Fat Content Inside the Abdomen Helps Predict Whether Japanese Americans Develop Hypertension

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The summary below is from the full report titled "Visceral Adiposity Is an Independent Predictor of Incident Hypertension in Japanese Americans." It is in the 15 June 2004 issue of Annals of Internal Medicine (volume 140, pages 992-1000). The authors are T. Hayashi, E.J. Boyko, D.L. Leonetti, M.J. McNeely, L. Newell-Morris, S.E. Kahn, and W.Y. Fujimoto.

What is the problem and what is known about it so far?

Previous studies suggest that people with expanded waists (central or abdominal obesity) have increased risks for high blood pressure. Some of these studies looked at people at a single point in time. Such studies cannot show how often obese patients become hypertensive later in life and whether the obesity precedes hypertension. The results of prospective studies, which follow people with and without expanded waists over a period of years, are mixed. Some experts think that people with large amounts of fat inside their abdomen (around the internal organs or viscera) rather than just under the skin are at increased risk for high blood pressure. Computed tomography (CT) scans detect fat both inside the abdomen and under the skin. No prospective studies use CT scans to measure fat, and, therefore, we cannot determine whether the fat inside the abdomen is really the fat that increases the risk for hypertension.

Why did the researchers do this particular study?

To learn whether a large amount of fat inside the abdomen predicts hypertension in persons who are followed up over several years.

Who was studied?

300 second- or third-generation Japanese Americans, age 34 to 74 years, with normal blood pressure.

How was the study done?

Participants with normal blood pressure were selected from a group of people who had volunteered to take part in a study called the Japanese American Community Diabetes Study between 1983 and 1988. All had blood tests to measure glucose and insulin levels, and all answered questions about exercise, smoking, and alcohol-drinking habits. Weight and waist circumference were measured, and CT scans measured the amount of fat beneath the skin and in the abdomen. Participants were then followed for up to 11 years to see who developed hypertension.

What did the researchers find?

Almost 1 in 3 persons (92 of 300) developed hypertension. Compared with those having the least fat inside the abdomen, those with the largest amounts were more than 4 times more likely to be hypertensive at follow-up. This finding held up after adjustments for many other factors, such as age, sex, body weight, exercise, and smoking habits and glucose and insulin levels. Analyses that looked at many measures of fat showed that no other measures—even total fat and waist size—predicted hypertension.

What were the limitations of the study?

Only Japanese Americans took part in the study. The findings might not apply to other ethnic groups. The study does not explain why a large amount of visceral fat increases the risk for hypertension. Amounts of fat were measured only at the start of the study and could have changed over time.

What are the implications of the study?

Japanese Americans who have large amounts of visceral fat more often develop hypertension than do those who have small or normal amounts of visceral fat.