Nuts and all-cause mortality

Published - Written by Daniela Lamas

Can a handful of cashews a day make you live longer?

It might sound nutty, but an epidemiological study published in this week’s issue of NEJM suggests that regularly eating nuts is associated with a lower rate of death.

The idea that nuts – a nutrient-dense food, full of unsaturated fatty acids, fiber and vitamins and minerals – can have a beneficial effect on health isn’t new. Researchers have found that people who eat nuts have lower levels of cholesterol, decreased rates of heart disease, diabetes, colon cancer and gallstones.

But are people who eat nuts simply more likely to be health…conscious? A recent randomized study suggested there’s more to it – those assigned to a Mediterranean diet, which included nuts, had a significantly reduced risk of heart attacks than their comparison group who consumed a control diet.

While intriguing, these data left open the question of whether nuts are in fact associated with a lower risk of death from all causes. To tease out the answer to that question, Ying Bao and colleagues turned to two cohort studies that have been gathering data from nurses and healthcare workers for decades.

Within the wealth of accumulated information were detailed dietary questionnaires, filled out every two to four years. Study participants reported whether they ate nuts regularly – at a one ounce, or about 15-20 nuts, serving size – and if so, how frequently. The investigators then separated the participants into groups based on their nut consumption, and looked at how their outcomes compared to those who didn’t eat nuts.

They found that those who ate nuts the most frequently – at least seven times a week – had a 20 percent lower risk of dying than those who didn’t eat nuts at all. When the researchers looked at specific causes of death, the finding held up. Nut eaters were less likely to die from heart disease, cancer or respiratory diseases. The type of nut didn’t seem to matter – peanuts were just as good as tree nuts, a category that includes cashews and almonds.

The investigators then conducted statistical analyses to better assess whether actually eating nuts – rather than some other characteristic of those who tend to snack on nuts – was directly associated with decreased mortality. To that end, they adjusted the results for other known dietary predictors of mortality, like salt and olive oil intake. And the association between nuts and longer life held up.

Of course, an observational study cannot prove cause and effect, and the authors acknowledge as much in their discussion. Frequent nut eaters were leaner than others in the study. And it is also possible that some unmeasured characteristic of the nut-eating group might be responsible for their better health. This study can’t tell us whether adding a handful of nuts to our diets will, ultimately, lead to longer life. But while we await a randomized trial to give us that answer, it surely can’t hurt to try – and it’ll probably taste good, too.

For an animated overview of this study, check out the NEJM Quick Take.

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