New research suggests that it is not just being obese that increases the risk of heart disease, but also how long someone is obese for, with the number of years spent carrying excess weight "adding up" to a distinct risk factor for heart problems later in life.

A team from Johns Hopkins University looked at 9,062 participants with no history of cardiovascular disease and followed them between 1987 and 1998.

Participants were assessed four times during the study, with the team looking at body mass index (BMI), history of heart disease, and levels of troponin -- a protein released into the bloodstream during a heart attack and a sign of being at high risk of heart failure.

As well as having their weight measured during assessments, participants self-reported their weight at age 25 so researchers could track their BMI from young adulthood through late middle age and elderly years.

A BMI of more than 25 indicates that a person is overweight, and a BMI of more than 30 indicates obesity.

After looking at BMI from the beginning to the end of the study alongside participants' troponin levels, the team found that those whose BMI had increased to the overweight or obesity range by the fourth visit were 1.5 times more likely to have increased troponin levels of at least 14 nanograms per liter, indicating heart damage.

Participants who were obese at both the first and fourth visits were twice as likely as those with a consistently normal weight to have increased troponin levels to more than 14 nanograms per liter, and those who were obesity at both the fourth visit and at age 25 were almost four times more likely to have increased troponin levels.

After taking into account other heart disease risk factors such as high blood pressure, diabetes, and kidney disease, the researchers also found that for every 10 years that a person spent obese, their risk of having raised troponin levels increased 1.25 times, suggesting that it is not only being obese which is a risk factor for heart disease, but also the number of years spent overweight or obese.

The researchers say the findings underline that maintaining a healthy weight throughout life is important for keeping the heart healthy and minimizing the risk of problems.

Co-author Chiadi Ndumele added that although there is some evidence to suggest that losing weight even after decades of being obese or overweight may help reduce troponin levels, and to a certain extent help the heart to heal, how much the heart can be healed and how permanent the damage might be after years of obesity is still unknown and calls for further research.

The study was published in Clinical Chemistry.