DALLAS, Sept. 18--Researchers have identified a "salt gene" that helps explain the variation in an individual's response to a low-salt diet for reducing high blood pressure. The research is reported in this month's Hypertension: Journal of the American Heart Association.
The gene--called the angiotensinogen gene -- is thought to influence the effect of dietary salt on blood pressure. Increased blood levels of angiotensinogen, the hormone that the gene encodes, have been correlated with high blood pressure.
Researchers studied three forms or variations of the gene, referred to as AA, AG and GG. A person's sensitivity to salt -- meaning that they may fare better in lowering their blood pressure through salt restriction -- was associated with the type of gene variation.
"This is a first step in defining who is salt sensitive and who is not," says lead author Steven C. Hunt, Ph.D., professor of medicine at the University of Utah School of Medicine in Salt Lake City. "However, we are not to the point yet where we can say on an individual basis: If you have one particular form of the gene, the AA form, you are salt sensitive."
The researchers obtained blood samples from 1,894 people in a three-year study called the Trials of Hypertension Prevention (TOHP). Hunt's team studied a specific section of the angiotensinogen gene to determine which of three gene variations each person carried.
Because only 10 of 323 African Americans in the study carried the GG and only 62 participants represented other nonwhite races, the team could only do a meaningful analysis on the 1,509 Caucasians in the study.
TOHP participants were moderately overweight and had borderline high blood pressure. That is, their diastolic blood pressure -- the force pressing on blood vessels between heart contractions -- was between 83 and 89 millimeters of mercury (mm/Hg). This is below the level of 90 mm/Hg that doctors normally regard as high blood pressure.