Hi jc,
Your posts are always great, and have provided some of my favorite info.
Re: Are vitamin D supplements beneficial, or only sun?
Here's a double blind randomized controlled study, where 1100IU of vitamin D supplements, plus calcium, reduced cancer incidence 50% over 4 years, for post menopausal women. WoW !!
http://www.ncbi.nlm.nih.gov/pubmed/17556697 (Free full text:
http://www.ajcn.org/content/85/6/1586.abstract )
An amazing sentence in the abstract:
In multiple logistic regression models, both treatment and serum 25-hydroxyvitamin D concentrations were significant, independent predictors of cancer risk.What this means, is that the blood (serum) level of vitamin D was an independent predictor of cancer risk, in ADDITION to whether the person was taking the 1100 IU of vitamin D supplement. This means that if many people all take 1100 IU of vitamin D, there is a great deal of variation in the resulting blood level. Saying the same thing in a more statistical manner, there is a weak correlation between supplement level, and blood level of vitamin D. (We know from other sources that there is a VERY weak correlation between sunlight exposure and blood vitamin D level.)
From this, we can conclude, with ALMOST certainty, two things. 1) Yes, to answer your question, vitamin D supplements improve health. 2) People should get a blood level test for vitamin D, and decide whether to supplement, and how much, based on the blood test.
(I say ALMOST certainty, since the study was not large, and was statistically significant, but we would like to see the study repeated.)
This study suggested that ideal blood vitamin D levels are 35 to 55. Dr. Fuhrman's experience is that most people need 1000 to 2000 IU supplement, to achieve these levels. A few people need no supplement, and a few people need much more.
Below 30, cancer incidence increased. Above 55, possibly cancer incidence increased. We would like to see more studies, to explore the upper limit of vitamin D safety. Another study showed heart disease, diabetes, obesity, etc increased, below 30. (This study did not evaluate supplements, but evaluated blood levels.)
http://download.journals.elsevierhealth.com/pdfs/journals/0002-9149/PIIS0002914910011318.pdf Many studies show that supplements are valuable, for reducing hip fractures, etc. Case histories show that supplements improve or cure many people's issues.
Best regards, EngineerGuy