We Do Science - The Sports Nutrition Podcast Episode 12 - 'Vitamin D' with Graeme Close PhD
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Aug 27, 2014 
Graeme Close PhD, senior lecturer and sports nutrition researcher known for work on vitamin D and elite athletes. He discusses what vitamin D actually is and why research exploded. They cover sunlight and dietary limits, pros and cons of supplementation, testing methods, dosing strategies, and where evidence is strongest versus still uncertain.
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Don't Rely On Winter Sun For Vitamin D
- Avoid relying on winter sun at northern latitudes because the sun's zenith angle often prevents skin conversion to vitamin D.
- Graeme Close: if your shadow is taller than you, the sun angle is probably too low for vitamin D synthesis.
Prefer Regulated Sunlight Over High Dose Tablets
- Prefer sensible, limited sun exposure for natural regulation of vitamin D production rather than high-dose oral intake when possible.
- Graeme Close notes skin produces inner photoproducts that prevent systemic toxicity from excess sunlight-derived vitamin D.
Dietary Vitamin D Is Often Insufficient And Less Potent
- Dietary vitamin D is usually low and often D2, which is less effective than sunlight-derived D3.
- Graeme Close warns some fortified foods contain negligible vitamin D and D2's activity is ~9.5x lower than D3.