Employees aged between 30 and 49 are more stressed and take significantly more sick leave than their colleagues.
These workers also appear quite disillusioned with their jobs and career path while not taking steps to ensure good health.
The OnePoll survey of 2,000 employees found that more than a third (38%) of those aged 30 to 49 described themselves as stressed all or most of the time, with the main causes being financial worries (43%) pressure from (41%) or worries about (38%) work.
And a similar number (37%) of workers in their thirties said they felt older than their age.
The research, conducted for Axa PPP healthcare, also revealed that 12% had taken the equivalent of a full working week off sick in the last six months - at least twice as much as their younger (5%) or older (6%) colleagues.
This was emphasised by the average amount of time off sick in the past six months hitting 2.3 days, again higher than all other groups.
And a quarter had taken three or four days off sick in that time span.
Axa PPP Healthcare said employers needed recognise that this was a particularly hard hit group "struggling with work and home pressures".
"The research suggests that many are not motivated or feeling valued in their work, an issue we would encourage employers to proactively address as the 30-49 age group are likely to have at least 20 years left in the workplace. Employers need to support their workers' mental and physical health, offering positive steps to ensure wellbeing now will help to ensure resilience in future."
Other key findings included: