Western medicine has significantly downplayed the role of your mental state on your physical health.  It's been foo-fooed with comments of "it's  all in your head" or a likeness of that statement.

In Bruce Lipton's book "The Biology of Belief," he explains the effect of thought on the body from his research on stem cells.  In his research, he took a single stem cell and let it replicate again and again until there were a couple thousand stem cells in a petri dish.  All the genetic material is therefore the same because all the cells are copies of the original.  He then took 3 additional petri dishes in which he supplied different culture mediums, or environments, for which he could place a clump of stem cells from the original petri dish.  Amazingly, in one dish, the stem cells became muscle, in another, they became bone and in the third, they became fat tissue.  So it wasn't the genes that made the determination of what tissue was formed, but rather the environment.

What controls the environment in which the cells are being bathed? It's the interstitial fluid, which is derived from your blood.  And what controls what's being released into your blood stream, but your neuro-endocrine system.  You activate different parts of this system based on what you're thinking about.  If you're under a lot of stress, then your sympathetic or "fight or flight" component of your nervous system kicks in and if you are relaxed, then your parasympathetic or healing component of your nervous system kicks in.  Depending on which component is being activated will determine which group of hormones and neuropeptides are being secreted into your blood and therefore what kind of environment your cells are being bathed in.  So, quite literally, your thoughts are controlling which genes are being suppressed and which ones are being expressed.

The thoughts and feelings of gratitude activate your parasympathetic and healing response in your body.  Take the time each day to make it part of your lifestyle and reap the benefits of a healthier you.