I was working on a retort to Icko, when I found a dandy article paleo-friendly WAPF leader Chris Masterjohn wrote about the ideal blood levels of vitamin D. He claims that we know that Vitamin D levels should be at least 30 to 35 ng/ml, but we don't know much more than that. Higher may be better; higher may be worse. But we don't really have good science telling us either way. The almost universal recommendation seems to be 50 ng/ml is a good place to be, but they suggest a little higher is probably better. My brother's naturopath informed him that his level of 75 ng/ml could be improved upon. Doctor JE Williams suggests that we should shoot for 100 ng/ml. What is a man to make of all this nonsense?
I was part of the group that was hired by the federal government to do the Vitamin D systematic review. It is a beastly 420 page report, available for free here.
In summary, there are 200-300 vitamin D trials that have been conducted. Evidence is conflicting for most outcomes (bone, cardiometabolic, cancer). Adverse events are few and far between.
Because the data is not complete by any stretch of the imagination, I would listen to King of Vitamin D, Michael Hollick: "Humans need 1,000 IU each day, or to be exposed to sunlight. Five to ten minutes, arms and legs, three times a week, is adequate." Extra may be fine, but no reason to go above what you would naturally get from the sun (>60 ng/ml).
My advice would be to look at people who spend a lot of time in the sun in an area that they are naturally adapted for, perhaps african americans in africa and native americans in California. Or if the funding were available, naturally living hunger gatherer tribes would make fine testing subjects. Make sure they do not use sunscreen or supplements, and then see what their natural vit D levels are. Remember that the body will shut of D production from the sun when it no longer wants any more. What we need to do is see when the body stops production for people with natural levels of sun exposure in their natural environments. Assuming that the levels are similar across genetics (and they may not be), then we would probably have a good idea of what our body wants as far as D levels, and then we can shoot for that. Of course, preferred levels may be altered by diet and other factors, and for all we know, the body may even alter its production preferences based on myriad factors and feedback mechanisms, but personally, I would start with on the ground natural observations first. I wonder if anything like that has yet been done. ONe would think it might be cheaper than other kinds of studies as all that would be needed would be a blood test and fill out some questionaires. The hardest part would finding people in their native environments who do not sit in offices all day.
I thought that one of the ideas was that at 50ng/ml and above, breast milk is replete with vitamin D. Another interesting factoid is that you can easily get 10,000-20,000iu from one session in the sun. Not sure that we know what the 'optimum' level is or whether there are possible downsides to supplementing versus sun exposure. I try to get as much as I can can from the sun, but I also take 5-10k/day, depending on the time of year. Just had my fist test and it was 73ng/ml. I almost never get sick. And when I do, its mild and over quickly, compared to the other people in my house who are usually sick in the same time frame. (They don't take the D)
Personally, I think over 50 is fine - 60 might be slightly better. Biologically, what would having more do? If your cells have all they need to perform whatever function they desire, I don't see why higher would be better. The only remaining question is how much would satisfy the cells completely. Perhaps having some extra is a good thing. And there doesn't appear to be any toxic side effects (at these doses), unlike vitamin A.
This post by Dr. Harris is also excellent:
White people in tropical sun top out around 60ng/ml. I wouldn't go higher than the maximum that nature has picked. I agree that there is no evidence of acute toxicity at even higher amounts, but that is not an argument for why these higher levels are healthy. Most evidence suggests a sweet spot around 40-50ng/ml.
after tinkering around with several different dosages and failing to get higher than 60nmol (24ng) even with 10'000IU/d, my newest (personal) approach is this: - each person has a different supplemental need for D3 and dosages may vary very widely - each person may have a different "optimal" target range depending on genetics and other conditions (receptor variations, autoimmunity, chronic infections etc) - the best indicator for optimal range is how you feel and perform (=mood, focus, energy) - as long as these indicators improve, increase the dosage - when reaching 20'000IU/d, be sure to check calcium and 1.25-OH to make sure you're not in a toxic state. if not, you may increase dosage even further - be sure to not be deficient in K1/K2, zinc and magnesium. supplement if needed - after indicators don't improve any more, or the neurotransmitter boost that comes with higher dosages gets too strong, lower dosage step by step until indicators worsen again - your optimal dosage is where health indicators are best, and don't improve anymore with a higher dosage - if you're over 40, you don't need to adjust the dosage for exposure to sunshine - monitor D3 and calcium levels periodically