In this study, we found an association between lack of physical activity and shorter TL in a large cross-sectional sample of breast cancer survivors. Adjusting for the impact of age, women reporting no physical activity had significantly shorter TL than women who reported engaging in moderate to vigorous activity. The mean difference between women who were and were not physically active was 270 bp. Research by Slagboom et al. demonstrated that the average decrease in TL was 31 bp per year [16]. This suggests that, independent of age, more sedentary women may be close to 9 years biologically older than women who are more physically active, on a cellular level. To our knowledge, this is the first study to quantify the relationship between physical activity and TL in breast cancer survivors.
Telomere length measured from PBMCs reflects the cumulative effects of psychosocial, environmental and behavioral factors, as opposed to current health status, and is predictive of morbidity and mortality [17]. The presence of short TL in peripheral blood cells has been linked to age-related disease and preclinical conditions of diseases including increased mortality from cancer [18]. A recent longitudinal cohort study of 478 women with stage I to IIIa breast cancer examined PBMC TL change from 6 to 30 months post diagnosis [19]. Telomere shortening was associated with increased risk of all cause and breast cancer specific mortality, suggesting that change in blood TL over time could be a biomarker of prognosis. This finding is consistent with an earlier prospective 20-year study of 47,102 individuals suggesting that shorter TL is associated with reduced survival after all cancer diagnoses, including breast [20]. Based on existing research linking TL measured in PBMC and increased mortality from cancer, TL may represent an innovative biomarker to measure the status of host biology of aging; and as the host ages, its ability to perform immune surveillance may decrease, and thereby increase the probability of recurrence of metastasis.