The findings highlight yoga's effectiveness "in the absence of a heated practice environment, in improving vascular health," the study authors wrote.
The findings were important, they added, "given the increased propensity toward heat intolerance in ageing adults."
The team enrolled 52 "sedentary but apparently healthy" adults aged 40-60 for the trial.
They were divided into three groups, two of which did yoga three times a week for 12 weeks, and a third "control" group which did none.
One of the yoga groups exercised in a room heated to 40.5 C, the other at 23 C.
"The heated practice environment did not seem to play a role in eliciting improvements in vascular health with bikram yoga," said study co-author Stacy Hunter of Texas State University.