The study found that five or more one-ounce servings of walnuts per week was associated with higher life expectancy among older US adults.
Lead investigator Yanping Li, senior research scientist at the Department of Nutrition at Harvard T.H. Chan School of Public Health, received "research support from California Walnut Commission," says the paper, which notes that. "The funder has no role in the design and conduct of the study, in the collection, analysis, and interpretation of the data, and in the preparation, review, or in the decision to publish the results. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose."
"What we've learned from this study is that even a few handfuls of walnuts per week may help promote longevity, especially among those whose diet quality isn't great to begin with. It's a practical tip that can be feasible for a number of people who are looking to improve their health, which is top of mind for many people," said Li.
One ounce of walnuts provides protein (4g), fiber (2g), magnesium (45mg), and essential omega-3 ALA (2.5g).
There has been previous research supporting similar findings, noted the study's researchers, who cited a 2018 study which found that those who followed a Mediterranean diet supplemented with extra virgin olive oil and nuts had 45% lower mortality risk and 47% lower risk for mortality from cardiovascular causes.
Walnuts in varying amounts can have a positive health impact
Study researchers examined data from 67,014 women of the Nurses' Health Study with an average age of 63.6 years and 26,326 men from the Health Professionals Follow-up Study aged 63.3 years in 1986. Participants were relatively healthy when they joined the studies (e.g., free of cancer, heart disease, and stroke) and were followed for about 20 years (1998-2018), noted researchers. Dietary intake was assessed every four years in which participants reported on their overall dietary intake - including how often they consumed walnuts, other tree nuts, and peanuts – as well as lifestyle factors like exercise and smoking status.
Based on this data, the researchers were able to identify associations between walnut consumption at varying levels and different health indicators related to longevity.
According to researchers, eating five or more servings per week was associated with 25% lower risk of dying from cardiovascular diseases, and a gain in about 1.3 years of life expectancy, compared to those who didn't consume walnuts.
Consuming walnuts in lower amounts had its benefits too, said researchers, who found that those who consumed walnuts two to four times per week had a 14% lower risk of dying from cardiovascular diseases, and a gain in about one year of life, compared to non-walnut consumers.
And for those with a 'suboptimal diet,' eating one-half serving of walnuts per week was associated with health benefits including a 26% lower risk of death from cardiovascular diseases, reported researchers.
Limitations of the study
Noting that the research was purely observational, researchers emphasized that the results did not prove a direct cause and effect, but rather supports that walnuts can contribute to an overall healthy lifestyle.
Other factors that contributed to improved life expectancy among those who consumed higher amounts of walnuts were also at play and likely had an impact on findings, noted researchers.
"Participants with a higher frequent consumption of walnuts tend to be more physically active, have a healthier diet, lower alcohol consumption, and take multivitamins," wrote researchers in the study.
The study also relied on participants' self-reported intake of walnuts along with the homogeneity of their participant pool (who were all in the healthcare field), which could have further impacted findings.
However, noted researchers, "Our study has strengths, including the long follow-up of two large cohorts and the repeated measures on detailed diet and lifestyle variables."