Gavin Costa was diagnosed with Crohn's disease when he was 18.

While his university friends were enjoying their first taste of freedom, he found it difficult to muster the energy to leave his bed.

The debilitating condition has no cure and the now 68-year-old from Falkirk says at its worst it can "make you a prisoner".

Around one in 200 people in the UK are living with Crohn's and ulcerative colitis, and young people are particularly affected.

Bouts of symptoms can come at random times, known as flare-ups, and there is no clear understanding of what can bring them on.

"The symptoms are many and varied", he says.

"The main one is frequency of going to the toilet for bowel movements, bloody stools when you go to the toilet, pain in the abdomen, very tired, quite often you get a sore back.

"Generally you just feel very, very unwell."

The emotional toll of living with Crohn's is also devastating. Finding out when he was still a teenager, Mr Costa was forced to confront the possibility that it might end his life.

The treatment for the disease was extreme 50 years ago, with surgery to remove large sections of the bowel and fitting a stoma, which creates a hole in the abdomen for faeces and urine.

"If that didn't work there wasn't a great deal of hope after" says Mr Costa.

Luckily there has been a great deal of advancement in the treatment of his illness in the intervening period and he has managed to avoid dangerous surgery while medication keeps him in check.

While in remission, which he has been for a number of years, he says he can almost forget he has the disease, which is well-managed by six tablets a day and a number of other medications.

During serious flare-ups, however, it can be debilitating.

"When you're ill it's impossible - you can't manage it, it manages you.

"You're restricted by what you can do and what the disease allows you to do."

One of the worst ways it impacts sufferers is in a lack of confidence, as regular toilet trips are required.

"You can't go out'" he says.

"When I used to work, I could tell where every toilet in every hotel is in London because I had to know I could get into a toilet within a very short space of time."

He continues: "If you let it, you could become a prisoner because of it when you've got a flare-up."

Now Scots with debilitating bowel conditions are being invited to take part in a study to better understand them.

Researchers in Edinburgh want to shed light on everyday factors that may influence flare-ups of Crohn's disease or ulcerative colitis and investigate how changes in diet and lifestyle might help sufferers.

Mr Costa has decided to sign up in the hope it will lead to another breakthrough in treatment like those that have improved his quality of life in the time he has lived with the illness.

"Over 50 years I've been able to keep one step ahead of the game in terms of the drugs," he says.

"When one drug stopped working another drug had come along. That's because of medical research and trials like this.

"It comes about through people volunteering to actually take part in these trials to prove that these drugs are better than the ones currently in use. I feel by taking part in this study I can give a bit back as well."

The study will collect information from 1500 patients who will be asked to complete online questionnaires about their eating, exercise and sleeping habits and monitor feelings of stress and anxiety.

Called PREdiCCt, (Prognostic effect of environmental factors in Crohn's and colitis), the study is led by Edinburgh University and NHS Lothian and is recruiting patients from Scotland and England.

Dr Charlie Lees is the chief investigator. He says people come in asking what they should do to manage flare-ups and they currently struggle to answer.

"They need medical treatments which work well for a lot of people but there's an urgent need for more treatments better than we have at the moment," he says.

"And all too commonly people come to need surgical interventions where they have parts of their bowel removed.

"People want to do more than take their tablets and get the disease under control. People come to this clinic and ask me what should I do, what should I eat, how should I behave. At the moment we have a total lack of quality data to help answer these questions."

The disease affects many younger people and Dr Lees says the impact can be "devastating".

"The people we typically see are adolescents and young adults, people who are in the prime of their lives, at school, making new interactions with friends, trying to get ahead with their studies or in the workplace and building families.

"And it can be a really devastating effect not even just for that individual but their immediate friends and family, too."