2017 was a positive year for Sonae's businesses, which continued to grow at a solid pace and made significant progress in the development of their individual strategies. Overall, we evolved further in the development of a portfolio of more autonomous, focused and flexible businesses, ready to perform in the market with high standards of corporate governance, namely as publicly listed companies or integrating strategic partnerships.
Considering the companies we control or co-control, total aggregated turnover increased by 6.3% to 7.6 billion euros and EBITDA also grew, surpassing one billion euros once again.
In retail, turnover increased by 6.8% to 5.6 billion euros, with a positive contribution from all business areas, particularly the food retail business which grew 5.4%, and Worten which exceeded one billion euros in sales with a year-on-year increase above 10%. It is also worth highlighting the performance of online sales that for the first time surpassed 100 million euros.
Sonae Sierra, besides a good operational performance, continued the development of new shopping centre projects, such as Cúcuta in Colombia or the Málaga Designer Outlet, and strengthened its services business area by creating the ORES Socimi fund in partnership with Bankinter.
In a challenging market environment, NOS continued to overcome expectations by improving its competitive position in all market segments, leading in innovation, growing profitability and demonstrating an increasing ability to generate cash flow.
For Sonae Financial Services, this year was marked by a significant growth of the Universo card base, with over 600,000 cards issued in only two years, accounting for 13.2% of total credit card transactions in Portugal in December.
In the retail and telecommunications technology businesses, Sonae IM added value to its portfolio, strengthened its leadership position in the Iberian cybersecurity market and positioned itself as a preferred partner for technology companies with highly innovative projects.
We continue to invest in our growth avenues, particularly in the health and wellness sector, and to create partnerships that enhance the value of our assets, such as the creation of ISRG (Iberian Sports Retail Group) in the sports sector, completed in the beginning of 2018.
The aggregate investment of the companies that we control or co-control reached 726 million euros, of which 316 million euros was invested by fully consolidated companies. The Group's sound operational and financial performance enabled a high level of investment and the maintenance of a steadily growing dividend policy, while reinforcing an already robust capital structure, with a net debt reduction of 8.4% coupled with greater maturity and lower cost of debt.
We are therefore prepared and confident to face future challenges, as we are aware of the quality of our team, the value of our culture and the legacy of Belmiro de Azevedo, which we hold as a reference and which we intend to honour, delivering on our mission of creating economic and social value, taking the benefits of progress and innovation to an ever-increasing number of people.
Ângelo Paupério, Sonae Co-CEO