A new Harvard poll finds many workers are suffering with chronic conditions but haven’t told their boss.

The survey found 58% of employees have conditions like heart disease, diabetes, asthma, and hypertension. Three-quarters of them manage their conditions during work hours, but 60% have not told their employers about their health problems.

More than a third of them have delayed medical care so they wouldn’t miss work.

The researchers say the secrecy is taking a toll on workers’ lives and productivity.