Northern Amalgamated Workers Union Rotorua representative Robert Popata said the annual sick leave bill would only go up.
"The workforce is a very ageing workforce at the moment. It's pretty hard to say that 40 and 50-year-olds are bucking the system.
"The fact is, the older we get ... we get sick."
Sick employees whose sick leave entitlement had run out were showing up for work despite genuine illness, battling through because wages were so low they could not afford unpaid time off, he said.
Suggestions workers were pulling sickies out a sense of entitlement were "absolute rubbish", he said.
"The boss can actually go to the doctors [for verification] themselves. So if they think that [employees] are playing up they have a right to get a second opinion."
The study was done by BusinessNZ, Southern Cross and injury management provider Gallagher Bassett, and looked at 2012 data from 113 businesses and public sector entities, employing more than 97,000 workers.
It showed New Zealand workers were off sick less often than those in the UK, where the average was 6.5 days a year.
The median cost of absences for each employee was $837, which included absent workers' salaries, replacement costs and lost productivity.
BusinessNZ chief executive Phil O'Reilly said there was a cost to workers turning up sick, and those genuinely ill should feel supported to stay home.
However, employers could better manage leave for non-illness reasons.
"Rather than take a whole day, if the company says 'I'll give you an hour off to take your kid to the dentist', you'll find employees more satisfied and happy."
Earlier this year, a Medical Council review into how medical certificates were issued sparked renewed debate around employee sick days.