A 60- to 80-hour workweek is a badge of honor for some professionals, but such a brutal schedule is unhealthy for them and their companies alike.

If you and your employees work 80 hours a week, that means you have a severely limited amount of non-work time. Simply put, it is not enough time for you and your employees to sleep, have a personal life, and recharge so you can get back to work ready to perform.

Sarah Green Carmichael, a senior associate editor at Harvard Business Review, writes about the toll that's taken on overworked employees. "The story of overwork is literally a story of diminishing returns," Carmichael writes. According to a group of studies, overworked employees are not as productive as ones with predictable hours and time off.

The business world has already had a sense of this for quite some time.  When, decades ago, labor unions successfully made factory owners shorten workdays, it resulted in an increase in employee output and a decline in mistakes and accidents.

In 2008, Harvard Business School's Leslie Perlow and Jessica Porter experimented with reducing work hours for employees at Boston Consulting Group, and the findings were the same--cutting hours and imposing required time off increased productivity.

If you need more evidence before reconsidering your schedule and culture, take a look at some of the more devastating effects chronic long work hours can have on your employees and your company.

More hours doesn't equal more results.

The basic reason for working longer hours is, of course, to increase output. But again, research finds that's not the actual result. Carmichael cites a study of consultants conducted by Boston University professor Erin Reid, in which "managers could not tell the difference between employees who actually worked 80 hours a week and those who just pretended to." 

Overworked employees are unhealthy employees.

The culture of overwork doesn't just hurt performance, it hurts individuals. If your employees work 65 to 80 hours a week, what time do they have for their families and for their mental and physical health? Marianna Virtanen, a research professor at the Finnish Institute of Occupational Health, found in numerous studies that being overworked can lead to serious health problems, including substance abuse, depression, diabetes, and heart disease. Another of Virtanen's studies found that employees who work long hours are 12 percent more likely to become heavy drinkers compared with colleagues who log shorter hours. And in a decades-long study of British civil servants, the Whitehall II study, workers who clocked more than 55 hours a week were found to accelerate "aging-related decline in memory and thinking skills."

An overworked workforce hurts the company.

Because chronically overworked employees are unhealthy employees, long hours negatively affect the company's bottom line. According to the American Institute of Stress, about 60 percent of doctor visits are because of stress-related health issues, resulting in American businesses losing $300 billion each year to "lowered productivity, absenteeism, health-care, and related costs stemming from stress." Overworked employees also account for increased health insurance costs. "Even the Scroogiest of employers, who cared nothing for his employees' well-being, should find strong evidence here that there are real, balance-sheet costs incurred when employees log crazy hours," Carmichael writes.