Demographic Trends of Vit D Insufficiency in the US 1988-2004
http://www.tantoday.com/forums/science-uv/40195-demographic-trends-vit-d-insufficiency-us-1988-2004-a.html April 2010
Because exposure to UV-B rays is the primary determinant of vitamin D status in humans, this is more likely the primary cause of the increasing prevalence of vitamin D insufficiency.29
Although widespread campaigns for sunscreen use and sun avoidance, including Healthy People 2010, have reduced the incidence of skin cancers,34 sunscreen with a sun protection factor of 15 also decreases the synthesis of vitamin D3 by 99%.35
Increased sunscreen use with a higher sun protection factor likely contributed to the reported trend of lower 25(OH)D levels.
In addition, decreased outdoor activity and obesity have been associated with vitamin D insufficiency.30, 36
The increased inactivity and obesity in the US population has likely contributed to the observed rise in vitamin D insufficiency.37
Previously published data suggested that vitamin D insufficiency was more prevalent among older adults (owing to reduction of 7-dehydrocholesterol levels in skin), women (owing to lower outdoor activity), and individuals with darker skin (owing to increased melanin).26, 30, 32
We found that previous differences by age and sex have equalized, but those by race/ethnicity have remained.
The loss of age- and sex-related differences may be secondary to disproportionately greater time indoors (eg, with television, computers, and video games) and less time outdoors among younger compared with older individuals and males compared with females.
Percentage having 30ng has fallen by half for many groups