant: Vitamin D reduces risk of 8 of the top 10 causes of death – April 2026

Presentation: Vitamin D and Health at The Real Truth About Health Conference

Presenter: William B. Grant, PhD – Sunlight, Nutrition and Health Research Center, San Francisco, CA

Date: April 9, 2026 PDF

Overview

Physicist-turned-epidemiologist William B. Grant delivered a comprehensive review of the evidence for vitamin D's health benefits at the April 2026 Real Truth About Health conference. His central conclusion: raising serum 25(OH)D above 30 ng/mL can significantly reduce the burden of 8 of the top 10 causes of death in the United States — heart disease, cancer, COVID-19, stroke, chronic lower respiratory disease, Alzheimer's disease and other dementias, diabetes mellitus, and kidney disease.

Grant also noted that vitamin D is "the lowest-cost major contributor to health" and that extra-skeletal benefits have been the focus of intensive research over the past 25 years.

About William B. Grant, PhD

PhD in Physics, UC Berkeley, 1971
30-year career in laser remote sensing, including 15 years at NASA Langley Research Center
Learned epidemiological methods (ecological studies) from a forestry professor while studying effects of air pollution on eastern forests for the Sierra Club
First ecological health study (1997): dietary links to Alzheimer's disease
Founder, Sunlight, Nutrition and Health Research Center (SUNARC), San Francisco
Funded by Bio-Tech Pharmacal, Inc. (Fayetteville, AR), a vitamin D supplement supplier
Co-author of the landmark 2025 Nutrients review: Vitamin D: Evidence-Based Health Benefits and Recommendations for Population Guidelines (Grant et al., Nutrients 2025;17(2):277)

Types of Evidence Covered

Grant organized the evidence into three tiers:

Observational studies — ecological, prospective cohort, cross-sectional, and case-control studies. These form the strongest evidence base for vitamin D, because they capture real-world variation in 25(OH)D levels across populations.

Randomized controlled trials (RCTs) — Grant explained why most vitamin D RCTs have failed to show benefit: they were designed like pharmaceutical drug trials (using guidelines not suited to nutrients), enrolled participants with already-adequate baseline 25(OH)D levels, used doses too low to move levels meaningfully, and did not analyze outcomes by achieved serum level. He highlighted two well-designed RCTs that did show benefit:- D2d Study (prediabetes to diabetes): participants achieving intratrial 25(OH)D ≥50 ng/mL had substantially lower risk of diabetes progression- Pregnancy and birth outcomes RCT: 25(OH)D >40 ng/mL associated with ~60% lower preterm birth risk in 1,064 pregnant women

Mechanisms — Vitamin D's biological plausibility is supported by the fact that 25(OH)D regulates broad gene expression. A dose-response study (Shirvani, Holick et al., Sci Rep 2019) found that 10,000 IU/day regulated 1,289 genes in white blood cells, versus 320 at 4,000 IU/day and only 162 at 600 IU/day.

Key Health Areas Reviewed

Pregnancy and Birth Outcomes

Serum 25(OH)D >40 ng/mL associated with ~60% lower preterm birth risk
Endorsed for supplementation in high-risk pregnancies (preeclampsia, intrauterine mortality, preterm birth, small-for-gestational-age, neonatal mortality) — Demay, Pittas et al., J Clin Endocrinol Metab

Cancer

Ecological studies show strong inverse correlation between solar UVB exposure and breast cancer mortality (Grant, 2002; Grant & Garland, Anticancer Res 2006)
VITAL study (25,000 participants, 2,000 IU/day): cancer mortality reduced
AMATERASU trial: vitamin D improved relapse-free survival in p53-positive digestive tract cancers
Grant's estimate from 2026 US cancer statistics: a 10% reduction in cancer incidence attributable to adequate UVB/vitamin D would prevent ~211,000 new cases and ~63,000 deaths annually

Cardiovascular Disease

Vitamin D deficiency associated with vascular dysfunction, arterial stiffening, and left ventricular hypertrophy
Prospective cohort studies show consistent inverse relationship between 25(OH)D and CVD incidence/mortality (though RCTs have been inconclusive due to design flaws)

COVID-19

Vitamin D research peaked in 2020 in association with COVID-19
Wimalawansa (Biomedicines 2023): maintaining population vitamin D sufficiency above 40 ng/mL is the most cost-effective way to reduce severity of viral epidemics and pandemics

Dental Caries

Covered in the presentation outline (slide details not fully extracted)

Alzheimer's Disease and Dementia

Grant's research interest in Alzheimer's dates to his first 1997 paper. The presentation covered vitamin D's role in multiple dementia risk factors:

Inflammation — Moszura et al., Nutrients 2026;18(4):577
Insulin resistance — prediabetes/diabetes progression (D2d study)
Infections — vitamin D's immune-modulating role
Lipids — vitamin D's role in metabolic health
Sleep — key finding below

Sleep and Mental Health

Meta-analysis (Ungvari et al., Geroscience 2025): sleep disorders increase dementia risk by 33–45%; insomnia increases AD risk by 49%
Vitamin D reduces sleep disorder risk by ~48–52% in people with prediabetes and diabetes over 13 years (Liu et al., Front Endocrinol 2025)
Vitamin D protects against depression — umbrella meta-analysis of 10 RCTs: pooled SMD −0.40 (95% CI: −0.60, −0.21); cohort studies show 60% higher odds of depression with low vitamin D (Musazadeh et al., Pharmacol Res 2023)

Sun Exposure

~80–90% of serum 25(OH)D comes from solar UVB
Shadow rule: vitamin D production is most efficient when your shadow is shorter than your height
US food intake provides only ~250 IU/day — far below therapeutic range
Most people develop a tan that blocks 50–75% of UV; gradual spring/summer sun exposure is recommended
Avoiding sun exposure is itself a risk factor: a 20-year Swedish cohort of 29,518 women found that active sun exposure habits were associated with lower cardiovascular and non-cancer/non-CVD mortality (Lindqvist et al., J Intern Med 2016)
High-dose oral vitamin D (200,000 IU) given one hour after experimental sunburn reduced proinflammatory mediators TNF-α and iNOS, and promoted skin barrier repair genes (Scott et al., J Invest Dermatol 2017)
Sunlight has vitamin D-independent benefits via photomobilization of nitric oxide from cutaneous stores, reducing cardiovascular morbidity (Weller, J Invest Dermatol 2024)

Dosing Recommendations

Goal	Recommended dose
Minimum sufficiency (>30 ng/mL)	2,000 IU/day vitamin D3
Target for obese individuals	4,000–5,000 IU/day
Optimal protection (40–70 ng/mL)	4,000–6,000 IU/day
Rapid repletion (not previously supplementing)	10,000 IU/day for 10–15 days

Grant recommends measuring your 25(OH)D level (wet blood or dried blood spot) — ideally as part of an annual physical — to calibrate supplementation to your personal goal.

Note: 25% of the US population and 60% of Central Europeans have levels below 20 ng/mL.

Vitamin D Life Referenced in This Presentation

Dr. Grant's closing "For More Information" slide explicitly recommends Vitamin D Life:

"Vitamin D Life continues to be the world's most comprehensive website on Vitamin D. It has >14,400 curated pages of evidence-based studies, overviews, charts, and meta-analyses."

He also cited the Vitamin D Life "Proof That Vitamin D Works" page listing 99 health conditions for which vitamin D has proven benefit:

Key References Cited

Grant et al. Nutrients. 2025;17(2):277 — Evidence-Based Health Benefits and Recommendations for Population Guidelines
Wimalawansa SJ. Biomedicines. 2023;11(6):1542 — Physiological basis for using vitamin D
Shirvani, Holick et al. Sci Rep. 2019;9(1):17685 — Gene expression dose-response study
Liu et al. Front Endocrinol. 2025;16:1524368 — Vitamin D and sleep disorder risk
Musazadeh et al. Pharmacol Res. 2023;187:106605 — Vitamin D and depression umbrella meta-analysis
Ungvari et al. Geroscience. 2025 — Sleep disorders and dementia risk meta-analysis
Lindqvist PG et al. J Intern Med. 2016;280(4):375-87 — Sun avoidance and all-cause mortality
Scott JF et al. J Invest Dermatol. 2017;137(10):2078-2086 — Oral vitamin D and sunburn inflammation
Siegel RL et al. CA Cancer J Clin. 2026;e70043 — Cancer statistics 2026
Moszura et al. Nutrients 2026;18(4):577 — Vitamin D and inflammation
Kroll MH et al. (Holick MF). PLoS One. 2015;10(3):e0118108 — Seasonal 25(OH)D patterns