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A chronic illness can bring plenty of worries, particularly about what the future holds. But starting an exercise program can help curb that anxiety, a new review finds.

In this week's Archives of Internal Medicine is a review of how exercise affects anxiety. After combing through 40 studies on the topic, the reviewers say they found "solid evidence" that exercise can curb anxiety in patients dealing with a chronic illness – even those illnesses that can make it difficult to exercise, such as COPD and heart disease.

Anxiety is common among people who are dealing with a chronic illness as patients deal with questions such as: will my condition worsen? What will this illness take away from me? Is this going to kill me?

"Anxiety symptoms and disorders are common among individuals with a chronic illness, yet health care providers often fail to recognize or treat anxiety and may consider it to be an unimportant response to a chronic illness," write the reviewers, led by Matthew P. Herring, a doctoral student in the department of kinesiology at the University of Georgia in Athens.

Yet, worried patients may be less likely to take their medications and follow their doctor's advice, the authors point out. Their anxiety also reduces their quality of life and often leads them to make unnecessary visits to their doctor or specialist.

While there are effective anti-anxiety drugs available, exercise can be an effective -- and cheap -- alternative, Herring and colleagues found.

Herring and his team analyzed data from 40 studies on how exercise affects anxiety, involving a total of 3,000 study volunteers. All of the participants were sedentary, had chronic illnesses, but were still able to exercise in sessions of at least 30 minutes. The illnesses included:

• heart disease
• fibromyalgia
• multiple sclerosis
• psychological disorders
• cancer
• chronic obstructive pulmonary disease
• chronic pain such as knee osteoarthritis and back pain

They found that compared with people with similar conditions who didn't exercise, those who did exercise had a 20 per cent reduction in anxiety symptoms.

And they found that it didn't matter how they exercised or how vigorously; the participants all reported they felt less worried, apprehensive and nervous.

"We found that exercise seems to work with just about everybody under most situations," Pat O'Connor, a co-author of the paper and professor at the University of Georgia, said in a news release. "Exercise even helps people who are not very anxious to begin with become more calm."

Multiple sclerosis was the only condition in which exercise did not appear to have a significant effect.

Exercise sessions that lasted longer than 30 minutes were better at reducing anxiety than shorter sessions, the researchers found. But surprisingly, they found that exercise programs that lasted longer than 12 weeks appeared to be less effective at reducing anxiety than those that lasted three to 12 weeks long.

The researchers think that might be because study participants were less likely to stick with the longer exercise programs, suggesting that being able to complete the whole program brought more satisfaction and resulted in greater reductions in anxiety.

"Because not all study participants completed every exercise session, the effect of exercise on anxiety reported in our study may be underestimated," said study co-author Rod Dishman, a UGA professor of kinesiology.

"Regardless, our work supports the use of exercise to treat a variety of physical and mental health conditions, with less risk of adverse events than medication."