We used PHASE 2.1.1 software (Stephens et al. 2001) to perform statistical inference of haplotypes from our sample data. Only data from fully genotyped subjects, which included 86 octogenarians (25 males) and 101 controls (35 males), were considered. We used the out_pair PHASE output file to assign haplotypes for each individual, with their corresponding probability. Haplotype counts were estimated by obtaining the cumulative probability of each haplotype. In brief, for an individual bearing haplotype A with probability 0.3 and haplotype B with probability 0.7, we added 0.3 and 0.7 to the corresponding counts of haplotypes A and B, respectively, estimating the presence of 0, 1 or 2 copies of a specific haplotype in each individual.

Genomic DNA from controls was extracted from peripheral blood lymphocytes using a KG-Midi extraction kit (Camgen, Cambridge, UK). DNA from octogenarians was obtained from buccal swabs using the BuccalAmp DNA extraction kit (Epicentre). The gene structure of the VDR locus and linkage disequilibrium pattern of populations analyzed are shown in Figure 1.