1. Section of Gerontology and Geriatrics, Department of Internal Medicine, Leiden University Medical Center, Leiden, the Netherlands
2. Leyden Academy on Vitality and Ageing, Leiden, the Netherlands
3. Division of Geriatric Research, Department of Internal Medicine, Southern Illinois University School of Medicine, Springfield, IL 62794-9628, USA
4. Paul F. Glenn Laboratory, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
5. Department of Biology, University of Alabama at Birmingham, Birmingham, AL 35294, USA