Researchers asked 20 healthy young adults to watch 15 to 30 minute segments of sad and humorous films, a minimum of 48 hours apart.
Examples of sad films included the opening scene of Saving Private Ryan and examples of comedy films included There's Something About Mary.
Participants were asked to abstain from drinking alcohol, using vitamins or herbs, or taking aerobic exercise the evening before the experiment, as all these can affect blood flow.
In all, 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 around the body.
Brachial artery blood flow was reduced in 14 of the 20 participants after watching movie clips that caused distress. But it was increased in 19 of the 20 participants after watching movie clips that elicited laughter. The difference in flow between sad and happy responses exceeded 50 per cent.
The extent of the impact of watching a sad film was of the same magnitude as remembering episodes of anger and doing mental arithmetic, say the authors, while the impact of watching a funny film was equivalent to a bout of aerobic exercise or starting on statin treatment.