The lower the better when you're talking about total cholesterol levels, right? Keeping total cholesterol levels below 200 mg/dL and your LDL (bad) cholesterol levels below 100 mg/dL are optimal and can reduce your risk for heart disease, but can you go too low? While it's well known that high cholesterol levels are linked to clogged arteries, heart disease and an increased risk for developing metabolic syndrome, some controversial studies show a correlation between low cholesterol levels and an increased risk for non-coronary deaths.

In 1994, the American Heart Association Task Force on Cholesterol Issues published a groundbreaking report about a link between total cholesterol levels of less than 160 mg/dL and an increase in deaths from trauma, some types of cancer, hemorrhagic stroke, and respiratory and infectious diseases. Since then, most additional research links very low cholesterol levels to an increased risk of depression, suicide, anxiety, impulsivity and aggression in men and women, adolescents and adults alike.

A study conducted in the late 1990s at the Duke University Medical Center found that otherwise healthy women with cholesterol levels below 160 mg/dL were more likely to show signs of depression and anxiety than women with normal or high cholesterol levels. Researchers in the Netherlands published a study in 2000 showing that middle-aged men with low cholesterol are more likely than other men to have symptoms of severe depression.

More recently, a study published in 2009 in the "Journal of Psychiatric Research" found that men with very low total cholesterol (165 mg/dL) and depression were at very high risk for premature death from unnatural causes: Men with low total cholesterol plus symptoms of depression were seven times more likely to die prematurely from suicides, drug overdoses, and accidents and injuries than those without those markers.

So what's the relationship between these two studies? Read on to find out.