Beeing aware of the Vitamin D subject in the mid-nineties longtime I forgot about it. Meanwhile there is a hype around Vitamin D supplementation, but it´s a very healthy hype I guess, that will on the long run leave the doctors and the pharma concerns poor. As my primary care physician told me recently: „Tell that to the people and I have to close my office!“ The skin can only convert sunlight into Vitamin D if certain conditions are fullfilled. Sunscreening for example prevents a Vitamin D production of the skin. Minimum activating UV factor is: 3 or bigger. Older or overweighted people have a stronger need. In our latitudes like Northern Germany or Alaska Vitamin D deficiency prevails from November to March, at least. Therefore there is a wideknown susceptibility to infections and „winter depressions“ – unless you go on holidays to southern countries in winter, then you’re fine. A level test could be made by a doctor. The optimal blood serum is between 50 ng/ml and 90 ng/ml. Adequate Vitamin D levels can prevent numerous diseases in old age: osteoporosis, dementia, calcification of the arteries and many others. Supplementation should be done together with Magnesium and Vitamin K2. Sports in fresh air do help a lot, same does Vitamin C.