What is a major effect of human growth hormone (HGH)?

Human growth hormone (HGH) plays a significant role in growth, body composition, cell repair, and metabolism. One of its primary effects is an increase in muscle mass and a reduction in body fat. HGH stimulates the production of insulin-like growth factor 1 (IGF-1), which in turn promotes muscle growth and regeneration.

Additionally, HGH enhances protein synthesis, which is crucial for muscle repair and growth following physical activity. It also promotes the break down of fats to provide energy, contributing to decreased body fat and improved body composition. These properties make HGH particularly relevant in discussions about athletic performance and body composition, as athletes often seek to enhance muscle growth while reducing fat.

The other options do not accurately reflect the well-documented effects of HGH. For instance, decreasing muscle mass or reducing mental alertness is contrary to the established benefits of HGH. While HGH does play a role in expanding blood vessels and enhancing blood flow, its primary recognized outcomes are related to muscle growth and fat metabolism, making the increase in muscle mass and decrease in body fat the most accurate summary of its major effects.