Letter: Obesity link

After reading your article about childhood obesity and lack of sleep (27 May) I wanted to point out that statistical correlations do not always mean that one factor is the cause of the other, but often that both factors have a common cause. Researchers might be interested to look into the question of whether unhappiness or stress might not be the cause of both obesity (compensatory eating to dull feelings) and lack of sleep.

Jenny Martin

Edinburgh