[box]Cortisol is the primary stress hormone, when you undergo severe bouts of stress, your cortisol levels are much higher than normal. These increased cortisol levels can affect a myriad of bodily functions, including: immune system function, digestive system, reproductive system and even the natural growth process.[/box]
Cortisol and Immune Function
T-cells are a vital component of cell-mediated immunity, cortisol prevents T-cells from proliferating. Cortisol can also inhibit inflammation by limiting the histamine response. While chronic inflammation is a huge detriment to our health, inflammation in regulated amounts is actually a boon to our immune function and healing response. [1,2]
People suffering from chronic stress are extremely vulnerable to infection due to a limited immune response. The cells responsible for regulating our immune function are inundated with cortisol which essentially signals them to stop doing their job. The link between cortisol levels and immune function provides insight into just how detrimental stress can be to our health and well-being.
Regulating Blood Glucose Levels
Cortisol counters insulin by promoting higher blood sugar levels and stimulating gluconeogenesis. Cortisol also stimulated glycogen synthesis, which decreases blood sugar levels. Therefore it is quite effective at regulating blood glucose. This ability to regulate blood glucose comes in handy during periods of fasting. Helping to provide a constant supply of glucose via gluconeogenesis. 
Cortisol and Memory Loss
The hippocampus is the area of the brain where memories are stored as well as processed. It contains a plethora of cortisol receptors. Normal cortisol levels are tolerated well, with no adverse effects on the hippocampus. High cortisol levels however overwhelm the hippocampus and can cause atrophy. 
Individuals with chronically higher stress (cortisol) levels generally display severe memory loss, due to the damage caused to the hippocampus.
Naturally Lower Cortisol Levels
As a primary stress hormone, cortisol levels can be lowered naturally by reducing stress levels. Here are a few tips to naturally reduce cortisol levels:
People who regularly practice Buddhist meditation show a significant decreased level of cortisol as well as blood pressure levels. 
Music has a remarkable effect on our brain, calming our thoughts and reducing stress levels. It is especially beneficial when in a stressful situation. Try putting on some soothing background music during the most stressful areas of your day. 
When we don’t get enough sleep, our body suffers. When individuals got 6 hours of sleep, their cortisol levels were 50% higher than those who got the recommended 8 hours. If you get a poor sleep and fall short of 8 hours, take a nap, this can help lower cortisol levels in individuals who got a poor sleep the night before. 
Tea drinkers already know about the calming effect it has, and the science confirms it. Individuals who regularly enjoy a cup of black tea were found to have significantly lower cortisol levels than non-tea drinkers following an acute stressful episode.
It is difficult to be stressed out when you are laughing and having fun. Therefore it is no surprise that it can cut cortisol levels almost in half.