Exposure to high levels of noise increases blood pressure

Newswise — A new study by University of Michigan researchers suggests working in loud places can raise blood pressure levels.

Sally Lusk, professor emerita of the University of Michigan School of Nursing who has studied noise's effects on hearing loss for years, said her latest project gives one more reason for concern.

"The literature suggests bringing down your blood pressure will help prevent heart disease and stroke," Lusk said, "so understanding the relationship between noise and blood pressure is important."

The findings, which are published in the latest issue of Archives of Environmental Health, were based on a study in a Midwest auto assembly plant that connects noise exposure with elevated levels of systolic and diastolic blood pressure and heart rate. Blood pressure readings are given as two numbers, with one above or before the other, such as 120/80 mm Hg. The top number is systolic and the bottom is diastolic.

Because people spend so much of their waking time at work, blood pressure levels on the job are an important part of health, even if those levels decline after outside of work, she said.

Lusk and her collaborators studied different types of noise in the factory setting: continuous "usual" noise (recorded between 41-103 decibels), elevated continuous noise (found to be between 46-124 decibels), and spikes in instantaneous loud noises (113-145 decibels).

While others have looked at blood pressure in factory settings before, the team took a new approach---outfitting participants with mobile monitors to take blood pressure readings and record noise levels throughout the day. Noise readings were taken every minute, while heart rate and blood pressure were taken every 10 minutes.

The researchers conclude that blood pressure is more affected by overall noise exposure while the instantaneous peak noises affect heart rate. Noise exposure is both acute and chronic, as it seems to play out physiologically in multiple ways.

An increase in 10 decibels in average noise exposure resulted in a systolic blood pressure increase of two millimeters of mercury, the units in which blood pressure is measured. The same effect came when the difference between maximum and average noise increased by five decibels.

An increase of 13 decibels in average noise exposure led to a two millimeter increase in diastolic blood pressure. Everyday conversation is about 60 decibels, compared to about 80 decibels for heavy city traffic or running a vacuum cleaner, for comparison, according to the U.S. Occupational Safety & Health Administration.

Lusk noted that a long-term reduction of six millimeters in diastolic blood pressure has been associated with a 35-40 percent reduction in strokes and 20-25 percent reduction in coronary disease.

Using hearing protection to reduce noise levels entering the eardrum was significantly associated with keeping systolic blood pressure lower, and while the effect on diastolic pressure was statistically significant, the effect was in the same direction, Lusk said.

In hearing protection, previous research demonstrates the importance of wearing earplugs or earmuffs 100 percent of the time---even 30 minutes without protection cuts their effectiveness in half, Lusk said.

Helping workers reduce health problems associated with noise requires a multifaceted approach, Lusk said. In the best-case scenario, management would enforce use of hearing protection, appropriate training would be provided to employees, and reminders like posters in lunchrooms would explain to employees why hearing protection matters.

Lusk's coauthors were Brenda Gillespie, a biostatistics faculty member and associate director of the U-M Center for Statistical Consultation and Research, and Bonnie Hagerty and Rosemary Ziemba at the U-M School of Nursing.

This research was funded by the United Auto Workers-General Motors Corp. National Joint Committee on Health and Safety.