We know that eating healthy food, exercising, not smoking, and limiting drinking are all effective ways to prolong your life.

But there's a new factor you might want to take into account – the amount of holidays you take.

A new study, by researchers from the University of Helsinki, Finland, investigates the health of 1,222 middle-aged men who took part in the Helsinki Businessmen Study.

Back in 1974 and 1975, the Businessmen Study recruited middle-age male executives born between 1919 and 1934.

The study was actually looking at blood pressure and mortality, and all the men had at least one risk factor for cardiovascular disease. But the participants were also asked to record whether and when they were going on vacations.

Back in 1974, the men were randomised into two groups: 610 controls, and 612 intervention participants, for five whole years. The intervention group was given advice to eat healthy food, reach a healthy weight, and do physical activity.

If these things weren't effective to lower the men's cardiovascular disease risk, they were also prescribed blood pressure medication.

The men in the control group were told to go about their business as usual, with no health or lifestyle interventions offered to them.

When the 5-year study ended, the team did a follow-up 15 years later in 1989, and a 40 year follow-up in 2014.

At the end of the study, the researchers found the risk of cardiovascular disease was reduced in the intervention group compared to the controls, but 15 years later, there'd actually been more deaths in the intervention group.

Now, 40 years later, the death rates have started to even out again. To discover why this might be, the team took a closer look into other data that was part of the study, to work out what was going on, and ended up finding a weird result.

"The harm caused by the intensive lifestyle regime was concentrated in a subgroup of men with shorter yearly vacation time," explains one of the researchers, Timo Strandberg.

"In our study, men with shorter vacations worked more and slept less than those who took longer vacations. This stressful lifestyle may have overruled any benefit of the intervention."

Vacation time had no impact on risk of death in the control group, but in the intervention group, the difference was staggering.

Men who took three weeks or less of annual vacation had a 37 percent increased chance of dying compared with those that took over three weeks of holidays.

"We think the intervention itself may also have had an adverse psychological effect on these men by adding stress to their lives," Strandberg adds.

It's important to note though that this study is old – the research was happening in the 1970s. Now, as part of cardiovascular disease risk, people include stress management, and we also have better medication for heart issues. 

But it's still an important reminder that a stressful job with few holidays could be doing more than just making you feel tense.

"Vacations can be a good way to relieve stress," says Strandberg.

"Don't think having an otherwise healthy lifestyle will compensate for working too hard and not taking holidays."

The research has been accepted for publication in The Journal of Nutrition, Health & Aging.