As a source of Vitamin D3, whole body UV (sunshine) between 10 am and 1 pm for 20 minutes will give a D3 equivalent to oral dosing with 10,000 iu vitamin D3 (cholecalciferol). This is a rough estimate - it assumes you are outside only between March and October if north of 37 degrees latitude, and that you are unclothed and have average skin pigmentation where your minimal erythemal dose (MED) is 20 minutes. Black persons may need 5-6 times the exposure for the same dose. There is simply no natural food source that can compare to the Paleolithic one of sunlight.
How much do you need and what is deficient?
Referencing the classical effects of D we might define insufficiency at less than 20 ng/ml and severe deficiency at 10 ng/ml. Current RDAs of 400 iu/day are based on avoiding rickets and were made before there was recognition of the other important effects of D. The dose-response curve for serum levels is highly non-linear, with each 5 ng/ml increment in serum levels requiring a larger increase in daily intake. Even 400 iu/day has been shown to be ineffective in treating osteoporosis. The non-classical effects of D seem to require larger levels to ensure health. Using a few facts we can come up with a more modern recommendation that is safe and reflects a more complete understanding of the importance of vitamin D.
1) The level of 25(OH)D at which most dietary calcium intake is adequate (absorption is maximized) is 50 ng/ml
2) The level of 25(OH)D that optimizes fracture prevention is about 40 ng/ml
3) The level that causes PTH levels to plateau at a minimum (ensures no secondary hyperparathyroidism) is 40 ng/ml
4) The level of oral D3 intake required to ensure a level of 40 ng/ml in most people is 4000 iu/day
5) The highest reported level of oral intake that has never been associated with a case of hypercalcemia due to hypervitaminosis D is 10,000 iu/day
Using the above numbers most of us who are not lifeguards have D3 insufficiency if not deficiency.
Here are some approaches to Vitamin D replaclement I think are reasonable:
If you can get adequate sunlight at midday, say, sitting outside at lunchtime with 25% of your skin exposed for an hour, and your latitude and the season allow enough UV, you can use that as your source. Am I concerned about skin cancer or wrinkles? Iíll cover that in an upcoming post but basically I think sunning without burning is fine. I suspect what really trashes your skin are PUFAs and cigarettes, not the sun. If you really worry about wrinkling, wear a broad-brimmed hat and get the sun on your arms and shoulders. As an aside, my MED is now more than twice what it used to be since I eliminated plant oils- others have reported less burning (inflammation) with less O-6 PUFAs in the diet as well.
If you are like most people most of the time, UV as your sole source will not be practical. Ideally, get your 25(OH)D level and ionized calcium measured, and if it is less than 40 ng/ml, take 8000 iu/day for two months and measure it again. If 40-50, take 6000 iu/day. Any day you get full-dose sun, skip the oral dose. If still below 50 ng/ml, add 2000 iu/day with each two month increment until your interval two month reading is above 50 ng/ml. Once you are stabilized above 50ng/ml, check your levels annually
If you donít want to medicalize your diet this much, you could take 4000 iu/day every day. You could skip the pills on days with sun, or not. You will not get hypercalcemic on this unless you already have primary hyperparathyroidism or some other confounding disease. I would recommend 25 (OH)D levels at least yearly, though.
D2 from plants may well be equally efficacious as D3, but I canít think of any reason to avoid the D3 we were designed to use as animals. Oil based capsules with 2000 iu of D3 each are economical, easy to swallow and more reliably absorbed than the dry pill form. Carlsonís is a good brand.