Scientists have found evidence that supports claims of the healing power of laughter, which appears to help to keep the heart beating strongly by improving arterial blood flow.

Researchers in the United States asked 20 healthy young adults to watch segments between 15 and 30 minutes long of sad films and humorous films, a minimum of 48 hours apart.

Examples of sad or upsetting footage used in the small study, published in the journal Heart, include the opening scene of the war film Saving Private Ryan, while comic excerpts were taken from films such as There’s Something About Mary.

Participants were asked not to drink alcohol, use vitamins or herbs or take aerobic exercise the evening before the experiment — all factors that can affect blood flow.

A total of 160 measurements of brachial artery blood flow were taken before and one minute after phases of laughter or sadness. The brachial artery runs from the shoulder to the elbow, and is a good indicator of blood flow.

Brachial artery blood flow was reduced in 14 of the 20 participants after watching film clips that caused distress. But it was increased in 19 of the 20 participants after watching clips that elicited laughter.

The difference in flow between responses that caused mental stress and those that encouraged laughter was found to exceed 50 per cent.

Recent studies have indicated that stress-inducing factors such as depression and anger may contribute to coronary heart disease. But very little research has been done on the impact of positive emotions.

Michael Miller, a cardiologist from the University of Maryland Medical Centre, said: “The extent of the impact of watching a sad film was of the same magnitude as remembering episodes of anger and doing mental arithmetic. The impact of watching a funny film was equivalent to a bout of aerobic exercise or starting on statin treatment.”

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