"The way to develop the best in a person is by appreciation and encoragement."

Grateful? Write it down. Think about it. Talk about it. 'Tis the season of thanking, and not only will you spread those positive vibrations to those around you, your health will benefit, too.

For those who tend to be more Grinch-ish than grateful, there's some hard evidence that might make you want to turn that frown upside down. A positive outlook and feelings of thankfulness can have a direct and beneficial effect on the brain and body.

"If [thankfulness] were a drug, it would be the world's best-selling product with a health maintenance indication for every major organ system," said Dr. P. Murali Doraiswamy, head of the division of biologic psychology at Duke University Medical Center.

While the act of being thankful is not a substitute for a proper medical diagnosis and treatment, Doraiswamy said it's certainly a strategy that can be used to enhance wellness.

Studies have shown measurable effects on multiple body and brain systems, said Doraiswamy. Those include mood neurotransmitters (serotonin, norepinephrine), reproductive hormones (testosterone), social bonding hormones (oxytocin), cognitive and pleasure related neurotransmitters (dopamine), inflammatory and immune systems (cytokines), stress hormones (cortisol), cardiac and EEG rhythms, blood pressure, and blood sugar.

"When my coaching clients ask me why gratitude exercises work, I let them know that humans have something called a negativity bias where 'bad stuff' in our life outweighs the good by a measure of about 3:1," Renee Jain, a certified coach of positive psychology, wrote in an email.

"This bias developed over millions of years help us survive threats in our environment," said Jain. "Fortunately, we no longer have to worry about a saber-toothed tiger attacking us on the way to work. Unfortunately, we still have this bias, which makes us hone in on negative events, emotions, and interactions in our lives."

The brain's fundamental organizing principle in life is to avoid threat and maximize rewards, said Mitch Wasden, CEO of Ochsner Medical Center in Baton Rouge, who holds a doctorate in human and organizational learning. Because of this, the "chemical cocktail surging through the body allows humans to feel rewards and threats," he said.

"The brain's primary reward chemical is called dopamine," continued Wasden. "The interesting thing, however, is that we can't feel rewards and threats unless we focus attention on them. Many good and bad things happen in our life every day, but until they come to our own attention, we don't get the neurotransmitter release that allows us to feel good or bad."

But there's a twist. The brain doesn't know the difference when it's reacting to reality, fiction or even past events, which explains why people feel scared while watching horror movies even though they know it's not real or they cry when reading a sad novel. Feeling thankful for things that have happened acts as a "mental movie," Wasden explained. The brain releases dopamine, which, in turn, has a positive effect on mood and emotional well-being.

"I find positive psychology strategies can be particularly helpful for some people with mild depression and for those with poor psychosocial coping styles," said Doraiswamy. "Clearly if someone has severe depression or is suicidal they need urgent medical management for acute care but even there positive psychology strategies may reduce their risk for relapse or increase compliance with their treatments."

"Gratitude helps us counteract the negativity bias by focusing our attention on the 'good stuff,'" Jain said. "A little focus can go a long way to improving one's psychological, social, and physical health."

If it's tough to get out of a negative-thinking rut, Wasden suggested keeping a journal of things, big or small, for which you are grateful. Write letters of gratitude and meditate on positive emotions.

"One of the most well-known practices uncovered from this research is known as the Three Blessings exercise," said Jain. "Each night before going to bed you write down three good things (ordinary or extraordinary) that happened to you during the day. Studies reveal those who continue this exercise for one week straight can increase their happiness and decrease depressive symptoms for up to a six-month period."

Thank you for reading. Now, go express gratefulness to that special person, place or thing in your life. Write it down or yodel it from the rooftops. Hey, it's for the good of your health.