A new, "ultra-bad" form of low-density lipoprotein (LDL) cholesterol has been discovered in people with a high risk for heart disease, according to British researchers.

They found that the cholesterol, called MGmin-LDL, is super-sticky, making it more likely to attach to the walls of arteries and form fatty plaques, which could lead to heart attacks and stroke.

The discovery provides a possible explanation for the increased risk of coronary heart disease in diabetics and could help researchers develop new anti-cholesterol treatments, the researchers suggested.

Antidepressants may not improve all symptoms of depression, according to a new study.

Researchers analyzed data from a U.S. National Institute of Mental Health-sponsored study of depression treatment, which involved more than 4,000 people with major depression around the country and is the largest study on depression treatment to date.

While antidepressant medications worked in general, all patients taking them reported three to 13 residual symptoms, and 75 percent reported five or more residual symptoms.

These symptoms included insomnia that occurs in the middle of the night (79 percent); sadness (nearly 71 percent), and problems with concentration and decision-making (nearly 70 percent), said the researchers at UT Southwestern Medical Center in Dallas.