Drs Birkhofer, Schmidt, and Förstl astutely point out that participants with depression were younger than participants without depression in our study (mean age, 62 vs 68 years; P<.0001).1 We agree that age has a well-documented effect on HRV and deserves particular attention. Although we entered age in all of our multivariable models, age was not associated with any measures of HRV in our sample, with the exception of wideband-frequency power. When we performed the requested analyses adjusted by age, we still found no difference in HRV between participants with and without depression (Table). Likewise, there was no difference in age-adjusted mean HRV between participants with severe depression and participants without depression (all P values >.10). Finally, we found no evidence of an interaction between age and depression in predicting HRV (all P values for interaction >.10). Thus, age was not a confounding factor in our sample.
Gehi A, Whooley M. Heart Rate Variability and Depression—Reply. Arch Gen Psychiatry. 2006;63(9):1052. doi:10.1001/archpsyc.63.9.1052-b