Where did the Vitamin D Council get its recommendation that adults take 5,000 IU/day of vitamin D3 for the rest of their life? The Institute of Medicine’s Food and Nutrition Board say 600 IU/day is enough for adults and the Endocrine Society says 2,000 IU/day is enough for most adults.
We think the safest thing to do while all the research is going on is to maintain natural vitamin D levels. By natural, we mean those levels obtained by those with natural sun exposure, such as lifeguards, some roofers and gardeners, and others who work in the sun and expose a lot of skin to sunshine. This is how our ancestors behaved throughout our evolutionary history.
The best study that examined the vitamin D levels of people who get plenty of sun exposure was published last year. Researchers discovered that free-living hunter gatherers living around the African equator (where humans evolved) have average vitamin D levels of 46 ng/ml (115 nmol/L).
Luxwolda MF, Kuipers RS, Kema IP, Dijck-Brouwer DA, Muskiet FA. Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l. Br J Nutr. 2012 Nov 14;108(9):1557-61.
Most people will not have their blood tested unless their doctor recommends it. So we needed a recommended dose that:
When we decided on a recommendation with the four goals above in mind, we also had to take into account body weight. Besides genetics, body weight is the single biggest determinate of vitamin D levels. The more you weigh, the more vitamin D you need to take.
Professor Robert Heaney of Creighton University details in the study below just how high vitamin D supplementation/input needs to be to reach the vitamin D level goals above.
Drincic AT, Armas LA, Van Diest EE, Heaney RP. Volumetric dilution, rather than sequestration best explains the low vitamin D status of obesity. Obesity (Silver Spring). 2012 Jul;20(7):1444-8. doi: 10.1038/oby.2011.404.
Together with his coauthors, Professor Heaney stated that for a normal weight adult, 5,000 IU/day of total input was needed to obtain a vitamin D level of 40 ng/ml. Of course the final vitamin D level obtained by any dose depends on baseline level, sun exposure and genetics. But he was speaking of the average adult.
For those who want a more careful calculation, he stated his data showed that 70-80 IU/day/kg of body weight total input is needed to obtain a 25(OH)D of 40 ng/ml. That works out to about 35 IU/day/pound. So a 100 pound woman would need 3,500 IU/day of total input but a 300 pound lineman would need 10,500 IU/day. Keep in mind this is total input, which includes sunlight, diet and supplements.
Taking all these factors into account, we conclude a recommendation of 5,000 IU/day is about right for the average adult.