A Harvard study that spanned decades of observation has found that people who frequently consume nuts have a 20% lower death rate overall, with various reductions in mortality rates for different causes.

The research, published last month in the New England Journal of Medicine, involved two large groups in the United States, including a group of more than 120,000 female nurses who filled in their first questionnaires in 1980, and 51,529 male health professionals who gave their first responses in 1986.

The results are based on 30 years of follow-up, with the one fifth reduction in mortality rate applying to participants who ate nuts seven or more times per week.

"Age-adjusted and multivariate-adjusted analyses showed a significant inverse association between frequency of nut consumption and total mortality among both women and men," the study authors said.

"Inverse associations were observed for most major causes of death, including heart disease, cancer, and respiratory diseases.

"Results were similar for peanuts and tree nuts, and the inverse association persisted across all subgroups."

The results were presented using hazard ratios, whereby a figure of one would mean no association from nut consumption, and anything above one would mean nut consumption was linked to a higher incidence of the cause of death.

Two of the lowest hazard ratios were for heart disease and kidney disease at 0.74 and 0.69 respectively, while good results were seen for incidences of cancer (0.91), respiratory disease (0.81), infection (0.79), diabetes (0.80) and stroke (0.92) from nut eaters.

"In the pooled analysis of women and men, significant inverse associations were observed for deaths due to cancer, heart disease, and respiratory disease," the authors said.

In a paper discussion, the authors said the effect of confounding by unknown factors could not be ruled out, however the analysis did include a large number of confounding factors that were updated regularly.

"Given the observational nature of our study, it is not possible to conclude that the observed inverse association between nut consumption and mortality reflects cause and effect.

"However, our data are consistent with a wealth of existing observational and clinical-trial data in supporting the health benefits of nut consumption for many chronic diseases."

The authors mentioned several nutrients found in nuts that could be the reason behind the relationship if it is causal, such as unsaturated fatty acids, high-quality protein, fiber, vitamins, minerals and phytochemicals, which may bring cardioprotective, anticarcinogenic, antiinflammatory, and antioxidant properties.

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