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People who work 55 hours or more per week have a 33% greater risk of stroke and a 13% greater risk of coronary heart disease.

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There are some doubters but intuitively this makes sense.

People who work 55 hours or more per week have a 33 percent greater risk of stroke and a 13 percent greater risk of coronary heart disease than those working standard hours, researchers reported on Wednesday.

The new analysis includes data on more than 600,000 individuals in Europe, the United States and Australia, and is the largest study thus far of the relationship between working hours and cardiovascular health. But the analysis was not designed to draw conclusions about what caused the increased risk and could not account for all relevant confounding factors.

“Earlier studies have pointed to heart attacks as a risk of long working hours, but not stroke,” said Dr. Urban Janlert, a professor of public health at Umea University in Sweden, who wrote an accompanying editorial. “That’s surprising.”

Mika Kivimaki, a professor of epidemiology at University College London, and his colleagues combined the results of multiple studies and tried to account for factors that might skew the results. In addition to culling data from published studies, the researchers also compiled unpublished information from public databases and asked authors of previous work for additional data.

Dr. Steven Nissen, the chief of cardiovascular medicine at the Cleveland Clinic, found the methodology unconvincing. “It’s based upon exclusively observational studies, many of which were unpublished,” and some never peer-reviewed, he said.

Seventeen studies of stroke included 528,908 men and women who were tracked on average 7.2 years. Some 1,722 nonfatal and deadly strokes were recorded. After controlling for smoking, physical activity and high blood pressure and cholesterol, the researchers found a one-third greater risk of stroke among those workers who reported logging 55 or more hours weekly, compared with those who reported working the standard 35 to 40 hours.

While the increase in risk for each individual was slight, experts said the effect was noteworthy in a large population in which many people are working long hours.

In his editorial, Dr. Janlert said, “Long working hours are not a negligible occurrence.” Full-time American workers in nonagricultural industries labor for an average 42.5 hours per week, according to Bureau of Labor Statistics.

But workweek hours vary sharply depending on occupation and company culture. In Gallup surveys in 2013 and 2014, nearly four in 10 full-time American workers reported laboring at least 50 hours weekly, and half said they usually work more than 40 hours.

Dr. Kivimaki and his colleagues also found the risk of stroke increased as work hours lengthened. But he said, “we found no differences between men and women, or between older people and younger ones, or those with higher or lower socioeconomic status.”

Dr. Ralph Sacco, a former president of the American Heart Association, said, “The consistency of the findings across published and unpublished data — that alignment is a strength and makes this more convincing.”

The analysis of coronary heart disease among workers included 25 studies involving 603,838 people. (Some of these studies were also used in the stroke analysis.) After a mean of 8.5 years, 4,768 had received diagnoses of heart disease as a cause of death or hospitalization. The researchers accounted for age, sex and socioeconomic status.

Dr. Stephen L. Kopecky, a professor of medicine in the division of cardiology at the Mayo Clinic, said that this analysis did not fully account for the effects of cholesterol, family history and blood pressure in all cases, so it is possible that long hours are not entirely to blame.

Furthermore, he argued, it matters to stroke risk whether an employee has a job with high demands and little control, which researchers call “job strain.”

“You have higher blood pressure when you have job strain,” Dr. Kopecky said. “And guess what that’s associated with? Stroke.”

Source is this peer reviewed article:

I'm not sure I understand what Kopecky's rationale is for his doubts. Like... basically he thinks it all comes down to blood pressure so why even look at hours worked? Personally I suspect there are a lot of different causes of high blood pressure and they are not equal in how easy they are to fix. For instance, blood pressure rises as people get older because their arteries are hardening; but it's relatively easy to get the arteries to relax, and also many cardiologists don't worry about it as much because let's face it hypertension in an 80 year old isn't the crisis that it is in a 30 year old. On the other hand, obesity-linked hypertension... it's super easy for your doctor to tell you to lose weight but the evidence suggests that 99% of people cannot do so permanently. Seems a little reductive for a doctor to say "job strain is just one cause of high blood pressure, no different than any other cause."

I agree with you.

If Kopecky's argument is the best the NYT could find against this result, then the result seems pretty solid to me: Working too much increases likelihood of stroke.

I liked Dustin Moskovitz's recent Medium post Work Hard, Live Well. In it he states that not only is it NOT that case that you have to overwork employees to succeed, but that allowing them to have a good work-life balance is actually better for the company.

The research is clear: beyond ~40–50 hours per week, the marginal returns from additional work decrease rapidly and quickly become negative. We have also demonstrated that though you can get more output for a few weeks during “crunch time” you still ultimately pay for it later when people inevitably need to recover. If you try to sustain crunch time for longer than that, you are merely creating the illusion of increased velocity. This is true at multiple levels of abstraction: the hours worked per week, the number of consecutive minutes of focus vs. rest time in a given session, and the amount of vacation days you take in a year.

Rest matters.

Great article. I watched Dustin defend it yesterday in this comment thread:

I think he's right. There's a thing he calls "energy debt" that needs to be repaid.

He wishes he had slept more when he was younger. 

I'm hoping that the association between long work hours and stroke/cardio vascular disease is more related to the fact that often those working long hour are not eating healthfully.  If that were the case I wouldn't have to worry about working long hours as long as I'm careful to eat well.

"After controlling for smoking, physical activity and high blood pressure and cholesterol..."

Sounds like they controlled for neither eating well nor sleeping habits. 

Would be interesting to see the same data controlled for eating, sleeping, stress level of job, stress level of home, # of jobs. 

Yes it would. I believe further studies are coming but they cannot come fast enough!

Especially for entrepreneurs who work 55+ hours!

Beth you know it!

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