There is no magic in eating pumpkin seeds. Instead, its ingredients have been scientifically shown to hav good effects on prostate health.
Pumpkin seeds are rich in Zinc, the beneficial mineral in the prostate metabolism.
1 seed of pumpkin contains around 2.17 mg of Zinc. You need to get 20 mg of Zn from the foods/drinks you consume on daily basis.
So, you should not eat more than 8 pumpkin seeds per day.