Using data from the European Social Survey, which interviewed about 50,000 people in European countries, Mutz found that people remain positive throughout most of the year, but they tend to have more negative thoughts during the holiday season. This is for a number of reasons, like social obligations, financial stresses or time management concerns.
As Mutz explains in the paper, the Christmas season often calls for believers to become more involved in their church and its events, which will often reinforce religious beliefs for Christmas celebrators, leading them to a higher level of life satisfaction and well-being.
"As a religious celebration, Christmas is closely interconnected with these values," Mutz wrote. "Attending religious services, intensifying prayer, watching nativity plays, donating for poor and needy persons, spending time and exchanging gifts with family and friends may be regarded as ways in which basic Christian values manifest themselves and are reinforced."
The study isn't foolproof, though. As Mutz pointed out, the researchers only interviewed a few participants around Christmas day, whereas most were interviewed a week before Christmas Eve — a time when people's stress levels often increase.
It's also important to note that just symbols and signs of Christmas and the holiday season often reduce the mood and well-being of non-Christians, since people of other religions, like Sikh and Buddhists, feel like they're not included in that environment.
In general, though, religion has been known to make people happier. A 2014 study from the Austin Institute for the Study of Family and Culture found that there's a link between religiousness and life satisfaction. Specifically, the study found that 45 percent of people who go to a religious service on a weekly basis are "very happy," whereas 28 percent of those who never attend church report the same.
"Being surrounded by friends and a congregation who share common beliefs and motivations is reportedly a key way in which faith and happiness connect," according to the Daily Mail.
Still, researchers are unsure if religion makes people happier. Scott Schieman, a professor at the University of Toronto, told US News that researchers often don't report on whether it's the religion that makes people happier, or if it's the specific event or church activity that inspires happiness.
"Is it the activity? If so, which kind of activity? Is it the belief? If so, is it (a belief in) life after death?" Schieman asked.
Similarly, Idler suggested that religions often perpetuate certain lifestyle choices that lead to longer lives and healthier well-being, like "injunctions against smoking," she said.
But Janet Ramsey, a pastor and theology professor at Luther Seminary in Minnesota, said religion supports people in other ways, like giving them meaning in their lives. And it helps them feel "a sense of closure," which allows them to forgive people and lead them to a happier life.
"Some language and beliefs and rituals are provided (by religion) that help people with their needs for forgiveness," Ramsey told US News. "We finally make peace with the things we have done."