More than one in five pensioners in Germany could find themselves threatened by poverty in two decades time, according to a study by the German Institute for Economic Research (DIW).

The study found that the number of pensioners facing a risk of poverty by 2039 could rise from 16.8% at current levels to 21.6%.

Authors of the investigation, released Thursday by the Germany-based Bertelsmann Foundation, said they expected an improvement in the employment market over the next 20 years. However, they added, certain groups — such as the long-term unemployed, single people and those with low qualifications — were less likely to benefit.

"Even with positive developments in the labor market, we have to be ready for a significant increase in poverty among the elderly in the next 20 years," said study lead author Christof Schiller.

Individuals at risk of falling into poverty were defined as those receiving less than 60% of the average income. According to the study, this equated to an income of less than €905 ($997) per month.