In this episode of Longevity Roadmap, renowned endocrinologist Dr. Michael Holick unpacks the science behind vitamin D, its role as a hormone, and why maintaining optimal levels is critical for health and healthy ageing. From immune defence to chronic disease prevention, Holick shares decades of research and practical advice on how to get—and stay—vitamin D sufficient.

Key Points:

Dr. Michael Holick highlights vitamin D as a foundational hormone essential for immunity, bone health, and longevity. Simple steps like supplementation and sensible sun exposure can dramatically reduce disease risk and improve overall wellbeing.

• Vitamin D is a hormone, not a vitamin: Synthesized through skin exposure to UVB rays and activated in the liver and kidneys, vitamin D plays a key hormonal role in calcium metabolism, immune function, and cellular health.
• Deficiency is widespread—even in sunny places: Many people, even in regions like Southern California, are deficient due to limited UVB exposure during peak hours or sunscreen use. Darker skin, latitude, and time of day affect synthesis.
• Strong evidence for immune and disease protection: Adequate vitamin D levels support both innate and adaptive immunity, lower risk for respiratory infections, and may reduce the likelihood of autoimmune diseases, heart disease, and cancer progression.
• Supplementation is safe and necessary: Dr. Holick recommends 2,000–5,000 IU daily for most adults, more if obese. Toxicity is rare and typically requires massive overdoses. Levels of 40–60 ng/mL are ideal.
• Sunlight offers additional benefits: Sun exposure not only produces vitamin D but also induces other compounds like beta-endorphins and nitric oxide, contributing to mood, vascular health, and potentially skin cancer protection.