Which condition is characterized by weight gain and decreased heart rate in adults?

The condition characterized by weight gain and decreased heart rate in adults is hypothyroidism. This condition occurs when the thyroid gland fails to produce enough thyroid hormones, which are critical for regulating metabolism, energy levels, and overall body functions.

In hypothyroidism, the reduced levels of these hormones lead to a slower metabolism, resulting in weight gain despite normal or decreased food intake. Additionally, the slowed metabolic rate can cause a decrease in heart rate, a condition known as bradycardia. As the body's metabolic processes become less efficient, individuals may experience a range of symptoms, including fatigue, depression, and cold intolerance, alongside the physical changes such as weight gain and bradycardia.

The other options do not align with the symptoms of weight gain and decreased heart rate. For instance, hyperthyroidism is characterized by an overactive thyroid, leading to weight loss and an increased heart rate. Osteoporosis primarily affects bone density and strength without direct involvement in weight or heart rate issues. Finally, cholesterol imbalance can influence cardiovascular health but does not directly cause the symptoms associated with decreased metabolic function.