http://www.ncbi.nlm.nih.gov/entrez/q...=pubmed_DocSum

J Photochem Photobiol B.
2006 Dec 1; [Epub ahead of print]

Location and Vitamin D synthesis: Is the hypothesis validated by geophysical data?

Kimlin MG, Olds WJ, Moore MR.
Institute of Health and Biomedical Innovation, Faculty of Health, Queensland University of Technology, Kelvin Grove, Qld, 4059 Brisbane, Australia.

The literature reports strong correlations between UV exposure and latitude gradients of diseases. Evidence is emerging about the protective effects of UV exposure for cancer (breast, colo-rectal, prostate), autoimmune diseases (multiple sclerosis, type II diabetes) and even mental disorders, such as schizophrenia. For the first time, the available levels of vitamin D producing UV or "vitamin D UV" (determined from the previtamin D action spectrum) and erythemal (sunburning) UV from throughout the USA are measured and compared, using measurements from seven locations in the USA are measured and compared, using measurements from seven locations in the US EPA's high accuracy Brewer Spectrophotometer network.

The data contest longstanding beliefs on the location-dependence and latitude gradients of vitamin D UV. During eight months of the year centered around summer (March-October), for all sites (from 18 degrees N to 44 degrees N latitude) the level of vitamin D UV relative to erythemal UV was equal (within the 95% confidence interval of the mean level). Therefore, there was no measured latitude gradient of vitamin D UV during the majority of the year across the USA.

During the four cooler months (November-February), latitude strongly determines vitamin D UV. As latitude increases, the amount of vitamin D UV decreases dramatically, which may inhibit vitamin D synthesis in humans. Therefore, a larger dose of UV relative to erythemal UV is required to produce the same amount of vitamin D in a high latitude location. However, the data shows that at lower latitude locations (<25 degrees N), wintertime vitamin D UV levels are equal to summertime levels, and the message of increasing UV exposure during winter is irrelevant and may lead to excessive exposure. All results were confirmed by computer modeling, which was also used to generalize the conclusions for latitudes from 0 degrees to 70 degrees N.

The results of this paper will impact on research into latitudinal gradients of diseases. In particular, it may no longer be correct to assume vitamin D levels in populations follow significant latitude gradients for a large proportion of the year.

PMID: 17142054 [PubMed - as supplied by publisher]

This is very interesting data, Wannabe.

Living in one of the higher latitudes, I better increase my UV exposure. They didn't say, but I wonder if taking vit D supplements would suffice??

Thanks for posting.

Sally:

Can't remember what journal/articles I have read on the subject but for someone living at my latitude (northern Canada) and below (northern U.S.) they now recommend that an individual take 1000 mgs of Vit. D between October and June.

Unfortunately that is cost-inhibitive for many of us and in my area you can only get Vit. D in 400 mg. bottles. I did see Vit. D in 1000 mg. bottles in the states though.

Being on a fixed income one has to pick what works and since veggies and fruits are important to my daughter's health (and mine) my grocery money goes on those items, which are not cheap because they have to be trucked in.

If I could afford it, I would definitely consider taking that level of Vit. D, if for nothing else than the increase in energy during the dark cold winter months.