While the study wasn't designed to prove that a sedentary lifestyle causes heart disease or diabetes, the link between inactivity and risk factors for these illnesses remained strong regardless of age, gender, weight and whether participants got regular exercise.
"The take-home message is that reducing sedentary behavior is very important for maintaining favorable levels of blood lipids and sugars, and thus for the prevention of diabetes and cardiovascular disease, even in those who already meet physical activity recommendations," lead study author Qibin Qi, a researcher at Albert Einstein College of Medicine and Montefiore Health System in New York, said by email.
To explore the link between sedentary time and heart disease and diabetes, Qi and colleagues analyzed data collected from 2008 to 2011 among Hispanic residents of Chicago, Miami, San Diego and the Bronx in New York.
The researchers asked more than 12,000 people to wear activity monitors for 16 hours daily for one week; most participants followed through for at least one day. One average, they were inactive for about 12 hours daily.
Then, researchers sorted participants into four groups based on the amount of sedentary time they logged.
Compared to the group with the most physical activity, the least active group had 6 percent lower levels of high density lipoprotein (HDL) cholesterol, the good kind that helps reduce the risk for heart disease.
The least active group also had 16 percent higher levels of triglycerides, fats in the blood that can increase the risk of coronary artery disease. This group also had higher levels of sugar in the blood and less ability to process the hormone insulin, indicating a risk of diabetes.
Even when people met U.S. physical activity guidelines - at least 150 minutes a week of moderate intensity aerobic exercise or 75 minutes of vigorous workouts - more hours of sedentary time were still linked to an elevated risk of diabetes and heart disease.
Results were also similar regardless of participants' national origins.
One limitation of the study is that the motion trackers didn't distinguish between sitting and standing, the researchers acknowledge in Circulation, the journal of the American Heart Association.
Also, the study looked at risk factors, and not at "hard outcomes" like heart attack or stroke.
Even so, the results add to a growing body of evidence supporting the health benefits of not just an active lifestyle, but one that limits inactivity, said Peter Katzmarzyk, a researcher in obesity and diabetes at Pennington Biomedical Research Center at Louisiana State University.
"These results are entirely consistent with previous studies," Katzmarzyk, who wasn't involved in the study, said by email. "There is no reason to think that these associations would be any different in a Hispanic population versus other populations in the U.S."
Cardiovascular disease is the leading cause of death globally, with most fatalities linked to heart attacks and strokes, according to the World Health Organization (WHO). An unhealthy diet, obesity, inactivity, smoking and drinking can all increase the risk of developing these diseases.
Globally, about one in nine adults have diabetes, and the disease will be the seventh leading cause of death by 2030, according to the WHO. Most of these people have type 2 diabetes, which is associated with obesity and aging and happens when the body can't make or process enough of the hormone insulin to convert blood sugar into energy. Left untreated, diabetes can lead to nerve damage, amputations, blindness, heart disease and strokes.