Cortisol is known as the stress hormone. It is released in response to both physical and mental stress. However, too much stress and cortisol can be unhealthy. Cortisol is the only hormone in the body that usually increases with age. Excess cortisol can lead to thinning bones, a decreased immune system, increased fat deposition, and increased insulin resistance (a precursor to diabetes and heart disease). Less commonly seen are cortisol deficiencies. Too little cortisol can cause fatigue, low blood pressure, low blood sugar, and insomnia.