Author Affiliations: Foundation of Public Health, Mutuelle Generale de l’Education Nationale, Paris, France (Dr Vercambre); and Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School (Drs Vercambre, Grodstein, and Kang), and Department of Epidemiology, Harvard School of Public Health (Drs Grodstein and Kang), Boston, Massachusetts.
We thank Dr Smith for his interest in our study. Dr Smith is correct that our study was an observational study and not an intervention study, that our analyses did not adjust for dietary patterns, and that we used a telephone cognitive assessment.
We fully acknowledge the observational nature of our study, which only permits the evaluation of associations and is not causal evidence. We were careful throughout the text to state that we observed strong associations between physical activity and cognitive health and that our findings need confirmation in future studies. However, as Smith and colleagues1(p248) state in the largest meta-analysis of clinical trials of physical activity and cognition to date, randomized controlled trials “are limited by logistical constraints in their ability to sustain interventions over prolonged periods of time.” Thus, our observational study, which has evaluated the association between average physical activity over a year and long-term cognitive decline occurring 3.5 years later among 2809 women, provides important data to address the gap in the clinical trial literature.
Vercambre M, Grodstein F, Kang JH. Physical Activity, Vascular Health, and Cognitive Impairment—Reply. Arch Intern Med. 2012;172(1):83-84. doi:10.1001/archinternmed.2011.617