According to the Anxiety and Depression Association of America, about 15 million Americans are currently suffering from depression. While doctors admit they haven't really discovered the concrete cause of this mental disorder, Yahoo Health reports there are other surprising factors that can trigger depression.

Various studies have pointed out health issues such as carb-heavy diet and thyroid problems, as well as how you keep up with the news and the amount of time spent on social media as triggers for depression.

In a research involving 70,000 postmenopausal women, experts have found a significant link between depression and diets high in refined carbohydrates. "Refined foods such as white bread, white rice, and soda trigger a hormonal response in the body to reduce blood sugar levels," the researchers concluded. "This response may also cause or exacerbate mood changes, fatigue, and other symptoms of depression."

Another possible factor that affects a person's mood is a malfunctioning thyroid that excretes hormones affecting all body organs including the brain. In fact, experts say that thyroid hormone medications are more effective than other depression pills.

Aside from what's going on inside your body, depression may also be triggered by the things happening around us. According to media studies, those who regularly watch or read news about bombings, killings and other disasters are more prone to feel sad and low than those who prefer watching happy stories.

But too much time looking at happy people on social media doesn't help either. According to a study published in the Journal of Social and Clinical Psychology, spending most of your time on Facebook can even worsen depressive symptoms.

To avoid falling into the pit of depression, experts advice to cut out refined carbs in your diet, read and watch positive news stories, and spend more time actually hanging out with friends than check on them in Facebook.