Dec. 19 (UPI) -- Working late at the office may be hazardous to heart health.

A study published Thursday in the journal Hypertension has found that office workers who spent 49 or more hours per week on the job were 70 percent more likely than those who work 35 hours or less to have a form of high blood pressure called masked hypertension.


Masked hypertension is high blood pressure that is undetectable in regular blood pressure tests -- and it often goes undiagnosed.

"Both masked and sustained high blood pressure are linked to higher cardiovascular disease risk," lead author Xavier Trudel, assistant professor in the social and preventive medicine department at Laval University in Quebec, Canada, said in a press release.

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"The observed associations accounted for job strain, a work stressor defined as a combination of high work demands and low decision-making authority. However, other related stressors might have an impact," Trudel said

In general, high blood pressure affects nearly half of American adults and is linked with more than 82,000 deaths annually. Masked hypertension affects as many as 30 percent of U.S. adults.

For their new study, Trudel and his colleagues enrolled more than 3,500 white-collar employees from three public institutions in Quebec, and monitored them over a five-year period, with testing in years one, three and five. The authors simulated in-clinic blood pressure readings by providing participants with a wearable blood pressure monitor.

The device took three readings each morning, and every 15 minutes throughout the day, collecting a minimum of 20 measures daily. Average resting readings of 140/90 mmHg or higher and average working readings 135/85 or higher were considered high.

In addition to the increased risk for masked hypertension, those who worked 49 or more hours per week had 66 percent higher risk for having sustained hypertension, or elevated blood pressure readings in and out of a clinical setting. Those who worked between 41 and 48 hours per week had 54 percent higher risk for having masked hypertension and 42 percent higher risk for having sustained hypertension.

In all, nearly 19 percent of the workers had sustained hypertension, including participants who were already being treated for high blood pressure. More than 13 percent of the workers had masked hypertension. The authors accounted for variables such as job strain, age, sex, education level, occupation, smoking status, body mass index and other health factors.

"The link between long working hours and high blood pressure in the study was about the same for men as for women," Trudel said. "People should be aware that long work hours might affect their heart health, and if they're working long hours, they should ask their doctors about checking their blood pressure over time with a wearable monitor. Masked hypertension can affect someone for a long period of time and is associated, in the long term, with an increased risk of developing cardiovascular disease."