11.   Charles Czeisler of Harvard Medical School in Boston knew that melatonin pills seem to improve sleep only for people whose bodies are not producing normal levels of melatonin.

12.   Created in the testicles, it tells the pituitary gland that the body has produced enough FSH, and the gland responds by shutting down sperm production.

13.   Cystic fibrosis is a genetic disease that causes the body to produce an abnormally thick, sticky mucus, causing life-threatening lung infections.

14.   Diets that restrict all carbohydrates cause the body to produce compounds known as ketones that accumulate in the blood and must be removed.

15.   Despite an assiduous search, scientists have found only a half-dozen people in the world whose bodies produce no leptin.

16.   Eggs contain dietary cholesterol, which affects the type of serum cholesterol the body produces.

17.   Endocrinologists have concluded that the stress of competition in these events causes the body to produce high levels of growth hormone.

18.   Forced to utilize fat for fuel instead of sugar, the body produces byproducts called ketones.

19.   He discourages them, because teenage bodies produce an abundance of hormones.