La Jolla, CA - African Americans have double the risk of peripheral arterial disease (PAD) compared with people from other ethnic backgrounds, a new study has found [1].

And the higher levels of diabetes and hypertension or higher BMIs found in blacks did not explain this, say Dr Michael Criqui (University of California, San Diego) and colleagues in their paper in the October 25, 2005 issue of Circulation.

"Doctors can now add another independent marker for PAD—African American ethnicity," Criqui told heartwire.

The researchers examined 2343 people ages 29 to 91 for the presence of PAD and compared rates among members of four ethnic groups—1401 non-Hispanic whites (NHWs), 322 African Americans, 341 Asians, and 279 Hispanics. Most were randomly chosen from current or retired employees of the University of California, San Diego and their spouses, and most participants had health insurance and access to medical care.

They used Doppler ultrasound to measure systolic blood pressure in the posterior tibial artery and calculated the ankle-brachial index (ABI). People were considered to have PAD if they had any of the following: an ABI of 0.90 or less; an abnormal Doppler waveform; or previous revascularization for PAD.

Previous studies of ethnicity and PAD have underestimated the occurrence of the disease by using only ABI criteria alone to diagnose PAD and by classifying people as unaffected if they currently showed good circulation but had previously undergone revascularization for PAD, Criqui et al point out.

Overall, there were 104 cases of PAD. Men (6.1%) were more likely to be affected than women (3.6%), and the rates of PAD increased sharply with age, roughly doubling for each decade, from 1.2% for those age 50 and younger to 10.2% for those age 70 or older.

In the ethnic-group comparisons, the researchers found PAD in 7.8% of African Americans, 4.9% of NHWs, 1.8% of Hispanics, and 1.4% of Asians.

"We did not have enough Hispanic or Asian participants to definitively exclude any ethnic differences in PAD, but there did not seem to be a pronounced difference," Criqui said. Also, he told heartwire, another study that has just been completed with greater numbers of Hispanics and Asians has not shown any strong signals that people from either of these backgrounds have any increased risk of PAD.

Several factors significantly raised the risk of PAD in the study—diabetes, hypertension, cigarette smoking, a ratio of high total cholesterol to low HDL cholesterol, and a history of cardiovascular disease. Even after adjusting for these factors, African Americans had 2.34 times the risk of NHWs.

The researchers hypothesized that the greater risk of PAD in blacks might represent less aggressive treatment of risk factors, but this did not appear to be the case. Drug treatment of dyslipidemia in African Americans was similar to that in NHWs, and antihypertensive therapy was, appropriately, more common in blacks.

"It had been presumed that the excess of PAD in African Americans was due to a greater proportion of African Americans having diabetes and hypertension," Criqui said. "Even though we found a link with those conditions, we were surprised that they explained only part of the risk. For reasons that are still unclear, something related to African American ethnicity raises the risk of PAD." Further work is needed to try to elucidate the cause, he says.

But in the meantime, "physicians need to be particularly alert to the possibility of PAD in their African American patients," Criqui stresses.  

"Their independent increased risk is as high as someone in another ethnic group 10 years older or someone their own age who smoked a pack of cigarettes [a day] for 20 years," he concludes.