The problem with pointing to retrospective observational studies as basis to show that vitamin D is associated with increased risk in bad health outcomes is that when it comes to vitamin D, there are literally thousands of observational studies that show, the higher your vitamin D blood level (0-60 ng/ml), the better the health outcome across a broad spectrum of diseases. These studies receive a lot of media attention, but not nearly as much attention the very rare "vitamin D is bad" finding receives. Much to our organization's disappointment, when the latter type of news story breaks, some doctors are quick to pick them up, despite not having any thorough understanding or background on the literature of the topic
There is very strong evidence that show that vitamin D plays a role in preventing cancer, including pancreatic cancer. To say the opposite, as Dr. McDougall does, would leave anyone familiar with the literature dumbfounded. In a study just published this month in the journal of
Cancer Epidemiology, Biomarkers and Prevention found that, "Among participants in five large prospective cohorts, higher plasma levels of 25(OH)D were associated with a lower risk for pancreatic cancer."
http://www.ncbi.nlm.nih.gov/pubmed/22086883The only randomized controlled trial looking at vitamin D supplementation and cancer outcomes using a somewhat significant dose of vitamin D (1100 IU, still very low dose) to date found a 77% reduction in all-type cancer incidence in comparing vitamin D to placebo.
http://www.ncbi.nlm.nih.gov/pubmed/17556697Similar evidence from observational studies exists for an association between high vitamin D levels and lower cardiovascular disease incidence. From the
Archives of Internal Medicine: "Low 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D levels are independently associated with all-cause and cardiovascular mortality. A causal relationship has yet to be proved by intervention trials using vitamin D." Note the last sentence. We really need randomized controlled trials to tell us whether vitamin D plays a beneficial role in cardiovascular disease, but there is a ton of observational literature that shows potential benefit in vitamin D for CVD outcomes. To say the opposite, again, is dumbfounding.
Vascular calcification? Again, studies show that vitamin D has an inverse relationship with coronary artery calcification. "In conclusion, lower 25-hydroxyvitamin D concentrations associate with increased risk for incident coronary artery calcification."
http://www.ncbi.nlm.nih.gov/pubmed/19443637Renal stones? No study has found vitamin D, independent of high calcium supplementation, to increase the incidence of kidney stones.
As far as all-cause mortality goes, there are many observational studies that show a linear relationship between high vitamin D levels and lowered risk of all-cause mortality. There are a couple of "u-shaped curves" that show a "sweet spot" for vitamin D, which is what you would expect from a fat-soluble vitamin and prohormone. This is another conversation, but we believe any objective look at current literature would tell you, you probably need to supplement with vitamin D, you probably aren't getting enough sun exposure with your 21st century lifestyle.
Regards,
Brant Cebulla
Vitamin D Council
[email protected]