Depression is one of the most common mental health disorders in the United States. It affects over 15 million adults annually, or 6-7 percent of the entire adult population. It is so common, in fact, that nearly everyone has either been affected by it personally or is involved in some way with someone who has/is.

Depression has serious costs to both individuals as well as employers. Major Depressive Disorder is the leading cause of disability in the U.S. in those aged 15 to 44, and depression is estimated to cost employers up to $44 billion annually. It ranks third in workplace issues, preceded only by family crisis and stress.

Now, neuroscience research has identified a stunningly effective yet simple way to significantly reduce depression symptoms: combining aerobic exercise with meditation.

The study comes out of work on neurogenesis, the study of how new neurons are created and develop in the brain.

In essence, neurogenesis researchers hypothesized that as depressive symptoms emerge, the production of new cells decreases. They noted that trauma and stressful life events are already known to impair neurogenesis, and that the literature has already established that aerobic exercise can significantly increase the number of new cells a brain creates.

The problem is what happens after aerobic exercise: a great number of new cells die just weeks after being created. And if they don't join the brain's circuitry, they can't bolster the brain, uplift mood, help a person experience resilience, or create a more robust sense of wellbeing.

Fortunately, while new neurons can die, they can also be rescued, which is where meditation comes in. It turns out that when novel learning experiences challenge the mind, new neurons are "saved."

"Mental training can rescue new neurons from death as long as the learning experience is new and effortful," the researchers state. "Collectively, these findings suggest that aerobic exercise increases the production of new neurons in the adult brain, while effortful mental training experiences keep a significant number of those cells alive."

The study, published in Translational Psychiatry, outlined how the research was conducted: The neuroscientists developed a mental and physical (MAP) training plan for participants, which combined focused attention meditation with aerobic exercise.

Both the control group and the group with major depressive disorder (MDD) started with 30 minutes of focused attention meditation, followed by 30 minutes of aerobic exercise. They completed this combination twice a week.

During the meditation portion, participants were instructed to focus on the present moment, refocusing on their breathing if thoughts drifted to the past or future. According to research, this helps those with depression (not to mention the rest of us) "accept moment-to-moment changes in attention." This was followed by 30 minutes of "moderate-intensity" aerobic exercise.

Remarkably, the study found a nearly 40 percent decrease in depressive symptoms after just eight weeks of the training. They described these results as "robust."

As Tracey Shors, one of the study authors said, "Scientists have known for a while that both of these activities alone can help with depression ... But this study suggests that when done together, there is a striking improvement in depressive symptoms along with increases in synchronized brain activity."

The researchers also pointed out that while the norm for treating depression has involved the prescription of psychotropic drugs like Zoloft, Prozac, Celexa, and Lexapro, these drugs can have limited efficacy and can also lead to intense and disruptive side effects. Part of the excitement over these results is the fact that the practices involved are free, immediately accessible, and have no adverse side effects.

Interestingly, in addition to student participants, the research group also provided MAP training to young mothers living at a residential treatment facility. The young women involved had experienced homelessness in the past, and had displayed severe depressive symptoms as well as elevated levels of anxiety.

After eight weeks of MAP, they too reported a significant reduction in symptoms of both depression and anxiety. They reported feeling much more motivated and able to focus positively on their lives -- at a time when such an attitude was imperative.

"We know these therapies can be practiced over a lifetime and that they will be effective in improving mental and cognitive health," said lead researcher Brandon Alderman. "The good news is that this intervention can be practiced by anyone at any time and at no cost."