Hundreds of airline pilots – potentially even thousands – are so depressed they are having thoughts of suicide or self-harm, a new study suggests.

Academics from Harvard University in the US carried out an anonymous survey of pilots after Andreas Lubitz, the depressed co-pilot of Germanwings plane deliberately flew it into a mountain, killing 149 people, last year.

Some 4.1 per cent reported having “thoughts of being better off dead or self-harm within the past two weeks”, according to a paper in the journal Environmental Health.

If this is an accurate reflection of the extent of the problem generally, it would mean that more than 5,700 out of a total of about 140,000 airline pilots worldwide feel like this.

The study comes as British Airways cabin crew voted for strike action, with the Unite union saying many were unfit to fly because of “stress and depression”.

In the Environmental Health paper, the researchers said their key findings were “surprising”. “Hundreds of pilots currently flying are managing depression, and even suicidal thoughts, without the possibility of treatment due to the fear of negative career impacts,” they wrote.

The survey, which involved completing a questionnaire about a number of different subjects including mental health, was made “completely anonymous” to try to get genuine answers from the participants, who came from all over the world.

Out of 1,848 pilots who responded to the section about their mental health, 233 (12.6 per cent) appeared to be depressed.

Some 75 pilots (4.1 per cent) reported “having thoughts of being better off dead or self-harm within the past two weeks”. Of those, 49 had worked as pilots within the past month.

Twenty-four said the problems “made it very or extremely difficult for them to work, take care of home matters, or engage in healthy relationships with people”.

Sexual and verbal harassment of pilots was highlighted by the researchers as a particular problem.

In pictures: Germanwings Airbus A320 plane crash Show all 66 1 /66 In pictures: Germanwings Airbus A320 plane crash In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Flowers are left in front of the monument in homage to the victims of Germanwings Flight 4U 9525 in Le Vernet, southeastern France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Andreas Lubitz was deemed ‘unsuitable for flight duties’ for a period of time during his training with Lufthansa and was receiving regular treatment for depression, sources have claimed as investigators focus their inquiry on his personal life and background In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash People believed to be relatives of the deceased crew on Germanwings flight 4U9525 comfort each other at a reception centre in Le Vernet, France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Rescue workers gather with friends and relatives of those killed onboard Germanwings flight 4U9525 at a reception centre in Le Vernet, France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Flags representing some of the nationalities of the victims are seen as family members and relatives gather near the crash site of an Airbus A320 in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash German and Spain flags symbolizing some of the nationalities of the victims are seen as family members and relatives gather for a ceremony in Le Vernet near the crash site of an Airbus A320 in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Flags symbolizing some of the nationalities of the victims, are seen near the memorial stele in Le Vernet during a ceremony to pay tribute to the victims of an Airbus A320 in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French gendarmes and investigators make their way through debris from wreckage on the mountainside at the crash site of an Airbus A320, near Seyne-les-Alpes In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French gendarmes and investigators work amongst the debris of the Airbus A320 at the site of the crash, near Seyne-les-Alpes, French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French gendarmes and investigators make their way through the debris of the Airbus A320 at the site of the crash near Seyne-les-Alpes, French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Wreckage of the Airbus A320 is seen at the site of the crash, near Seyne-les-Alpes, French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A body of a victim is evacuated by a French Gendarmerie rescue helicopter from the crash site of an Airbus A320, near Seyne-les-Alpes In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Rescue workers recover bodies of victims from the crash site of an Airbus A320, near Seyne-les-Alpes In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French military personnel work amongst the debris of the Airbus A320 at the site of the crash, near Seyne-les-Alpes, French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A helicopter of the French Gendarmerie flies over the crash site of the Germanwings Airbus A320 that crashed in the French Alps, above the town of Seyne-les-Alpes, southeastern France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Search and rescue workers make their way through debris at the crash site of the Germanwings Airbus A320 that crashed in the French Alps, above the town of Seyne-les-Alpes, southeastern France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Flowers and lit candles are placed on the ground in Cologne Bonn airport Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Victims’ relatives join carers outside the school gym in Seyne Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Lufthansa CEO Carsten Spohr, left, and Germanwings CEO Thomas Winkelmann arrive for a press conference near the Germanwings headquarters in Cologne, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Andreas Lubitz, the co-pilot that crashed the Germanwings Airbus A320 in the French Alps Facebook In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Buses loaded with relatives of victims are escorted after their arrival at Marseille airport, southern France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Family and relatives of the victims of the Germanwings plane crash in the Alps are taken on bus to the Prat airport from a hotel in Castelldefels in Barcelona, Spain, to take a Lufthansa flight to visit the crash site in Seyne les Alps in France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash An Airbus plane of German airline Lufthansa carrying onboard relatives of the Germanwings plane crash victims takes off from the Duesseldorf airport in Duesseldorf, western Germany, en route to Marseille In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A Germanwings employee places flowers in commemoration of the victims of the Germanwings plane crash in the French Alps, at the airport in Duesseldorf, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Members of German Government Chancellor Angela Merkel, Vice Chancellor and Economy Minister Sigmar Gabriel and Foreign Minister Frank-Walter Steinmeier, from right, hold a minute of silence to commemorate the victims of the Germanwings plane crash in the French Alps at the parliament Bundestag in Berlin, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Realtives of passengers of the Germanwings airliner that crashed in the French Alps leave the Gran Hotel Rey Don Jaime towards Barcelona El Prat airport where a lufthansa plane will fly to Marseille, in Barcelona, Spain In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Olivier Cousin (R), director of the mountain rescue team, which is responsible for the safety of the emergency workers on site, gives an interview in Seyne Les Alpes, France In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Alpine climbers take off in a police helicopter in Seyne Les Alpes In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash German Chancellor Angela Merkel (L), French President Francois Hollande (C) and Spain's Prime Minister Mariano Rajoy pay respect to victims in front of the mountain in Seyne-les-Alpes, the day after the air crash of a Germanwings Airbus A320 In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A member of the search and rescue personnel stands at the crash site of the Germanwings Airbus A320 in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Search and rescue personnel at the crash site of the Germanwings Airbus A320 in the French Alps Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A sealed container holds black box from the German Airbus operated by Lufthansa's Germanwings budget Airbus A320 crash In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash The voice data recorder of the Germanwings jetliner that crashed in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash The voice data recorder of the Germanwings jetliner that crashed in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Germanwings employees cry as they place flowers and lit candles outside the company headquarters in Cologne Bonn airport In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A student who knew some of the German students involved in a crashed plane, reacts during a minute of silence in front of the council building in Llinars del Valles, near Barcelona, Spain In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Photograph of victims, flowers and candles stand outside the Joseph-Koenig-Gymnasium high school where pupils had gathered to pay tribute to 16 students and two teachers from the school who were on Germanwings flight 4U9525 that crashed yesterday in southern France on March 25, 2015 in Haltern, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Pupils gather at the Joseph-Koenig-Gymnasium high school to pay tribute to 16 students and two teachers from the school who were on Germanwings flight 4U9525 that crashed yesterday in southern France in Haltern, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Students gather in front of the Josef-König secondary school in Haltern am See, western Germany, where some of the Germanwings plane crash victims studied Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A Lufthansa employee signs in a condolence book in Frankfurt, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash The flags of (L-R) Aragon, Spain and the European Union are lowered to half-mast at the Regional Assembly of Aragon in Zaragoza, Spain, as a sign of respect for the victims of the German plane crash in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash The German and the European Union flags hang at half mast in memory of the victims of the plane crash in France in front of the Federal Chancellery in Berlin, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French President François Hollande with Spain’s King Felipe VI and Queen Letizia pay their respects to the victims of the German plane crash in the French Alps Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Debris from the Germanwings Airbus A320 at the crash site in the French Alps above the southeastern town of Seyne Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Search and rescue personnel at the crash site of the Germanwings Airbus A320 in the French Alps Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Wreckage and debris lie on the mountain slopes after the crash of the Germanwings Airbus A320 over the French Alps EPA In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Staff members of Germanwings and Lufthansa hold a candlelight vigil outside their headquarters in Cologne Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A photo provided by the French Gendarmerie shows the crash site in the French Alps In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A rescue helicopter from the French Gendarmerie flies over the French Alps, as day fades into night near to the crash site of the Airbus A320 Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A general view of the crash site of a Germanwings Airbus A320 in the French Alps above Seyne-les-Alpes is pictured in this photo provided by the French Gendarmerie In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Family members of people involved in a crashed plane arrives at the Barcelona airport in Spain AP/Emilio Morenatti In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Rescue helicopters from the French Gendarmerie and the Air Force are seen in front of the French Alps during a rescue operation near to the crash site Reuters In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A helicopter of the French National Gendarmerie is seen in Seyne, south-eastern France, near the site where a Germanwings Airbus A320 crashed in the French Alps ANNE-CHRISTINE POUJOULAT/AFP/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French emergency services workers (back) and members of the French gendarmerie gather in Seyne, south-eastern France, near the site where a Germanwings Airbus A320 crashed in the French Alps BORIS HORVAT/AFP/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash An helicopter of civil security services is seen in Seyne, south-eastern France, near the site where a Germanwings Airbus A320 crashed in the French Alps ANNE-CHRISTINE POUJOULAT/AFP/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Relatives of passangers of the Germanwings plane crashed in French Alps arrive escorted by police officer at Terminal 2 of Barcelona El Prat airport in Barcelona David Ramos/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Relatives of passangers of the Germanwings plane crashed in French Alps arrive at Terminal 2 of Barcelona El Prat airport in Barcelona, Spain David Ramos/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Relatives of passengers killed in Germanwings plane crash arrive at the airport in Duesseldorf, Germany AP/Frank Augstein In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash Police escort a family member of an aircrash victim at Barcelona's El Prat airport LLUIS GENE/AFP/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash French firefighters prepare to take-off in Digne-les-Bains for the crash site of an Airbus A320, in the French Alps REUTERS/Jean-Paul Pelissier In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A family member of a passenger killed in Germanwings plane crash reacts as he arrives at Barcelona's El Prat airport REUTERS/Albert Gea In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash People arrive at a holding area for friends and relatives of passengers on Germanwings flight 4U9525 from Barcelona to Dusseldorf at Dusseldorf International Airport in Dusseldorf, Germany Sascha Steinbach/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash People waiting for flight 4U 9525 are lead away by airport staff at the airport in Duesseldorf, Germany In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A relative (C) of passangers of the Germanwings plane crashed in French Alps arrives at the Terminal 2 of the Barcelona El Prat airport David Ramos/Getty Images In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash A man who appears to have waited for the missing flight 4U 9525 reacts at the airport in Duesseldorf, Germany AP/Frank Augstein In pictures: Germanwings Airbus A320 plane crash Germanwings Airbus A320 plane crash epa04676936 A man looks at a monitor showing a map released on the webpage 'flightradar24 with the exact point where the radar signal of the crashed Airbus A320 aircraft operated by German budget airline 'Germanwings' went missing near Barcelonnette, in the department of Alpes-de-Haute-Provence, in Madrid, Spain EPA

“Female pilots reported more days with poor mental health and having more diagnosed depression than male pilots, which mirrors reporting among the general population,” researchers said.

“The higher prevalence of depression among victims of frequent sexual or verbal harassment in our study provides further evidence of its existence among airline pilots, deep negative effects on its victims, and the urgent need to eliminate this form of harassment and help this subpopulation of workers.”

Dr Rob Hunter, head of flight safety for the British Airline Pilots’ Association, pilots generally had “very good physical and mental health”.

“But, as in all walks of life, some pilots suffer from depression and other mental health issues and the problem applies across many, if not all, safety-critical occupations,” he said.

“The lessons we need to learn from Germanwings, and from this study, are that everyone needs to work to remove the stigma attached to mental health, and that no one should have any fear from discussing it or reporting it.

“Like so many other areas of flight safety, changing the culture is difficult, but necessary. We need to foster an atmosphere or support and understanding, and pilots need to feel able to come forward without fear.”

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Madeleine McGivern, head of workplace wellbeing programmes at mental health charity Mind, said the study showed there was a need for airlines “to regularly assess all pilots’ mental health, so that they can identify any existing health problems and whether these could affect someone’s ability to fly”.

However she added: “Assumptions about risk shouldn't be made across the board for people with depression or any other illness, mental or physical.

“There will be pilots with experience of mental health problems who have flown safely for decades, and assessments should be made on a case by case basis.”

She said attitudes towards mental health could prevent people talking to those closest to them “let alone their employers”.

“It’s vital that all workplaces – including airlines – create an environment where staff feel able to speak about poor mental health, so that measures to support their wellbeing can be put in place,” Ms McGivern said.

“People with mental health problems can and do make a valuable contribution to the workplace, including within the challenging and demanding jobs you’d often associate with the aviation industry.”

Unite claimed that “over two-thirds [of cabin crew] were going to work unfit to fly because they could not afford to be off sick”.

They added that 84 per cent of staff said their financial circumstances since joining BA had caused “stress and depression” and that some have been “sleeping in cars between flights because they could not afford the petrol to get home”.

Unite’s regional officer, Matt Smith, said: “Low pay is a safety issue.”

British Airways said: “Safety is always our priority. We uphold the highest safety standards and meet or exceed all UK, European and International regulations.”