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Medical Forum / General / Nutrition / May 2007Low vitamin D status despite abundant sun exposure
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 University of Wisconsin Osteoporosis Clinical Research Program, Madison, WI; Human Nutrition, Food and Animal Sciences, University of Hawaii at Manoa, Honolulu, HI; Laboratory Medicine, University of Wisconsin, Madison, WI; Medical University of South Carolina, Charleston, SC 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 which might have been confounded by imprecision of the assays employed. Objective: The objective of this study 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, HI, (latitude 21°). Participants: The study population consisted of 93 adults 30 women and 63 men, mean (SEM) age and BMI of 24.0 (0.7) years and 23.6 (0.4) kg/ m2 respectively. Their self-reported sun exposure was 28.9 (1.5) hours/ week 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 < 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. Conclusion: These data suggest that variable responsivity to UVB radiation is evident among individuals, causing some to have low vitamin D status despite abundant sun exposure. Additionally, as the maximal 25(OH)D concentration produced by natural UV exposure appears to be 60 ng/ml, it seems prudent to utilize this value as an upper limit when prescribing vitamin D supplementation. Marilyn > Setting: This study was conducted in a convenience sample of adults in > Honolulu, HI, (latitude 21°). > > Participants: The study population consisted of 93 adults 30 women and > 63 men, mean (SEM) age and BMI of 24.0 (0.7) years and 23.6 (0.4) kg/ > m2 respectively. Bearing in mind the location of the adults used in this study it would be interesting to know the skin colour of those with low <30ng/mL or <75nmol/L Does anyone know? It is well known that the darker the skin colour the longer exposure (up to ten times as long for the darkest hue) to sunshine is needed to obtain the same amount of Vit d produced in a white skin. If these were black skinned indiviuals then the approx 30hrs exposure would represent the equivalent of 3hrs exposure for a Caucasian skin and while 3hrs sun exposure should be adequate, three one hour sunbathing sessions a week is not excessive exposure and if it is occuring in a swimming pool/hot tub environment where the vitamin d produced on the surface of the skin is washed off before it can be absorbed this may account for some of the low level of synthesis. The highest concentration of 62ng/ml works out at 155 nmol/L which compared with the optimal of 50 ng/mL (125 nmol/L) is not particularly high. Hollis is arguing in http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=Abstra ctPlus&list_uids=17218096 that 100nmol/Lshould be regarded as being Vitamin d replete. < from concluson "When humans are sun (or dietary) replete, the vitamin D endocrine system will function in a fashion as do these other steroid synthetic pathways, not limited by substrate. Thus, the relationship between circulating vitamin D and 25(OH)D may represent what "normal" vitamin D status should be." The point we should take from this research is that 25-hydroxyvitamin D testing should become standard practice and everyone should know how near to optimal 50 ng/mL or 125nmol/L are. It's a pity in the UK it costs so much to get tested but I expect if everyone demanded a test twice yearly the price would come down as it would become econimically viable to purchase the technology to automate the test procedure. MarilynMann <mannm@comcast.net> wrote in part: >Additionally, as the >maximal 25(OH)D concentration produced by natural UV exposure appears >to be 60 ng/ml, it seems prudent to utilize this value as an upper >limit when prescribing vitamin D supplementation. So what does that translate into for supplementation levels during periods of good sun exposure? -- Jim Chinnis Warrenton, Virginia, USA jchinnis@alum.mit.edu > MarilynMann <m...@comcast.net> wrote in part: > >Additionally, as the > >maximal 25(OH)D concentration produced by natural UV exposure appears > >to be 60 ng/ml, it seems prudent to utilize this value as an upper > >limit when prescribing vitamin D supplementation. > So what does that translate into for supplementation levels during periods > of good sun exposure? http://www.ajcn.org/cgi/reprint/59/1/80 shows that a high dose of vitamin D (446-1147 IU/day) with high sun exposure in elderly women results in less than 30 ng/ml. -- Ron Ron Peterson <ron@shell.core.com> wrote in part: >> MarilynMann <m...@comcast.net> wrote in part: > [quoted text clipped - 9 lines] >vitamin D (446-1147 IU/day) with high sun exposure in elderly women >results in less than 30 ng/ml. Thanks. Hmmm. So ... if I were an elderly woman getting lots of sunshine, the supplementation limit would be in excess of about 2300 IU/day... All data points are welcome. -- Jim Chinnis Warrenton, Virginia, USA jchinnis@alum.mit.edu You may be aware of this already, but a good source of info on vitamin D research is the Vitamin D Council's website, www.vitamindcouncil.com. You can also sign up to have their newsletter e-mailed to you. Back issues are on the website. Marilyn > You may be aware of this already, but a good source of info on vitamin > D research is the Vitamin D Council's website,www.vitamindcouncil.com. > You can also sign up to have their newsletter e-mailed to you. Back > issues are on the website. That website claims chronic use of 40,000 IU of vitamin D shows signs of toxicity. -- Ron > Hmmm. So ... if I were an elderly woman getting lots of sunshine, the > supplementation limit would be in excess of about 2300 IU/day... > > All data points are welcome. > -- > Jim Chinnis Warrenton, Virginia, USA jchin...@alum.mit.edu http://www.ajcn.org/cgi/content/full/77/1/204 Shows Healthy men seem to use 3000-5000 IU cholecalciferol/d. This Risk assessment for vitamin D http://www.ajcn.org/cgi/content/full/85/1/6 presents a risk assessment based on relevant, well-designed human clinical trials of vitamin D. Collectively, the absence of toxicity in trials conducted in healthy adults that used vitamin D dose 250 µg/d (10 000 IU vitamin D3) supports the confident selection of this value as the Upper Limit. Effects of Above Average Summer Sun Exposure on Serum 25- Hydroxyvitamin D http://jcem.endojournals.org/cgi/content/abstract/87/11/4952?ijkey=83dc633578cae 00cb9f6a45978b5e666f298f527&keytype2=tf_ipsecsha Bearing in mind this research took place in Omaha, Nebraska Latitude 41 (roughly the same as Rome) says "our subjects' sun exposure was equivalent in 25(OH)D production to extended oral dosing with 70 µg/d vitamin D3 or, equivalently, 2800 IU/d Despite this input, at the late winter visit, 25(OH)D was less than 50 nmol/liter in 3 subjects and less than 75 nmol/liter in 15 subjects. It helps to increase your Vitamin D intake from sunshine if you take your clothes off. The idea that you can get sufficient vitamin D simply by walking to the car or from the car to office/shops is simply myth. If working outdoors all day in Ohmaha only produces on average 2800iu/d it's not surprising that 90% of the UK population are vitamin d insufficient and most remain so all year. http://www.ajcn.org/cgi/content/abstract/85/3/860 Hypovitaminosis D in British adults |
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