You asked

Please could you supply me with data as to the number of employee sick days taken and their reasons between 2008 to 2018, for employees aged 18 and over?

We said

Thank you for your request.

We hold some information on sickness absence in the UK labour market which includes information on the number of days lost, with the reasons for sickness absence. The latest version of the release was published in July 2018, with data up to and including 2017. The main analysis includes all people in employment, but within the analysis it includes a split between employees and self-employed. The analysis is based on those aged 16 years and over, rather than aged 18 and over;

The release of the data was also accompanied by a short article;