I asked my wife, a physician, how often she sees low VIT D levels in
patients in Massachusetts, she says about 2/3 of patients over 60 have
low levels and 1/3 in younger patients have low levels.   She sees low
levels in patients who take  multi-vitamins.   400 units a day is not
enough.

I feel patients who have  low levels have more periodontal disease.
Interesting to see that low levels also promote cancer as reported by
Canadian researchers today.

David DiBenedetto, DMD, author of "Insider's guide to Gum Disease,
Orthodontics, and Dentistry. What is not taught in dental school."