One-quarter of girls and women between the ages of 16 to 19 will experience an episode of major depression and smokers are more likely to be depressed, according to a study at the University of Alberta.

The rate of depression for females is twice as high as for males, said Nancy Galambos, a psychology professor.

DEPRESSION Section: Mental Health Rankings: State-By-State Facts: Symptoms Of Depression FROM OUR PARTNERS Info: All About Depression Center: Mental Health Info Quiz: Are You Depressed

"Across the four-year period, the numbers for females (who had experienced depression) were typically twice as high as for males," said Galambos.

The study also found that decreases in social support and increases in smoking were both linked to increases in depressive symptoms.

"A link between smoking and depression has hardly ever been studied," said Galambos. "It might be that some people are smoking to self-medicate because they already feel bad. It's an interesting two-way relationship between smokers and depression that needs further investigation."

Depression in adolescence has been linked to problems with work, stressful life events, pregnancy, smoking and substance abuse. These adolescents are also at risk for anxiety, eating and conduct disorders, as well as academic failure and problems in interpersonal relationships.

The long-term study examined more than 1,300 teenagers between 12 and 19 years over a four-year period. The research team investigated the differences between male and female teens in risk factors for depressive symptoms and major depressive episodes (MDEs). The research was recently published in the International Journal of Behavioral Development.