Researchers have tracked thousands of people in the three decades since the mid-1980s to see what effect getting obese might have on their heart risks. They say this is one of the few studies that can give proof of the consequences of long-term obesity.

Follow-up of the 3,275 adults – who were not obese at the start of the research in 1985-1986 – found that those who became obese were more likely to have coronary artery calcification (hardening of the arteries supplying the heart), a problem that can lead to a heart attack.

Of the people who became obese, the earlier they did – and the longer they stayed overweight – the more likely they were to be at risk of coronary artery disease. This risk was decided by computed tomography (CT), a form of X-ray scan that was used to pick up artery calcification.

The research participants were aged between 18 and 30 years at the beginning of the study, which has just been published in the Journal of the American Medical Association. They were almost equal in numbers of men and women, and in proportion of white and black people.

Two measures of obesity were made at specific points during the long-term study. Overall obesity was worked out by measuring body-mass index (BMI), and abdominal obesity was measured by waist circumference. These checks were done at 2, 5, 7, 10, 15, 20, and 25 years after baseline.

Being obese was defined as:

  • Having overall obesity with a BMI of at least 30
  • Having abdominal obesity with a waist circumference of more than 40.2 inches (102cm) in men, 34.6 inches (88cm) in women.

During follow-up, 40% and 41% of the subjects developed overall and abdominal obesity, respectively. The average duration of each type of obesity was 13 years and 12 years, respectively. The CT scans to check for hardening of the coronary artery were done at 15 years (in 2000-2001), 20 years (2005-2006), and 25 years (2010-2011).

There was an almost double chance of finding hardened coronary arteries in the people who were obese for 20 years or more, compared with the people who had never become obese.

The researchers – Jared Reis of the National Heart, Lung, and Blood Institute, Bethesda, MD, and colleagues – give percentage values for these results: “Approximately 38.2% and 39.3% of participants with more than 20 years of overall and abdominal obesity, respectively, had coronary artery calcification, compared with 24.9% and 24.7% of those who never developed overall or abdominal obesity.”

Not only was the presence of artery hardening more likely in the obese people, but the longer people were too big, the greater the extent to which calcification got worse (disease “progression”).

The authors conclude:

“These findings suggest that the longer duration of exposure to excess adiposity as a result of the obesity epidemic, and an earlier age at onset, will have important implications on the future burden of coronary atherosclerosis and potentially on the rates of clinical cardiovascular disease in the United States.”

The study has been given the name CARDIA – Coronary Artery Risk Development in Young Adults. It is a large, multi-center, community-based study published in a world-renowned medical journal.

The design of the study, which set out to track future changes over time, means that the association between obesity and heart disease risk is a reliable one. This is because it was a “prospective” study as opposed to a “retrospective” one in which links are drawn from past data.