Puerto Ricans have a higher death rate linked to high blood pressure than blacks, whites or other Hispanic-Americans do, federal health researchers said Thursday in one of the first analyses of specific U.S. Hispanic populations.

Health officials don't know why and said more study is needed to find the cause. One expert said it could be related to health care, diet or genetics.

Puerto Rican-Americans had 154 high blood pressure-related deaths per 100,000 people in 2002, according to the researchers' review of death certificate data.

For Mexican-Americans, the rate was 134.5 and for Cuban-Americans, 82.5 that year. Among non-Hispanics, the black rate was 138, and the white rate was 136.

It's not clear why the Puerto Rican death rate was so high, said Dr. Carma Ayala, the report's lead author and an epidemiologist with the federal Centers for Disease Control and Prevention. "We really need to do more studies to find that out," she said.

Of all racial groups, blacks have the highest rate of high blood pressure, and Hispanics and non-Hispanic whites have the condition at about the same rate.

The report was published in the CDC's Morbidity and Mortality Weekly Report.

Previous studies have focused on differences between blacks, whites and Hispanics, but this may be the first to look at the differences between Hispanic sub-populations, said Dr. Steven V. Manoukian, a cardiologist and official with the American Heart Association.

The data is important because it may lead to new clinical studies and public health education efforts, he said.

High blood pressure — also known as hypertension — is considered a major risk factor for heart disease and stroke, and an important predictor of premature death and disability. The condition can result from obesity and physical inactivity.

Manoukian said he was surprised to learn of the high rate reported for Puerto Ricans. He said there could be a range of possible explanations, include genetics, access to health care, and cultural differences that might influence diet or willingness to exercise or seek health care.

The CDC researchers looked for ethnicity in death certificates for people who were 25 and older when they died. Since 1995, information on Hispanic ethnicity has been provided on nearly all U.S. death certificates.

The records were from the 50 states and the District of Columbia and 1995-2002.

The researchers also looked for mention of high blood pressure associated with heart or renal disease as underlying or contributing causes of death.

Researchers found that hypertension-related death rates for Mexican-Americans rose 31 percent from 1995 to 2002, about 46 percent for most other Hispanic-Americans and 26 percent in non-Hispanic whites.

For Puerto Ricans, it actually decreased slightly. But the Puerto Rican death rate remained highest because it was so elevated to begin with, Ayala said.