Sunlight & Bone Health

Fracture Risk

• Sunlight avoidance: 26% higher fracture risk
• Vitamin D <20 ng/mL: primary mediator
• Dose-response with UV exposure

Vitamin D Synthesis

• Summer: 1000-2000 IU/h of sun exposure
• Skin type affects efficiency
• Latitude limits winter synthesis

Clinical deficiency & skeletal pathways (review)

Holick 2007 (N Engl J Med; PMID 17634462; holick-2007-vitamin-d-deficiency-nejm) synthesizes photochemical vitamin D₃ formation in skin, why 25(OH)D tracks status, and how prolonged insufficiency links to rickets / osteomalacia / osteoporosis and fracture susceptibility—mechanism and prevention vocabulary to pair with Kirsch (prospective sunlight-avoidance cohort) and Lewis (sun exposure ↔ synthesis dose–response).

Oral calcium/vitamin D supplements vs fractures (RCT meta-analysis; community adults)

Zhao et al. 2017 (JAMA; PMID 29279934; zhao-2017-calcium-vitamin-d-fracture-meta-jama) pooled 33 RCTs (n ≈ 51,145, >50 y, community-dwelling): no significant fracture reduction for calcium, vitamin D, or combined supplements versus placebo/no treatment on hip, vertebral, or total fractures in abstract models—calibrates pill substitution claims next to UV-driven vitamin D synthesis and food-pattern adequacy on daily-sunlight.

Recommendations

• 15-30 min daily face and arm sun exposure
• Supplement if sunlight insufficient
• Target serum vitamin D >30 ng/mL

Tertiary map

Wikipedia: Vitamin D (wikipedia-vitamin-d-overview) covers cutaneous synthesis vs diet/supplements, 25(OH)D testing debates, and latitude/season limits—fracture and mortality statistics on this page still trace to PubMed-linked cohort and trial rows here, not encyclopedia tables alone.

Do not conflate with fish oil

Marine omega-3 (EPA/DHA) evidence lives under Marine Omega-3 Supplementation—a different axis from cutaneous vitamin D.