Actress, writer, director, and producer Lena Dunham found that exercise was the key to getting on top of her emotional problems. "I know it's mad annoying when people tell you to exercise, and it took me about 16 medicated years to listen. I'm glad I did," she said.

We're also glad she found out how helpful exercise can be in reducing the symptoms of depression and anxiety. But researchers now say if she'd been active years ago she might actually have dodged the blues.

Research published in JAMA Psychiatry found that swapping out sedentary time for regular physical activity actually prevents depression.

The researchers say that you can get the protection with 15 minutes a day of high-intensity exercise such as running, cycling at 12-14 mph, singles tennis, soccer, or basketball; or with an hour of moderate-intensity exercise such as walking, playing doubles tennis, or cycling at 10-12 mph; or a combination of both. 

Exercise boosts endorphins and triggers release of a protein in the brain that prompts nerve cells to grow and make new connections, including in the hippocampus, the area of the brain that's associated with memory and mood. Better brain function means better mood regulation. 

The trick is to find exercise you enjoy so that you do it consistently. Try a bunch of things out if you're not certain what you like.

Some people thrive doing solo activities such as bike riding; others do well in a competitive setting like tennis or in a structured yoga or tae bo class.

Take a look: There's something out there for you.