Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health. It is performed for many different reasons. These include strengthening muscles and the cardiovascular system, honing athletic skills, weight loss or maintenance and for enjoyment. Frequent and regular physical exercise boosts the immune system, and helps prevent the "diseases of affluence" such as heart disease, cardiovascular disease, Type 2 diabetes and obesity. It also improves mental health and helps prevent depression. Childhood obesity is a growing global concern and physical exercise may help decrease the effects of childhood obesity in developed countries.