A new study found that metabolic abnormalities in non-Hispanic black women place them at greater risk of heart disease than non-Hispanic white women. The study was published in the Journal of the American Heart Association on May 20, 2015 and publicized by NPR on May 21, 2015.
Race and Metabolism Heart Health Q&A
Q: What population did the researchers study, and why were they chosen?
The Women’s Health Initiative (WHI) is a research study that has followed a large group of postmenopausal women (ages 50 to 79 at baseline) in the United States for many years, with recruitment starting in 1993-98 and with an additional group added in 2005-10. The current study looked at a multiethnic group of 14,364 of these women (47 percent white, 36 percent black, 18 percent Hispanic) who did not have heart disease, stroke, or diabetes when they entered the study. The researchers chose this group to see how different metabolic risk factors and obesity observed at the time of enrollment would affect the risk of developing heart attack or stroke and to see if the effects differed according to race and ethnicity. Previous research in this area had looked primarily at white women, so the researchers wanted to include a significant number of black and Hispanic women in the current study.
Q: What is metabolic syndrome? What causes it? What does it mean to be “metabolically healthy obese”?
Metabolic syndrome is a group of related abnormalities in how the body uses and stores energy. These factors, alone and in combination, raise the risk for cardiovascular disease and diabetes. A common definition of metabolic syndrome, and the one used in this study, is three or more of the following: increased abdominal fat (waist circumference), increased triglyceride level, decreased level of “good cholesterol” (HDL-C), elevated blood pressure, and elevated fasting glucose level. Metabolic syndrome is caused by a number of factors including genetic predisposition, poor nutrition, obesity, lack of exercise, stress and inflammation, increasing age, and environmental exposures.While obesity is often associated with metabolic syndrome, there is a subset of obese people who do not meet the criteria. These people are referred to as “metabolically healthy obese,” though there is controversy about whether this term should be used. In general, people who are obese have higher risk for cardiovascular disease and diabetes, but there has been interest to determine if this is a direct effect of obesity, or if it is because obesity is often, but not always, associated with metabolic syndrome.
Q: How was the study conducted?
The researchers followed the participants for an average of 13 years using annual mailed questionnaires to determine the time to a first heart attack or stroke. They categorized the population according to their metabolic health status (whether they met criteria for metabolic syndrome or not, and by number of metabolic risk factors) and by body mass index (BMI; normal weight, overweight, or obese).They then used statistical methods to determine the relationship between metabolic risk, obesity, and the frequency of heart attack or stroke. They looked at each race or ethnicity group separately to determine if the effects were different. (Because of a lower number of Hispanic women in the study, the results were most conclusive for white and black women). They adjusted for age, smoking, hormone use, and other risk factors at baseline in their main analyses.
Q: What did the researchers conclude?
As BMI increased, all components of the metabolic syndrome became more common, as did clustering of metabolic abnormalities. Over a median follow-up of 13 years, 7.7 percent of women had a first cardiovascular event. As expected, women with metabolic syndrome had increased cardiovascular risk regardless of BMI category in all racial and ethnic groups.Interestingly, white women who were “metabolically healthy obese” did not appear to have increased cardiovascular risk compared to normal weight metabolically healthy women, but “metabolically healthy obese” black women, in contrast, had a significantly increased cardiovascular risk compared with normal weight metabolically healthy women. Among women with metabolic syndrome, normal weight black women had higher cardiovascular risk than normal weight white women, overweight black women had a trend toward higher cardiovascular risk than overweight white women, and obese black women had higher cardiovascular risk than obese white women.The researchers concluded that among postmenopausal women without diabetes or prior cardiovascular disease, the risk of developing cardiovascular disease was more strongly associated with the presence of metabolic abnormalities than with the presence of obesity, regardless of racial or ethnic background. However, they concluded that obesity itself seemed to confer additional risk in black women but not in white women and that the use of the “metabolic syndrome” to define the metabolically healthy obese group appears to underestimate risk among black women and to overestimate cardiovascular risk in white women.
Q: What does this mean for treating metabolically healthy obese black women? Or people in general?
The results of this study suggest that a simple definition of metabolic syndrome may not accurately identify a woman’s cardiovascular risk. Instead, an individualized approach that considers the sum and the type of metabolic syndrome components in light of a patient’s overall risk profile should be encouraged, especially for non-white patients.The findings also suggest that the concept of “metabolically healthy obese” should be used with caution, and particularly may not be appropriate for black women. The researchers conclude that even “in the absence of metabolic syndrome, obesity might still be associated with increased metabolic risk among black women and thus the need for lifestyle intervention as a ‘window of opportunity.’ Our findings underscore the importance of preventing the development of metabolic disorders, particularly in black overweight and obese women, in whom metabolic disorders were more strongly associated with increased cardiovascular risk than in white women.”
Q: How does obesity increase the risk of heart disease?
Obesity, especially long-standing obesity, is associated with long-term cardiovascular risk, but research has suggested that most of this risk is because obesity is associated with insulin resistance and the development of other metabolic abnormalities. The current study, however, suggests that in post-menopausal black women at least, there may be either direct cardiovascular risks from obesity, high rates of transition from “metabolically healthy obese” to metabolic syndrome over time, or that obesity may be related to other risk factors that aren’t included in the current definition of metabolic syndrome.
Q: Physical inactivity, smoking and high blood pressure are also contributing factors to the heart disease risk in black women. As compared to women of other races, black women are also more likely to die at an early age. Do we have any insight into why black and white women possess different levels of cardiovascular risk? How do these factors affect heart health?
African-American women are at higher risk for heart disease and stroke. According to the American Heart Association, 49 percent of black women age 20 and older have heart disease, and black women have double the risk of stroke compared to white women. There are a number of suspected reasons for these facts, including genetics, environmental exposures, and health access. Scientists have identified genes that may make black people much more sensitive to the effects of salt, leading to high rates of high blood pressure. Higher rates of obesity and diabetes are found in some populations of black people, likely due to a combination of socioeconomic and cultural factors, that can though not always include lower access to high quality nutrition and health care, higher rates of inactivity, and probable genetic predispositions.
Q: What type of follow-up study would you suggest to advance or expand these findings to other populations and contribute to more individualized health care?
Further research would be useful to build on the results of this study. It would be important to see if the findings are consistent in other populations, and if they could be extended beyond post-menopausal women to men, younger women, or other racial or ethnic groups. This study was only able to look at the presence or absence of obesity and metabolic abnormalities at baseline, but further research to evaluate how the duration of obesity affects the development of cardiovascular risk could be important to understand how obesity and metabolic syndrome are related. This type of observational study is important for understanding health and the development of disease, but the ideal next step would be toward randomized trials of interventions aimed at identifying and treating women at risk for cardiovascular disease to protect women from heart attack and stroke.
Heart Health Q & A is a collaboration of Women’s Health Research at Yale and the OhioHealth Healthcare System, a nationally recognized not-for-profit organization with providers across 46 counties, offering a holistic approach to prevention, treatment and rehabilitation of heart disease. OhioHealth is staffed by physicians, psychologists, nutritionists and nurses who answer the questions of the moment on heart and vascular health. The information provided here may help you make more informed choices. However, it is not a substitute for an individualized medical opinion or diagnosis, and everyone should always consult with their personal physicians to make decisions about their condition or treatment.
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