The major argument seems to be between Professor Holick defining anything short of optimal as a deficiency, while Professor Gilchrest takes a more holistic view that vitamin D defficiency is not a major issue in Boston compared to other lifestyle based health issues. I side with Professor Gilchrest here. Avoiding the HUGE sun damage of sunburns and deliberate tanning is basically good enough. Personally, I feel driving my convertible with the top down and wearing a hat on short trips to be enough sun exposure. An early warning signs of too little sun = seasonal depression. An early warning sign of too much sun = tanned or red skin. Anything in between = C average, pay attention to other health issues. AS AN EXAMPLE: If you want healthy glowing skin, go vegetarian. Middle-aged vegetarians generally have skin tone and appearance most americans with an 'average diet' lose in their late twenties. Unless you are a habitual dark tanner or burner, diet affects your skin more than sun exposure.