The largest study of its kind, published in the New England Journal of Medicine, finds that people who eat a handful of nuts every day live longer than those who do not eat them at all.
Scientists from Dana-Farber Cancer Institute, Brigham and Women's Hospital, and the Harvard School of Public Health came to this conclusion after analyzing data on nearly 120,000 people collected over 30 years.
The analysis also showed that regular nut eaters tended to be slimmer than those who ate no nuts, putting to rest the notion that eating nuts leads to weight gain.
Senior author Charles S. Fuchs, director of the Gastrointestinal Cancer Treatment Center at Dana-Farber and professor of medicine at Harvard Medical School, and colleagues also examined how eating nuts or not related to causes of death.
Prof. Fuchs says:
"The most obvious benefit was a reduction of 29 percent in deaths from heart disease - the major killer of people in America. But we also saw a significant reduction - 11% - in the risk of dying from cancer."
Peanuts and tree nuts showed similar effect
The team also found that the reduced risk of death was similar for both nuts that grow on trees, such as cashews and Brazils, and peanuts, which grow under the ground. Other types of tree nut include almonds, hazelnuts, macadamias, pecans, pine nuts, pistachios and walnuts.
Researchers have found that eating a handful of nuts a day could result in a longer lifespan, and may even reduce the risk of death from heart disease and cancer.
However, the data did not allow them to see whether this was also true for links to protection against certain causes of death.
And while some small studies have linked higher nut consumption to lower death from all causes in certain populations, none has examined the effect in a large population in such detail over a long time.
The more nuts people ate, the less likely they were to die
In this new study, the researchers examined data on 76,464 women between 1980 and 2010 who took part in the Nurses' Health Study, and on 42,498 men from 1986 to 2010 who took part in the Health Professionals' Follow-up Study.
Participants in both cohorts filled in detailed food questionnaires every 2-4 years, and also answered questions about lifestyle and health.
The food questionnaires asked the participants to estimate how often they ate nuts in a serving size of one ounce (about 28g), which is roughly the amount contained in a small packet of peanuts from a vending machine.
The researchers used sophisticated statistical tools to take out the effect of factors that might also have beneficially influenced the risk of death.
For example, they found people who ate more nuts tended to be leaner, to eat more fruits and vegetables, not smoke, be more physically active, and drink more alcohol.
But they were also able to take out the effects of these factors and find an independent link between nut consumption and lower risk of death.
First author Dr. Ying Bao, of Brigham and Women's Hospital, explains what they found:
"In all these analyses, the more nuts people ate, the less likely they were to die over the 30-year follow-up period."
Eating nuts less than once a week was linked to a 7% reduction in risk of death, once a week was linked to an 11% reduction, two to four times a week to a 13% reduction, five to six times a week to a 15% reduction, and seven or more times a week, to a 20% reduction.
The researchers point out that the study was not designed to examine cause and effect and so cannot conclude that eating more nuts causes people to live longer.
However, they say the results are strongly consistent with "a wealth of existing observational and clinical trial data to support health benefits of nut consumption on many chronic diseases."
Grants from the National Institutes of Health and the International Tree Nut Council Nutrition Research & Education Foundation helped finance the study.
In a large prospective study published recently in the British Journal of Cancer, researchers found eating nuts was linked to reduced risk of pancreatic cancer.