Diet, physical activity, all-cause and cause-specific mortality: repeated measures considerations.

The study aimed to explore the impact of using a single baseline measure versus repeated exposure measures on the independent and joint associations of diet and physical activity with mortality risk. We analyzed 106,387 adults from the Nurses' Health Study and Health Professionals Follow-up Study (1990-2020), with a 4-year lag applied between exposure assessment and time at risk of death using multivariable Cox proportional hazards models. Cumulative averages of the Alternative Healthy Eating Index (AHEI) and moderate-to-vigorous physical activity (MVPA) were calculated from up to 15 repeated measures. Outcomes were all-cause mortality, cardiovascular disease (CVD) mortality, and physical activity, diet, and adiposity-related (PDAR) cancer mortality. During a median follow-up of 29.3 years, 50,844 deaths occurred. Higher AHEI and MVPA (multivariable-adjusted HR [95% CI] comparing the 90th to the 10th percentile for each, respectively) were associated with lower risks of all-cause mortality (0.82 [0.80, 0.84]; 0.78 [0.77, 0.80]); CVD mortality (0.88 [0.84, 0.92]; 0.72 [0.69, 0.76]) and PDAR cancer mortality (0.87 [0.80, 0.94]; 0.88 [0.82, 0.95]). The greatest risk reductions in all-cause (38%), CVD (41%), and PDAR cancer mortality (29%) were observed in the highest AHEI and MVPA categories combined versus the lowest. The strongest inverse associations for MVPA were observed when AHEI was low, and the strongest inverse associations for AHEI were seen when MVPA was low. All associations were substantially attenuated when using single baseline measures instead of cumulative averages. Both diet and MVPA contribute to the lowest mortality risk, which is observed most clearly using repeated measures.