In 2006, three significant research papers were published in peer-reviewed medical journals by different respected authors, each coming to the same conclusion. You need more vitamin D than the recommended amount for adults of 400 IU per day – actually much more! Most calcium supplements and multi-vitamins are formulated to this AI (Adequate Intake) level. Listen to what the new research is showing.
Bischoff-Ferrari's article in The American Journal of Clinical Nutrition reviewed the current literature and found that for bone mineral density (BMD) and fracture risk reduction, lower-extremity function, dental health, and colorectal cancer prevention the best serum concentration of 25 hydroxy vitamin D are at 90 - 100nmol/L. (Vitamin D that is synthesized in your skin becomes 25 hydroxy vitamin D circulating in your blood stream. This is the best measurement of the level of vitamin D you have available for use in your various tissues). The Bischoff-Ferrari team found that healthy outdoor workers have 135 - 163 nmol/L. The first sign of D toxicity begins at 220 nmol/L.
He recommends 2000 IU/day as a new safe RDA to bring 97% of the population to 90-100 nmol/L. To bring concentrations in 50% of population up to a conservative 75nmol/L, he recommends adult intake of 1000 IU/day. His conclusion states "a large majority of the US population could benefit from vitamin D supplementation."
A second significant article by one of the top bone health researchers in the world, Robert Heaney published in the Journal of Nutrition, says "Available data on metabolic utilization of vitamin D3 indicate a total daily requirement of approximately 4000 international units or twice the current tolerable upper intake level (UL)... Estimates of the population distribution of serum 25 hydroxy vitamin D values, coupled with available dose-response data, indicate that it would require input of an additional 2600 iu/d (65 microg/d) of oral vitamin D3 to ensure that 97.5% of older women have 25 hydroxy vitamin D values at or above desirable levels." Dr. Heaney's article was addressing older women, so the amounts needed for younger adults is generally less.
A third comprehensive 2006 article published in Mayo Clinic Proceedings by Michael Holick concludes 400 IU per day should represent a minimum for vitamin D supplementation rather than a recommended daily amount. Vitamin D toxicity has not been reported from long-term exposure to sunlight1,2 and has only been observed from dietary intake when daily doses exceed 10,000 IU.3 Doses of 4000 IU/d for 3 months and 50,000 IU/wk for 2 months have been administered without toxicity.
References
1. Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr. 2004;79(3):362-371. (PubMed)
2. Guyton KZ, Kensler TW, Posner GH. Vitamin D and vitamin D analogs as cancer chemopreventive agents. Nutr Rev. 2003;61(7):227-238. (PubMed)
3. http://dietary-supplements.info.nih.gov/factsheets/vitamind.asp