CONTEXT: Public health authorities around the world recommend widely variable 
supplementation strategies for adults, whereas several professional 
organizations, including The Endocrine Society, recommend higher 
supplementation.
METHODS: We analyzed published randomized controlled clinical trials to define 
the optimal intake or vitamin D status for bone and extraskeletal health.
CONCLUSIONS: The extraskeletal effects of vitamin D are plausible as based on 
preclinical data and observational studies. However, apart from the beneficial 
effects of 800 IU/d of vitamin D3 for reduction of falls in the elderly, 
causality remains yet unproven in randomized controlled trials (RCTs). The 
greatest risk for cancer, infections, cardiovascular and metabolic diseases is 
associated with 25-hydroxyvitamin D (25OHD) levels below 20 ng/mL. There is 
ample evidence from RCTs that calcium and bone homeostasis, estimated from serum 
1,25-dihydroxyvitamin D and PTH, calcium absorption, or bone mass, can be 
normalized by 25OHD levels above 20 ng/mL. Moreover, vitamin D supplementation 
(800 IU/d) in combination with calcium can reduce fracture incidence by about 
20%. Such a dose will bring serum levels of 25OHD above 20 ng/mL in nearly all 
postmenopausal women. Based on calculations of the metabolic clearance of 25OHD, 
a daily intake of 500-700 IU of vitamin D3 is sufficient to maintain serum 25OHD 
levels of 20 ng/mL. Therefore, the recommendations for a daily intake of 
1500-2000 IU/d or serum 25OHD levels of 30 ng or higher for all adults or 
elderly subjects, as suggested by The Endocrine Society Task Force, are 
premature. Fortunately, ongoing RCTs will help to guide us to solve this 
important public health question.