Heart health in the US has generally improved since the start of the 21st century, but not for adults living in poverty, a new study suggests.

Between 1999 and 2014, high–income people had decreases in rates of high blood pressure, smoking and high risk for heart disease. The same wasn't true for low–income people, however.

An earlier study of risk factors for heart disease in the US in 1971–2002 also found more of them among low–income people–but "that was 10 years ago," lead author Dr. Ayodele Odutayo of the University of Oxford in the UK and St. Michael's Hospital in Toronto told Reuters Health. "So, it was quite dated and we didn’t have more modern information on this."

Odutayo and colleagues write in JAMA Cardiology that great strides have been made over the past two decades in reducing the number of people at risk for heart disease due to smoking, high blood pressure, high cholesterol and diabetes. It's unclear if everyone benefited equally from those improvements, though.

For the new study, the researchers used data collected from 17,199 participants, ages 40 to 79, in the US National Health and Nutrition Examination Survey.

Overall, there were no significant changes in risk factors for heart disease among people living below the federal poverty line.

For example, the proportion of low–income people with a 20% or greater risk of heart disease was about 15% between 1999 and 2004, and 16.5% between 2011 and 2014.

Also, the average systolic blood pressure among low–income people was about 128 mm/Hg during the earlier part of the study, and that only fell to about 127 mm/Hg at the end.

There was also no significant change in the proportion of low–income people who smoked over the study period.

High–income people did experience declines in all those measures, on the other hand. The proportion at high risk for heart disease decreased from 12% to 9.5% during the study period, for example. The average blood pressure dropped by nearly 4 mm/Hg, and the proportion of smokers fell by more than five percentage points.

Rates of diabetes and cholesterol did not vary by income.

Odutayo told Reuters Health that it will be important to look at data after 2014 to account for the increasing number of people gaining health insurance under the Affordable Care Act.

"It would be interesting to see if there are any changes," he said.

The data shows that primary care and prevention is important for people with low incomes, he added.

"It’s important that the insurance that people with lower income can obtain puts an emphasis on primary care medicine and preventive medicine," said Odutayo.

—Andrew M. Seaman