I don't know, I was surprised to learn that my vitamin D was quite low, and I get a fair amount of sunlight each week, probably more than a lot of office workers.
Now that I take supplements though my levels have been fine. From what I have read, quite a few people fall into a similar bucket.
Honestly no, but I believe there is some research showing potential long term health benefits of avoiding low vitamin D. It's totally possible I'm wasting my money, but I'm happy with the potential benefit/cost ratio. I would gladly pay the price of some vitamins for even a small chance of avoiding significant health problems.
Now that I take supplements though my levels have been fine. From what I have read, quite a few people fall into a similar bucket.