Both are human studies. The doses used were not that high either - only 250mg a day in the first study and 1200mg per square meter of body surface area in the second one.
http://www.ncbi.nlm.nih.gov/pubmed/1286017/
http://www.ncbi.nlm.nih.gov/pubmed/16233932/
The second study would equate to 1,500mg - 2,000mg of niacinamide daily for most people, which matches well this animal study I posted earlier:
viewtopic.php?f=75&t=4948
http://www.ncbi.nlm.nih.gov/pubmed/1286017/
http://www.ncbi.nlm.nih.gov/pubmed/16233932/
The second study would equate to 1,500mg - 2,000mg of niacinamide daily for most people, which matches well this animal study I posted earlier:
viewtopic.php?f=75&t=4948