1. Regular consumption of nuts was associated with lower overall and cause-specific mortality.
2. The association was dose-dependent, with higher frequency of nut consumption associated with lower hazard ratios for death.
Evidence Rating Level: 2 (Good)
Study Rundown: This study of two large, prospective cohorts demonstrated an association between nut consumption and mortality. The study found an inverse association between nut consumption and overall as well as cause-specific mortality. The effect was dose-dependent, with higher frequency of nut consumption associated with lower hazard ratios for death. The authors caution that they could not rule out all confounding factors, and that the study design allows for conclusions on association but not causality. Nevertheless, the study was well-designed and adequately powered due to the large study size, long follow-up period, and high follow-up rates in both cohorts.
The study was funded by the NIH and the International Tree Nut Council Nutrition Research and Education Foundation.
In-Depth [cohort study]: This study assessed the association between nut consumption and mortality. The final analyses included 76,464 women and 42,498 men after exclusions. Study subjects were followed for a period of 30 years (2,135,482 person-years). The primary outcome was death from any cause. Cause-specific mortality was also analyzed.
Pooled, multivariate hazard ratios for death for nut consumers compared to non-consumers were 0.93 (95% confidence interval [CI], 0.90 to 0.96) for nut consumption less than once per week, 0.89 (95% CI, 0.86 to 0.93) for once per week, 0.87 (95% CI, 0.83 to 0.90) for two to four times per week, 0.85 (95% CI, 0.79 to 0.91) for five or six times per week, and 0.80 (95% CI, 0.73 to 0.86) for seven or more times per week (P<0.001 for trend). Similar patterns were observed in both men and women.
In cause-specific analyses, significant inverse associations were observed for death due to cancer, heart disease and respiratory disease. For any nut consumption, the hazard ratio was 0.91 (95% CI, 0.85 to 0.97) for death due to cancer, 0.74 (95% CI, 0.68 to 0.81) for heart disease, and 0.81 (95% CI, 0.65 to 1.01) for respiratory disease.
The authors could not rule out the possibility of confounding by unknown factors, but believed that based on sensitivity analysis, it was unlikely for one strong confounding factor to fully account for the associations.
By Xiaozhou Liu and Adrienne Cheung
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