Author Affiliations: Department of Nutrition and Food Hygiene, Soochow University School of Public Health, Suzhou, China (firstname.lastname@example.org).
To the Editor: Pooling data from 28 prospective cohort studies comprising more than 300 000 adults, Dr Pan and colleagues found that depression was associated with a 45% increased risk of developing stroke, leading them to conclude that “depression is a significant risk factor for stroke.”1
However, the possibility of reverse causality (depression could be the consequence rather than the cause of stroke) needs to be addressed. Pan et al1 included 7 studies that enrolled baseline stroke cases, which accounted for nearly 20% of the total weight. Although their sensitivity analysis excluding these studies yielded similar results, it remains possible that subclinical stroke may have caused depression.2 If that is the case, treating depression might have little effect on stroke prevention. In addition, reverse causality is also suggested by the increased risk in studies with shorter follow-up.1
Dong J. Depression and Risk of Stroke. JAMA. 2011;306(23):2562-2563. doi:10.1001/jama.2011.1840