As many as 50,000 Welsh employees were on sick leave for a month or more each year between October 2010 and September 2013, according to new figures.
The Department of Work and Pensions has published the stats as it prepares to launch a new Health and Work service in a bid to prevent sickness absence turning into long-term welfare dependency.
The service aims to help employees who have been on sickness absence for four weeks to return to work and support employers to manage sick absence among their workforce.
Work and Pensions minister Mike Penning said: "More than 130 million years a day are lost to sickness absence in Great Britain, which has a substantial impact on workers, employers and taxpayers.
"As part of the government's long-term economic plan, we are taking action to get people back into work. This is a triple-win. It will mean more people with a job, reduced cost for business, and a more financially secure future for Britain."
Hundreds of benefit claimants across Wales will see their payments capped at £500 a week from today. New rules by the UK government mean families can no longer claim more - and single people will be limited to £350 a week.
Most will see a reduction in their housing allowance meaning they'll have to move or make-up the shortfall. The government says no-one should receive more in benefits than those working. The majority of those affected in Wales will be in Cardiff - where an estimated 300 people will see a cut.