I have taken vit D combined with cal and mag for years. Recently adding some K2. My logic being, that having worked on an orthopaedic ward that I didn't want to end up with a fractured femur after the menopause. However something else has happened. Following a epidemic of influenza a couple of years ago I was the last man standing. I watched my colleges go down one by one and knew that it was eventually going to get me but it didn't . Following on from this it dawned on me that I'm never ill. I've not had a cold for over fifteen years and my annual bouts of tonsillitis have also long gone. I casually mentioned this to a person who was talking about how nutrition can help us with our immunity. She immediately asked if I was taking vit D. When I said I was, for prevention against loss of bone density after the menopause, she told me that was the reason why I didn't get ill. So this book backs up this theory. It would be great if it prevented all the other things mentioned as that would mean that I unwittingly have set my self up for a healthier life in my old age. I am now wondering, if at 50 that my ability to be more active than many of my friends is also down to vit D. This has the added benefit of saving me from the dreaded middle age spread. I don't mean going to the gym every day. I never go there. I just seem to be able to do more on less sleep. Who knows ????