Women nearing menopause have higher levels of a brain protein linked to depression than both younger and menopausal women, according to a study published in the U.S. journal JAMA Psychiatry Wednesday.

The findings may explain the high rates of first-time depression seen among women in this transitional stage of life known as perimenopause, said the study by researchers at Canada's Center for Addiction and Mental Health.

"This is the first time that a biological change in the brain has been identified in perimenopause which is also associated with clinical depression," senior author Jeffrey Meyer of the center said in a statement.

During perimenopause, a common symptom is mood changes such as crying. Rates of first-time clinical depression among this group reach 16 to 17 percent, and a similar number get milder depressive symptoms.

Meyer has previously linked high levels of a protein called monoamine oxidase-A (MAO-A) to major depressive disorder, depressed mood related to alcohol dependence and smoking cessation, and the period immediately after childbirth.

According to Meyer's research team, MAO-A is an enzyme that is a pro-oxidant and breaks down brain chemicals such as serotonin, norepinephrine and dopamine, which help to maintain normal mood.