Telomere length, a reliable predictor of disease pathogenesis, can be affected 
by genetics, chronic stress and health behaviors. Cross-sectionally, highly 
stressed postmenopausal women have shorter telomeres, but only if they are 
inactive. However, no studies have prospectively examined telomere length change 
over a short period, and if rate of attrition is affected by naturalistic 
factors such as stress and engagement in healthy behaviors, including diet, 
exercise, and sleep. Here we followed healthy women over 1 year to test if major 
stressors that occurred over the year predicted telomere shortening, and whether 
engaging in healthy behaviors during this period mitigates this effect. In 239 
postmenopausal, non-smoking, disease-free women, accumulation of major life 
stressors across a 1-year period predicted telomere attrition over the same 
period-for every major life stressor that occurred during the year, there was a 
significantly greater decline in telomere length over the year of 35 bp 
(P<0.05). Yet, these effects were moderated by health behaviors (interaction 
B=0.19, P=0.04). Women who maintained relatively higher levels of health 
behaviors (1 s.d. above the mean) appeared to be protected when exposed to 
stress. This finding has implications for understanding malleability of telomere 
length, as well as expectations for possible intervention effects. This is the 
first study to identify predictors of telomere length change over the short 
period of a year.