Internet generation at risk of rickets (chronic lack of Vit D)
breitbart.com
breitbart.com
It turns out that as you age, your ability to absorb vitamin D through sunlight decreases, so past 40, you probably need supplementation.
I simultaneously did two things starting Jan 1: I stopped eating wheat and started taking vitamin D. Although I can't pinpoint which of these is the determining factor, I can report that I have much more energy (no post lunch drag, nor desire to nap after work) as a result. I also seem to sleep better. Check out:
http://heartscanblog.blogspot.com/2010/01/getting-vitamin-d-...
It costs almost nothing. A bottle of 360 softgels each containing 2,000 UI costs about $25 (Carlson Laboratories brand).
Just make sure you also take enough vitamin A.
For comparison that's about how much Vitamin D your skin will produce by being in the sun for 5-10 minutes (assuming you're in normal latitudes and have uncovered face, hands, arms - not always true in the winter).