You can ward off seasonal depression by counting your blessings, says a UC Davis psychologist.

"Because gratitude is focused on the present and the past, it aligns your expectations closer to reality," says psychology professor Robert Emmons, whose co-edited book "The Psychology of Gratitude" will be published in January.

People often have unhappy holidays because they have unrealistic expectations for perfection among their loved ones, Emmons says. Christmas is also a time when people reflect on the gap between their current situation and where in life they wish they were.

"Gratitude, by contrast, is a deepened appreciation of circumstances in your life right now vs. where you want to be," Emmons says. "Feeling gratitude reduces unpleasant feelings like envy, resentment and regret that rob people of happiness."

In a series of experiments, Emmons found that when people consciously practice grateful living, they are happier, and their ability to withstand negative events improves as does their immunity to anger, envy, resentment and depression. Rather than objective life circumstances, individual happiness is a function of outlook and perception, the psychologist says.

Emmons' gratitude research participants experienced fewer symptoms of physical illness than those in the other groups, spent significantly more time exercising and were more likely to report having offered emotional support to others.

In another study focusing on people with either congenital or adult-onset neuromuscular diseases, Emmons found that their gratefulness practices not only fostered daily positive feelings but also reduced daily negative emotions and increased overall life satisfaction.