Proof of that???
Something like this?http://jcem.endojournals.org/cgi/content/abstract/92/6/2130
The Journal of Clinical Endocrinology & Metabolism, doi:10.1210/jc.2006-2250
The Journal of Clinical Endocrinology & Metabolism Vol. 92, No. 6 2130-2135
Copyright © 2007 by The Endocrine Society
Low Vitamin D Status despite Abundant Sun Exposure
N. Binkley, R. Novotny, D. Krueger, T. Kawahara, Y. G. Daida, G. Lensmeyer, B. W. Hollis and M. K. Drezner
Context: Lack of sun exposure is widely accepted as the primary cause of epidemic low vitamin D status worldwide. However, some individuals with seemingly adequate UV exposure have been reported to have low serum 25-hydroxyvitamin D [25(OH)D] concentration, results that might have been confounded by imprecision of the assays used.
Objective: The aim was to document the 25(OH)D status of healthy individuals with habitually high sun exposure.
Setting: This study was conducted in a convenience sample of adults in Honolulu, Hawaii (latitude 21°).
Participants: The study population consisted of 93 adults (30 women and 63 men) with a mean (SEM) age and body mass index of 24.0 yr (0.7) and 23.6 kg/m2 (0.4), respectively. Their self-reported sun exposure was 28.9 (1.5) h/wk, yielding a calculated sun exposure index of 11.1 (0.7).
Main Outcome Measures: Serum 25(OH)D concentration was measured using a precise HPLC assay. Low vitamin D status was defined as a circulating 25(OH)D concentration less than 30 ng/ml.
Results: Mean serum 25(OH)D concentration was 31.6 ng/ml. Using a cutpoint of 30 ng/ml, 51% of this population had low vitamin D status. The highest 25(OH)D concentration was 62 ng/ml.
Conclusions: These data suggest that variable responsiveness to UVB radiation is evident among individuals, causing some to have low vitamin D status despite abundant sun exposure. In addition, because the maximal 25(OH)D concentration produced by natural UV exposure appears to be approximately 60 ng/ml, it seems prudent to use this value as an upper limit when prescribing vitamin D supplementation.
Note, some have low D and some are fine. Blood testing is the only way to know for any given individual.