Some 400,000 people in the Netherlands have type 2 diabetes without being aware of it, a study of health data on behalf of diabetes charity Diabetesfonds has shown, prompting calls for a national screening.

The Dutch Cohort Consortium, which pools data from universities and other institutions, looked at data from some 200,000 people who are part of a group of over 400,000 whose health has been monitored for the last 25 years.

The research makes it clear that one in three people has the disease without knowing about it. “Type 2 diabetes is often called the hidden killer because it develops very slowly and the initial symptoms are vague, such as urinating more often, tiredness or worsening eyesight,” Diena Halbertsma, director of the Diabetesfonds, told broadcaster NOS.

Untreated, high glucose levels can cause irreversible damage to the heart and kidneys and increase the risk of dementia in the long term.

Early detection is key, Halbertsma said because medication can prevent complications. A healthy lifestyle with more exercise, healthier food and less stress also helps, she said.

The Diabetesfonds calls on people to do the diabetes risk test on its website. It also wants a national screening for type 2 diabetes. “We want the government to invest more in early diagnosis and prevention and promote healthy living, which will prevent many cases of type 2 diabetes,” Halbertsma said.