Enhanced Growth of the Adult Penis With Vitamin D 3: https://www.researchgate.net/publication/322071346_Enhanced_Growth_of_the_Adult_Penis_With_Vitamin_D_3

Abstract: Fourteen adult men volunteered to participate in an experiment to evaluate the potential for penile growth as a result of taking 50,000 units of vitamin D 3 and 100 mcg of vitamin K 2 daily. Penis length increased an average of 0.46 inches and circumference increased an average of 0.523 inches, both statistically significant. These results are comparable to those obtained with use of a vacuum pump or with surgical augmentation. We suggest that men interested in penis augmentation consider this much simpler and safer approach when they are interested in penis enlargement.

The role of vitamin D supplementation on erectile function: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5503426/

Does vitamin D deficiency contribute to erectile dysfunction?: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3427191/