Frequent nut consumption associated with reduced mortality

Bao Y, Han J, Hu FB, et al.
N Engl J Med. 2013 Nov 21;369(21):2001-11. doi: 10.1056/NEJMoa1307352

Background

Nuts are rich in unsaturated fatty acids, fiber, vitamins, minerals and many other bio-active substances, such as phenolic antioxidants and phytosterols [1,2]. Based on observational studies and clinical trials, it has been suggested that nut consumption may be beneficial for coronary heart disease and its intermediate biomarkers such as blood cholesterol [3].
A randomised primary prevention trial in people at high cardiovascular (CV) risk recently showed a significant reduction in major CV events among participants assigned to a Mediterranean diet, one component of which was supplementation with walnuts, hazelnuts or almonds, as compared with a control diet [4].
Nut consumption has also been associated to reductions in various mediators of chronic diseases, including oxidative stress, inflammation, visceral adiposity, hyperglycaemia, insulin resistance and endothelial dysfunction, as well as reduced risk of type 2 diabetes mellitus, the metabolic syndrome, colon cancer, hypertension, gallstone disease, diverticulitis, and death from inflammatory diseases.
Despite these beneficial associations, little information is available on nut consumption in relation to total mortality. This study therefore examined the association between nut consumption and total and cause-specific mortality in two large independent cohort studies of nurses and other health professionals, that provided repeated measures of diet, extensive data on confounding variables,  with 30 years of follow-up. 27000 deaths were observed in the Nurses’ Health Study cohort (121700 females) and the Health Professionals Follow-up Study (HPFS) cohort (51529 males). Dietary intake was measured with the use of validated food-frequency questionnaires administered every 2 to 4 years.

Main results

• Over the study follow-up period, nut consumption was fairly constant. As compared to participants who consumed nuts less frequently, those who consumed nuts more often were leaner, less likely to smoke, more likely to exercise and more likely to use multivitamin supplements: they also consumed more fruits and vegetables and drank more alcohol.
• Pooled data from both cohorts yielded multivariate hazard ratios (HRs) for death for participants who ate nuts, as compared to those who did not eat nuts, of 0.93 (95%CI: 0.90-0.96) for nut consumption less than once per week, HR: 0.89 (95%CI: 0.86-0.93) for once per week, 0.87 (95%CI: 0.83-0.90) for two to four times per week, HR: 0.85 (95%CI: 0.79-0.91) for five or six times per week, and 0.80 (95%CI: 0.73-0.86) for seven or more times per week (P<0.001 for trend).
• Nut consumption was inversely associated with the risk of most major causes of death, including death due to cancer (any nut, pooled data: HR: 0.91, 95%CI: 0.85-0.97), heart disease (any nut, pooled data: HR: 0.74, 95%CI: 0.68-0.81) and respiratory disease (any nut, pooled data: HR: 0.81, 95%CI: 0.65-1.01).
• Significant inverse associations remained largely unchanged in sensitivity analyses that excluded participants who had ever smoked or who had an extremely high or low BMI, or participants with diabetes, or when correcting for differences in dietary intake.
• Separate analyses for the consumption of peanuts vs tree nuts gave similar associations with total and cause-specific mortality. Nut consumption of two or more times vs. no nut intake gave a multivariate-adjusted HR for death of 0.88 (95%CI: 0.84-0.93) for peanuts and 0.83 (95%CI: 0.79-0.88) for tree nuts.

Conclusion

In two large prospective U.S. cohorts, significant, dose-dependent inverse associations were found between nut consumption and total mortality. Inverse associations were also seen for specific major causes of death including heart disease, cancer and respiratory diseases. Similar results were seen for peanuts and tree nuts. 

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References

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2. González CA, Salas-Salvadó J. The potential of nuts in the prevention of cancer. Br J Nutr 2006;96:Suppl 2:S87-S94. [Erratum,Br J Nutr 2008;99:447-8.]
3. Sabaté J, Oda K, Ros E. Nut consumption and blood lipid levels: a pooled analysis of 25 intervention trials. Arch Intern Med 2010;170:821-7.
4. Estruch R, Ros E, Salas-Salvadó J, et al. Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med 2013;368:1279-90.