Hypertension Watch

Published Online: Monday, May 16, 2011

Study Identifies Possible Cause of Salt-Induced Hypertension

A new study sheds light on an issue that has baffled researchers for decades: the mechanism behind salt-induced hypertension.

The inability to explain why salt raises blood pressure in some individuals but not others has hindered understanding of what causes most cases of hypertension. In a study published in the April issue of Hypertension Research, a team of researchers led by Robert P. Blankfield, MD, MS, of Case Western Reserve University School of Medicine, and Ellen L. Glickman, PhD, of Kent State University, set out to test whether the dual roles of the cardiovascular system in maintaining normal blood pressure and helping to regulate body temperature might help explain how salt ingestion leads to salt-sensitive hypertension.

The authors examined the effect of salt and water consumption versus water alone in a group of 22 healthy men without hypertension. Subjects’ blood pressure, rectal temperature, cardiac index, and urine output were monitored at 1, 2, and 3 hours after they ingested either salt and water or water alone, and changes in rectal temperature were compared between those who were identified as salt sensitive versus those who were salt resistant.

They found that the ingestion of salt and water lowered body temperature more than the ingestion of water alone. In addition, body temperature decreased more in individuals who are salt resistant than in those who are salt sensitive.

“It appears that salt sensitive individuals maintain core body temperature equilibrium more effectively than salt resistant individuals, but experience increased blood pressure in the process,” Dr. Blankfield said. “Conversely, salt resistant individuals maintain blood pressure equilibrium more effectively than salt sensitive individuals following salt and water intake, but experience a greater temperature reduction in the process.”

Shielding Boys from Secondhand Smoke May Lower Risk of Hypertension 

Exposure to secondhand smoke, even at extremely low levels, is associated with elevated blood pressure in boys, which increases the risk of developing hypertension in adulthood, according to research presented at the Pediatric Academic Societies’ annual meeting in May.

Previous studies of nonsmoking adults have uncovered links between both secondhand smoke and outdoor air pollution with increased blood pressure, but until recently, no research had examined the relationship in children.

A team of investigators led by Jill Baumgartner, PhD, of the University of Minnesota, assessed exposure to secondhand smoke among 6421 youths as determined through their own reports of whether they lived with a smoker, and through levels of cotinine, a substance produced when the body breaks down nicotine. Analysis demonstrated that boys aged 8 to 17 years who were exposed to secondhand smoke had significantly higher systolic blood pressure than those who were not exposed.

“While the increases in blood pressure observed among boys in our study may not be clinically meaningful for an individual child, they have large implications for populations,” said Dr. Baumgartner.

The research also showed that girls who were exposed to secondhand smoke had lower blood pressure levels than girls who were not exposed to tobacco smoke.

“These findings support several previous studies suggesting that something about female gender may provide protection from harmful vascular changes due to secondhand smoke exposure. An important next step is to understand why,” Dr. Baumgartner added.

For Kids, Watching Too Much TV Now Can Lead to High BP Later

The argument to limit the number of hours children spend watching TV just got stronger.

According to a study published in the May issue of Arteriosclerosis, Thrombosis and Vascular Biology, children who logged the most screen time had narrower arteries, which is a possible indicator for cardiovascular disease, including hypertension. Researchers determined that more sedentary behavior—which included watching television, using a computer, or playing video games—was associated with an average narrowing of 2.3 microns in the retinal arteriolar caliber.

In the study, children aged 6 to 7 years who regularly participated in outdoor physical activity had 2.2 microns wider average retinal arteriolar compared with those children with the lowest level of activity. The magnitude of the narrowing associated with each hour of screen time was similar to that associated with a 10 mm Hg increase in systolic blood pressure in children, according to lead author Bamini Gopinath, PhD, senior research fellow at the Center for Vision Research at the University of Sydney.

“We found that children with a high level of physical activity had a more beneficial microvascular profile compared to those with the lowest levels of physical activity,” said Dr.Gopinath. “This suggests that unhealthy lifestyle factors may influence microcirculation early in life and increase the risk of cardiovascular disease and hypertension later in life.” PT



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