July 27, 2010
Vitamin D And Disease Risks
Jane Brody of the New York Times takes a look at the evidence for benefits from raising blood vitamin D levels.
“As a species, we do not get as much sun exposure as we used to, and dietary sources of vitamin D are minimal,” Dr. Edward Giovannucci, nutrition researcher at the Harvard School of Public Health, wrote in The Archives of Internal Medicine. Previtamin D forms in sun-exposed skin, and 10 to 15 percent of the previtamin is immediately converted to vitamin D, the form found in supplements. Vitamin D, in turn, is changed in the liver to 25-hydroxyvitamin D, the main circulating form. Finally, the kidneys convert 25-hydroxyvitamin D into the nutrient’s biologically active form, 1,25-dihydroxyvitamin D, also known as vitamin D hormone.
A person’s vitamin D level is measured in the blood as 25-hydroxyvitamin D, considered the best indicator of sufficiency. A recent study showed that maximum bone density is achieved when the blood serum level of 25-hydroxyvitamin D reaches 40 nanograms per milliliter or more.
“Throughout most of human evolution,” Dr. Giovannucci wrote, “when the vitamin D system was developing, the ‘natural’ level of 25-hydroxyvitamin D was probably around 50 nanograms per milliliter or higher. In modern societies, few people attain such high levels.”
Note Giovannucci's reference to human evolution as relevant to discussions about human dietary needs. The Paleo Diet approach to looking at human nutrition is becoming mainstream. You can find knowledgeable writers on nutrition such as Stephan Guyenet basically taking an anthropological approach to identifying appropriate foods including the use of isotope ratios in predecessors to modern humans to discover how much of different food types they ate.
Brody also quotes noted vitamin D researcher Michael Holick. Worth a read to hear what he has to say about disease risks that are boosted by not getting enough vitamin D.
Holick recommends blood concentrations of 25-hydroxyvitamin D above 80 nmol/L, (approximately 30 ng/mL ) that's double the amount you need for max bone health. As this is the ONLY proven clinical end point for vitamin D Holick doesn't know what he is talking about.
A systematic review of the association between common single nucleotide polymorphisms and 25-hydroxyvitamin D concentrations
"We speculate that recently identified U-shaped relationships between 25OHD concentrations and disease outcomes (i.e. increased risk at both high and low concentrations) may reflect a mixture of genotype-defined subgroups."
'Genetics to Blame for Vitamin D Deficiency?'
"Researchers conducted a genome-wide association study (,a href="http://www.ncbi.nlm.nih.gov/pubmed/20541252">Common genetic determinants of vitamin D insufficiency: a genome-wide association study) that involved almost 34,000 people of European descent from 15 different studies. They used radioimmunoassay and mass spectrometry to determine vitamin D concentrations and found that variants at three genetic sites, or "loci," were significantly associated with vitamin D concentrations. The presence of harmful alleles at three "loci" more than doubled the risk of Vitamin D insufficiency."
Maybe non-whites are the ones who benefit from doubling their vitamin D levels ? Nope - Vitamin D, Adiposity, and Calcified Atherosclerotic Plaque in African-Americans "positive associations exist between 25-hydroxyvitamin D and aorta and carotid artery CP in African-Americans"
Many people are naturally low in vitamin D, forcing vitamin D levels up by taking supplements can only do harm. If you think you can improve health by conforming to the advice of Holick or - God forbid - that of Hollis, Cannel & Co at the vitamin D 'Council' who recommend (>50ng/ml) then you are in for an unpleasant surprise.
Vitamin D and homeostasis
Mad dogs and ....
"For the study, Reid's team did a meta-analysis of 11 randomized, controlled trials involving 11,921 people. In other words, the researchers reviewed already published studies and teased out data on any connection between calcium supplements and heart attacks....He and other researchers noted that the study had certain limitations, including excluding studies in which participants took both vitamin D and calcium supplements, and added that some of the trials they reviewed did not collect data on heart problems in a standardized manner."
They specifically excluded studies in which participants took both vitamin D and calcium supplements!