The question: Smoking cigarettes can do untold damage to your lungs and heart, but what exactly does the bad habit mean for your brain? A new study from Kings College London took a closer look at smoking's little-understood relationship with cognitive decline in an effort to answer that question.

How it was tested: British scientists working on the English Longitudinal Study of Ageing studied more than 8,000 adults — many of whom were smokers — over age 50. Participants had their mental abilities evaluated with basic tests like learning new words or naming as many animals as they could inside of a minute. These examinations were conducted three times: First at the beginning of the study, once after four years, and again after eight years. 

The outcome: The findings, published in the journal Age and Ageing, demonstrated a "consistent association" between smoking and lower test scores. At the end of eight years, high blood pressure and a high risk of stroke were also associated with lower scores for memory and overall mental ability. 

What the experts say: Previous studies have shown that roughly 30 percent of all deaths from heart disease in the United States are directly related to cigarette smoking, and this new research adds to an increasing body of evidence that smoking-related high blood pressure can gradually change the brain over long periods of time. "We have identified a number of risk factors which could be associated with accelerated cognitive decline, all of which could be modifiable," says lead scientist Dr. Alex Dregan. "We all know smoking, high blood pressure, high cholesterol levels, and a high BMI is bad for our heart," says Jessica Smith from the Alzheimer's Society. "This research adds to the huge amount of evidence that suggests they can be bad for our head too."   

The lesson: "One in three people over 65 will develop dementia," says Smith, "but there are things we can do to reduce their risk." Maintaining a healthy weight, exercising regularly, eating a balanced diet, and kicking the smoking habit sooner rather than later won't just do worlds of good for your heart and lungs — they can help keep your mind sharp, too.