Professor Joan Lappe of Creighton University has written an up to date review article on vitamin D that serves as a good primer for anyone just awakened to the “vitamin D revolution.” It is free to download or read online.
While she doesn’t come right out and say it, her citations imply clearly that more than 2,000 IU/day are needed for the maximum benefit of vitamin D, pointing out for example that levels of 53 ng/ml would prevent 50% of breast cancer. Levels of 53 ng/ml require about 5,000 IU per day unless you are obese, which may require you to take more.
Keep in mind that body weight is only one of the factors that determine how much a given dose will increase your vitamin D levels. The main factor appears to be genetic. That is, you inherit a vitamin D metabolic system and some systems are very good at increasing 25(OH)D levels and others are not so good at doing so. When low 25(OH)D levels persist after taking say 10,000 IU per day, many people assume it is poor absorption, and it may be.
Gastric bypass surgery and intestinal disease impair absorption, while medications, such as glucocorticoids and anticonvulsants, can lower vitamin D levels. Few people know that low taurine levels also decrease vitamin D absorption, at least in infants.
Another, almost completely un-researched area is “metabolic clearance,” or how much you “use up” when you are ill or have surgery or exercise vigorously. To my knowledge, only one study addresses the subject, in knee replacement, and it found the procedure used up lots of vitamin D. What about influenza, or heart failure, or liver disease, etc.? How much does that use up? No one knows, but keep in mind that vitamin D is not recycled; it is a one way street from vitamin D to 25(OH)D to activated vitamin D to 1,24,25-vitamin D to calcitroic acid to urinary execration.
To give you an idea of just how limited the research is in this area, take kidney disease patients who require activated vitamin D to maintain their serum calcium. Well, one of the things activated vitamin D does is ramp up the enzyme that destroys vitamin D, so what is the effect of activated vitamin D on the 25(OH)D of kidney patients? No one knows.
If you are one of those people whose vitamin D levels will not go above 40 ng/ml, even on 10,000 units per day, and you won’t use sunlight or sunbeds, just keep increasing the dose up to 20,000 IU per day. If that does not work, buy some coconut oil on the internet and add the contents of two 5,000 IU capsules of vitamin D to a tablespoon of coconut oil. Mix it well and then rub it into your skin every day, and see if that raises your vitamin D level.
If it does not, then your genetics may be keeping your vitamin D level low, or you may have a disease using up your vitamin D. Just keep upping your oral dose until you get a level of 50 ng/ml. However, if you are one of these few people who have to take mega doses of vitamin D, you have to continue to frequently monitor your vitamin D levels. If you take 10,000 IU/day or more, I urge you to get your 25(OH)D tested regularly.