New European research has found that women who are obese but metabolically healthy still have a higher risk of developing cardiovascular disease than metabolically healthy women who are of a normal weight.

Carried out by the German Institute of Human Nutrition Potsdam-Rehbruecke, Germany, the large-scale study followed over 90,000 American women aged 30 to 55 for up to 30 years to assess how metabolic health changes over time and how body mass index (BMI) influences the risk of cardiovascular disease.

Obesity, which is defined as a BMI of more than 30, is already know to affect almost all of the risk factors for cardiovascular disease, including metabolic syndrome, a collection of conditions including high blood pressure, poor blood sugar control or diabetes, and abnormal blood fats, which double the risk of cardiovascular disease such as heart attacks and stroke.

However, some individuals have what is often referred to as "healthy obesity" and appear to be free of any metabolic abnormalities.

To investigate further the researchers divided the participants into groups based on their BMI category, their metabolic health (defined as the absence of three metabolic risk factors -- type 2 diabetes, high blood pressure, and high blood cholesterol), and change in metabolic health status.

All participants were asked to complete questionnaires every two years to update their BMI and metabolic health status, and to assess their lifestyle, health behavior, and medical history.

The researchers found that cardiovascular disease risk was especially high in all metabolically unhealthy women, regardless of whether they were normal weight, overweight, or obese.

More specifically, those who were metabolically unhealthy and a normal weight were around 2.5 times more likely to develop cardiovascular disease compared to women with metabolically healthy normal weight, while women with 'metabolically healthy obesity' had a 39 percent higher risk of cardiovascular disease than women with metabolically healthy normal weight.

Importantly, 84 percent of women who were initially metabolically healthy obese and 68% of normal weight metabolically healthy women, became metabolically unhealthy over a period of 20 years.

The findings indicate that obesity is a risk factor for cardiovascular disease, regardless of whether or not women develop any of the common metabolic diseases such as high blood pressure or type 2 diabetes.

"Our large cohort study confirms that metabolically healthy obesity is not a harmless condition, and even women who remain free of metabolic diseases for decades face an increased risk of cardiovascular events," explains lead researcher Professor Matthias Schulze.

"What's more, we observed that most healthy women are likely to develop type 2 diabetes, high blood pressure, or high cholesterol over time, irrespective of their BMI, putting them at much higher risk for cardiovascular disease."

Professor Schulze added that long-term maintenance of metabolic health which includes a healthy diet and physical activity could help protect all women against metabolic diseases.