I didn't know about that one. What made me suspect sleep was a few studies showing that a lack of sleep has a negative effect on various hormones: http://www.

I didn't know about that one. What made me suspect sleep was a few studies showing that a lack of sleep has a negative effect on various hormones: http://www.ncbi.nlm.nih.gov/pubmed/22844441 http://www.ncbi.nlm.nih.gov/pubmed/22844441 http://www.ncbi.nlm.nih.gov/pubmed/22787499 http://www.ncbi.nlm.nih.gov/pubmed/22787499 http://www.ncbi.nlm.nih.gov/pubmed/19955752 http://www.ncbi.nlm.nih.gov/pubmed/19955752 http://www.ncbi.nlm.nih.gov/pubmed/10543671 http://www.ncbi.nlm.nih.gov/pubmed/10543671 http://www.ncbi.nlm.nih.gov/pubmed/23078578 http://www.ncbi.nlm.nih.gov/pubmed/23078578 I found a couple studies on acne that mentions lack of sleep: http://www.ncbi.nlm.nih.gov/pubmed/18348416 http://www.ncbi.nlm.nih.gov/pubmed/18348416 http://www.ncbi.nlm.nih.gov/pubmed/21595660 http://www.ncbi.nlm.nih.gov/pubmed/21595660