Growth hormone is a naturally occurring substance secreted by the brain that helps guide growth in childhood and maintain muscle mass during adulthood.

FORBES: Sweet syringe of youth

New Scientist magazine reports that the researchers, led by Mark Tuszynski, of the University of California, San Diego, believe a substance called nerve growth factor (NGF) can prevent the death of cells in the brain known as cholinergenic neurons, and stimulate new connections between the cells.

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They have identified tiny spheres that regulate the formation and organisation of tooth enamel by controlling the substance's crystalline growth.

BBC: By BBC News Online Science Editor Dr David Whitehouse

Overuse of vitamin D, a substance that promotes the growth of bone and teeth in children, can be particularly toxic, as can overuse of the mineral iron by older adults.

CNN: ASIANOW - TIME Asia

The VEGF gene is so-called because it controls production of a substance known as vascular endothelial growth factor.

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Ms. KATIE COURIC (Host, "60 Minutes"): For the record, have you ever used steroids, human growth hormone, or any other performance-enhancing substance?

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In the meantime the Food and Drug Administration has only approved growth hormone for treating patients whose bodies can't produce the substance because of injury or disease, but physicians are allowed to prescribe it if they see fit.

FORBES: Sweet Syringe of Youth

In the meantime the U.S. Food and Drug Administration has approved growth hormone only for treating patients whose bodies can't produce the substance because of injury or disease.

FORBES: Sweet syringe of youth