Remember how I hypothesized about vitamin D’s ability to prioritize which organ gets vitamin D when levels are less than 40 ng/ml? Think of a mountain with a lake at the top and many streams coming out of the lake to really important gene pools below, and then streams coming out of those to longer-latency (diseases way in the future) pools down, etc. Think of about thousands of total pools on that mountain, some high up and some low down, for the genes in the 38 tissues vitamin D regulates. The gene pools low down do not get much vitamin D unless the lake and upper pools are full. A recent study linked 3,000, not 2,000, human genes to vitamin D, so we are talking a lot of pools.
Ramagopalan SV, Heger A, Berlanga AJ, Maugeri NJ, Lincoln MR, Burrell A, Handunnetthi L, Handel AE, Disanto G, Orton SM, Watson CT, Morahan JM, Giovannoni G, Ponting CP, Ebers GC, Knight JC. A ChIP-seq defined genome-wide map of vitamin D receptor binding: associations with disease and evolution. Genome Res. 2010 Oct;20(10):1352-60. Epub 2010 Aug 24. PubMed PMID: 20736230; PubMed Central PMCID: PMC2945184.
The topmost lake is a “maintain blood calcium” lake. When reserves are low, like 20 ng/ml, the streams will begin to dry up as the body conserves all its vitamin D for the essential maintain blood calcium function. In addition, I suspect the cathelicidin (natural broad-spectrum antimicrobials used to fight serious infections) pool is above the prevent cancer pool for obvious reasons. I suspect the lowest pool will only be filled when vitamin D levels are over 50 ng/ml, but now we have evidence that one of the pools requires 40 ng/ml to start getting full.
Are we finding that one of the lowest pools has to do with type-2 diabetes? Dr. Pamela von Hurst and her colleagues at Massey University in New Zealand, conducted a randomized trial of 4,000 IU/day of vitamin D on 81 women and discovered that levels of 40 are better than levels of 30 in reducing insulin resistance. Notice again please, this is a randomized controlled trial.
von Hurst PR, Stonehouse W, Coad J. Vitamin D supplementation reduces insulin resistance in South Asian women living in New Zealand who are insulin resistant and vitamin D deficient – a randomised, placebo-controlled trial. Br J Nutr. 2010 Feb;103(4):549-55..
Indeed, their data did not have enough women with vitamin D levels of 50 ng/ml to know, but the improvements in insulin resistance showed no signs of stopping at 40 ng/ml, so we do not know when this pool is full. It may be full only at 40 ng/ml. Also, it took 4,000 IU/day for six months to get mean levels from 11 ng/ml to 32 ng/ml, about what you would expect in very deficient subjects with lots of empty pools.
The authors wrote,
“The findings provide further evidence for an increase in the recommended adequate levels of 25(OH)D from 20 to 30 ng/ml.”
However, her own data seemed to show that 40 ng/ml was better than 30 ng/ml, so she must have gotten nervous that 40 ng/ml might have been more beneficial.
One more thing, she reviewed diabetes papers showing vitamin D’s efficacy is better when given as daily doses, instead of weekly, monthly, or, in some cases, yearly doses. She quoted a paper in which a single dose of 300,000 IU worsened diabetes. For 2 million years, we got our vitamin D daily and that is how you should take it.