New research from Mayo Clinic experts shows that you’re more likely to die of a heart attack at night or on the weekend.

The scientists reviewed nearly 50 studies involving 1,896,859 patients that showed that being treated at the hospital for a heart attack during off-hours, such as nights and weekends, was associated with a 5% greater risk of dying–both in the hospital and after discharge–than being treated during regular hours.

For patients with a severe form of heart attack, called ST elevation myocardial infarction (STEMI), off-hour treatment resulted in delays of about 15 minutes, which increased the risk of death by about 10% to 15%. The researchers suspect that the skeleton staff, and not having specialists on hand in the hospital, are the main reasons for the higher death rates.

It’s not the first study to highlight the problem, and the connection between when patients get treated and health outcomes has recently received more attention, since they reveal areas in which hospitals can improve on the care they deliver. Another study from May 2013 involving one million hospital admissions for heart failure over a 14 year period found that patients who were admitted to hospitals for heart failure in January, on a Friday or at night, spent more time in the hospital on average, and had a higher risk of dying from the condition. Other studies found that patients treated in July had higher death rates and complications than those treated in other months, since the most experienced residents graduate in June and the newest crop of residents — last year’s medical students — step in to care for their first patients.

What are hospitals doing anything to address the disparity? “We know that hospitals have fewer staff and resources over nights and weekends which all health professionals know about,” says study author Dr. Atsushi Sorita, a senior fellow in preventive medicine at Mayo Clinic. “There may be an opportunity to design the system to provide consistent quality of care.”

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But simply adding staff may not be the answer. Mayo Clinic in Rochester, Minn. was not one of the hospitals included in the study, but Sorita says it has a 24/7 program in place to treat heart emergencies, with specialists and well-trained nurses available any time of day or night. Has it made a difference? Sorita says the round-the-clock heart failure care has been in place since around 2008, but there are still fewer staff members and resources over the nights and weekends. “We can’t conclude from this study [if adding a full staff will have an impact], but increasing staff would add costs to the hospital, and how much value can we add? We can’t conclude from our study,” he says.

Dr. Gregg Fonarow, the co-director of the UCLA Preventative Cardiology Program and an American Heart Association spokesperson, says healthcare providers should be paying more attention to how much and what type of staffing is enough to address the mortality differences. “Providers should continue to work to enhance the healthcare system during regular and off-hours and to reduce existing disparities in cardiac care,” he says in an email to TIME.

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For example, the American Heart Association’s Get With The Guidelines Quality Improvement Program–which was designed to improve in-hospital care based on the latest research–has helped to equalize health outcomes for patients cared for during and outside of normal hours. That program offers doctors access to research studies, professional workshops and webinars on best practices that can improve their patients’ outcomes, as well as education materials for patients to help them make quick recoveries. “[This illustrates] that performance improvement systems can bridge this gap in care and outcomes for acute myocardial infarction patients presenting during off-hours,” Fonarow says in his email.

The latest study isn’t a message that people who need emergency heart treatments avoid the hospital if it’s at night or on a weekend. It’s a wake up call to administrators that there are serious discrepancies in health outcomes that are within their control to eliminate — by making sure that the care provided is of the highest quality no matter what the day or time of day.

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