Reference
Luu HN, Blot WJ, Xiang YB, et al. Prospective evaluation of the association of nut/peanut consumption with total and cause-specific mortality. JAMA Intern Med. 2015 Mar 2. [Epub ahead of print]
Design
This study examined the association of nut consumption with total and cause-specific mortality in Americans of African and European descent who were predominantly of low socioeconomic status (SES) and in Chinese individuals living in Shanghai, China.
Participants
Participants came from 3 separate, large cohorts. The first cohort was comprised of 71,764 US residents of African or European descent, primarily of low SES. These participants were part of the Southern Community Cohort Study (SCCS) conducted in the southeastern United States between March 2002 and September 2009. Another 134,265 participants were drawn from 2 cohorts in Shanghai China: the Shanghai Women’s Health Study (SWHS; December 1996-May 2000) and the Shanghai Men’s Health Study (SMHS; January 2002-September 2006).
Study Medication and Dosage
Food frequency questionnaires were used to assess overall nut and peanut consumption. In the Shanghai cohorts, tree nut consumption was rare and the majority of nuts consumed were peanuts. In the US cohort, about half the nuts consumed were peanuts.
Outcome Measures
Deaths in the US cohort were ascertained through the National Death Index and Social Security Administration mortality files; in China, deaths were confirmed via the Shanghai Vital Statistics Registry and through biennial home visits in the SWHS and SMHS studies.
Key Findings
During a median follow-up of 5.4 years in the SCCS, 6.5 years in the SMHS, and 12.2 years in the SWHS, 14,440 deaths were identified. Nut intake was inversely associated with risk of total mortality in all 3 cohorts (all P<0.001), with adjusted hazard ratios (HRs) associated with the highest vs lowest quintiles of intake being 0.79 (95% confidence interval [CI]: 0.73-0.86) and 0.83 (95% CI: 0.77-0.88), respectively, for the US and Shanghai cohorts. This inverse association was driven by a reduction in cardiovascular deaths (P<0.05 in the US cohort; P<0.001 in the Shanghai cohorts). In comparing highest vs lowest quintiles of nut consumption, when specific types of cardiovascular disease were examined, a significant inverse association was consistently seen for ischemic heart disease in all ethnic groups (HR: 0.62, 95% CI: 0.45-0.85 in blacks; HR: 0.60, 95% CI: 0.39-0.92 in whites; and HR: 0.70, 95% CI: 0.54-0.89 in Asians). The associations for ischemic stroke (HR: 0.77, 95% CI: 0.60-1.00) and hemorrhagic stroke (HR: 0.77, 95% CI: 0.60-0.99) were significant only in Asians. The nut-mortality association was not modified by the presence of metabolic conditions at study enrollment and was similar for men and women and for blacks, whites, and Asians. The benefit of eating nuts seems to apply across racial and economic lines. The benefits of peanut consumption did not differ from tree nut consumption.
Practice Implications
This study tells us 2 important things.
First, eating nuts certainly appears beneficial, as it is associated with lower overall mortality and in particular with a 30% to 40% decrease in mortality from ischemic heart disease across racial and class lines. While we might have assumed this already based on earlier studies, the present study may be the first to actually confirm it.
Second—and perhaps more important—consuming peanuts, which are technically not even nuts, appears to provide the same health benefits as does eating true tree nuts.
Peanuts are inexpensive and will probably remain so. They are a global crop, grown in multiple countries and available as a locally grown and sold commodity in many countries.
This is far from the first large study suggesting that eating nuts is beneficial. A 2014 meta-analysis by Luo et al of 11 studies found that nut consumption was inversely associated with total mortality, though it did not provide information on cause-specific mortality.1 Bao et al in a 2013 report that analyzed data from the US Nurses’ Health Study and the Health Professionals Follow-up Study also found that nut consumption was inversely associated with all-cause, cancer-specific, and heart disease mortality.2 Data from the Prevención con Dieta Mediterránea or PREDIMED trial cohort reported that baseline nut consumption was associated with reduced mortality in people following a Mediterranean-style diet.3
In the latest meta-analysis on nut consumption and all-cause mortality by Grosso et al, the combined studies included 354,933 participants, 44,636 cumulative incident deaths, and 3,746,534 cumulative person-years. They found just 1 serving of nuts per week resulted in a 4% decreased risk for all-cause mortality. One serving per day was associated with a 27% decreased risk of cardiovascular disease mortality.4
Participants in the earlier trial cohorts have been predominately educated Caucasian professionals. Questions have arisen whether the same benefits from eating nuts would be seen in other races and in people of lower economic status. This current paper tells us that the answer is a clear affirmative.
This paper also tells us demonstrably that when it comes to cardiovascular disease, we should expect peanuts to have the same impact as tree nuts. As noted, peanuts are not nuts at all but rather belong to the legume family; they are peas. Their Latin name is Arachis hypogaea. Arachis is a genus that includes about 70 species of flowering pea plants. Hypogaea means below (hypo) the earth (Gaea). After the plants produce typical-looking pea flowers, the flower stalks do something unusual; they elongate, bend over, and push their flower ovaries into the ground where the legume pods mature. Archaeologists have found evidence of peanut cultivation in Peru from some 3500 to 4500 years ago,5 but peanuts probably originated even earlier somewhere between southern Bolivia and northern Argentina.6 Since peanuts are actually peculiar peas that ripen underground, it’s curious that we group them together with nuts.
The information in this study is important for a purely practical and economic reason. Tree nuts like almonds are expensive and likely to become more so. California produces 82% of the world’s annual crop,7 so not only are the almonds eaten in the US grown there, but so are the majority of the almonds eaten worldwide. Growing almonds requires a great deal of water. Approximately 10% of California’s water supply goes to growing almonds.8 Yet in April 2015, California reported the lowest snowpack in the state’s history, just 7% of the 75-year average.9 This melting snowpack would normally supply the water used to irrigate almond groves.
As California’s current drought shows no sign of letting up and most almonds come from California, the price of almonds, and, in turn, other tree nuts, will likely go up. At the same time, almond consumption is increasing; US per capita consumption went up from 1.3 lbs to 1.8 lbs a year between 2008 and 2012.7
Peanuts are inexpensive and will probably remain so. They are a global crop, grown in multiple countries and available as a locally grown and sold commodity in many countries. China leads the world in peanut production but still is only responsible for 42% of the crop.10 For many people, in particular those with limited income, peanuts could be the nut of choice.
A small but fascinating detail in this paper is how few nuts were needed to effect a change in mortality risk. The upper quintile of nut and peanut consumption was equal to or greater than 2.54 g per day or about 20 g per week, and the average “handful of peanuts” weighs almost twice that amount.11
[Editors' note: To learn about treating peanut allergy, read “Is the Solution to Peanut Allergy Early Exposure to Peanuts?” in this issue of Natural Medicine Journal.]
