PARIS (AFP) -- The mental health of asylum-seekers worsens dramatically if they are detained and many plunge into a deep depression, according to a U.S. study published on Saturday in ***The Lancet***, the British medical weekly.

The research is based on symptoms described by 70 asylum-seekers detained in New York, New Jersey and Pennsylvania.

The United States has around 5,000 detained asylum-seekers, according to the authors, led by Allen Keller, assistant professor of medicine at New York University School of Medicine.

These individuals are often held in detention for months or years pending a decision on their asylum claim. They have to wear prison clothes and if they are taken out of jail have to be shackled.

Anxiety, depression and post-traumatic stress disorder worsen significantly the longer the person is detained, according to the research.