Who needs more vitamin D, a 250lb fit man who has 12 percent total body fat or a 250lb obese man who has 50 percent total body fat?
We know vitamin D is a fat-soluble vitamin and another one of these “common sense” theories that sounds good have led most of us to respond that the 250lb obese man needs more vitamin D because body fat acts as a “sink,” collecting fat-soluble vitamins.
Leave it to Professor Robert Heaney’s group to see the light (although Professor Reinhold Vieth wrote the same thing several years ago in a textbook). The answer is — they both need the same amount. Using mathematical models that are beyond my psychiatric training, Dr. Andjela Drincic and colleagues at Creighton University recently wrote a beautiful paper that definitively answered the question.
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 Jan 19. doi: 10.1038/oby.2011.404.
Therefore, muscle and fat may well act the same when it comes to storing vitamin D for future use. When you try to figure out how much vitamin D someone needs, forget the “fat sink” theory, as sensible as it sounds, and keep in mind total body weight. However, also keep in mind the obese man may have lower levels to begin with, as obese persons may typically have lifestyles that are void of full body sun exposure.
Finally, I am comforted by the authors’ calculation of vitamin D requirements. They cite data that show, if you want the average person to have a level of 40 ng/ml, that person needs 70-80 IU/kg/day. If you do the math, the 250 pound man would need 7-8,000 IU/day from all sources, while a 125 pound woman would need 3,500-4,000 IU/day from all sources. It is difficult to make a general recommendation with vitamin D for adults because you don’t want to get too complicated. That’s why our almost 10-year-old recommendation is simply 5,000 IU/day, which serves well for the majority of adults.