For many of us Thanksgiving - and the other festivals throughout the year - offer a good excuse to catch up with family and friends, and indulge in our favourite foods.
But actually 'giving thanks' - expressing gratitude to another person, whether verbally, physically, or even in the form of a letter - has profound effects on us, not just mentally but physicallly.
Ungrateful people are actually cheating themselves, scientists believe.
The mere act of thanking people releases chemicals within the body including 'reward' chemicals such as dopamine and serotonin - a neurotransmitter that makes us feel serene and happy - and oxytocin, the 'cuddle' hormone that loving couples release when together.
'If thankfulness were a drug,' says Dr. P Murali Doraiswamy, of Duke University, ' It would be the world's best selling product.'
'It affects every major organ system.'
Stress hormones such as cortisol are also reduced by the simple act of thanking someone.
Another study at Kent State University, Salem, measured the effect.
Steve Toepfer had a sample group of students write letters of gratitude to people they knew - thanking them for something that was important to them.
Toepfer ensured the 'thanks' weren't for trivial events such as a gift, but for genuine, meaningful events.
One group of students didn't write letters, one did.
The group that wrote the letters found that their levels of life satisfaction increased - and that those who were experiencing mild depression found that their symptoms abated.
The key, it seems, is genuine gratitude: your body has to 'know' that a positive event has occurred, and that you've responded.
Our bodies' 'reward' systems are conditioned to ignore a lot of events - to dismiss them as 'noise'.
'If you're looking to increase your well-being, take 15 minutes to write letters of gratitude to someone,' said Toepfer, who published his study in the Journal of Happiness Study.
By thanking someone, you draw your conscious mind's attention to the fact that something good has happened - provoking a neurotransmitter release.
The effect is so measurable, it can even be used to help people with mild depression, says Doraiswamy. Simply being polite can 'trigger' the brain to release 'reward' chemicals and make people feel happier.
'I find the strategy can be particularly helfpul for some people with mild depression and for those with poor psychosocial coping skills,' he says.
Toepfer advises that gratitude isn't just a strategy - it's a resource that we shouldn't ignore.
'We are all walking around with an amazing resource, gratitude,' Toepfer told Livescience. 'We all have it, and we need to use it to improve our quality of life.'
© Daily Mail, London