By Jane Kirby, PA Health Editor Exercising twice a week or more significantly cuts the risk of insomnia, according to a long-term study. People who do regular exercise are 42% less likely to have difficulty falling asleep than those who are inactive, and are 22% less likely to report any symptoms of insomnia. The research, published in the journal BMJ Open, also found that people who kept exercising in the long term were significantly (55%) more likely to be normal sleepers (six to nine hours a night) than those who did not exercise. They were also significantly less likely (29%) to be short s…