I get many letters about vitamin D absorption. “Should I take it with food?” “It is a fat soluble vitamin, so shouldn’t I take it with fat?” “Should I take it with a meal?” “Is it absorbed if I take it on an empty stomach?”
The answer to these questions is generally that it does not matter. Vitamin D is passively absorbed in the lower part of the small intestine (the jejunum and ileum), at least in rats. Surprisingly, one study found that absorption with a very high fat diet decreased vitamin D absorption in rats by 30%.
One human study of 25,000 IU as a single dose found that absorption was the same if scientists gave it with corn oil, whole milk, or fat free milk. Another study found that absorption of the powdered version was the same as vitamin D in oil. Another found vitamin D in oil was better than powdered but the difference between absorption rates was minuscule.
The latest addition to absorption studies came out of Tufts University in Boston. The authors, led by Dr. Sathit Niramitmahapanya, found that monounsaturated fats, like those found in beef and some oils, especially olive oil, was associated with better (that’s right better) absorption than vitamin D given with fish oils, but again the differences were not striking.
Niramitmahapanya S, Harris SS, Dawson-Hughes B. Type of dietary fat is associated with the 25-hydroxyvitamin d3 increment in response to vitamin d supplementation. J Clin Endocrinol Metab. 2011 Oct;96(10):3170-4.
The fact is that the studies are so conflicting, and the 25(OH)D measurement techniques are so variable, that it simply does not matter if you take vitamin D in oil or as a powder, it does not matter if you take food with your vitamin D, or on an empty stomach. What matter is that you take enough so that you obtain vitamin D levels of 50 -60 ng/ml. This means you are no longer suffering from substrate starvation (your vitamin D system has all the vitamin D it needs for all of its many uses and is beginning to store some vitamin D for the future).
Remember, if you have trouble getting your doctor to order the test, or if your insurance does not pay for it, or if your co-pays and deductibles are too high, or if your doctor keeps saying 600 IU/day is enough, or if he says levels of 30 ng/ml is fine, the Vitamin D Council has an in-home vitamin D testing service. You can measure your vitamin D levels at home via ZRT’s finger prick test that requires a little blood on a blotter paper. See our “Testing for vitamin D” page to find out more about the in-home vitamin D test.