Mediterranean Diet Linked to Up to 23% Lower Mortality Risk in U.S. Women Over 25 Years

A group of women, all healthy when they signed up, were followed for as long as 25 years. Researchers at Brigham and Women's Hospital, a founding member of the Mass General Brigham system, have now reported what the eating habits of that group showed. More than 25,000 U.S. women took part, drawn from the Women's Health Study. Those whose diets adhered most closely to a Mediterranean pattern had up to 23% lower risk of dying from any cause over the follow-up period. The results are published in JAMA.

The health benefits of the Mediterranean diet have been reported in many studies before. What was thin, according to the researchers, was long-term data on U.S. women, and an understanding of why the diet might lower the risk of death. This study set out to address both.

The diet itself is built around plants: nuts, seeds, fruits, vegetables, whole grains and legumes. Its main fat is olive oil, usually extra virgin. Fish, poultry, dairy, eggs and alcohol are eaten in moderation, while meat, sweets and processed foods are eaten rarely.

The lower risk showed up for both cancer mortality and cardiovascular mortality. Samia Mora, MD, the senior author, is a cardiologist and director of the Center for Lipid Metabolomics at the Brigham. She noted that these are the top causes of death in women and men in the U.S. and worldwide. Her summary for women who want to live longer was to watch their diet, and she said a Mediterranean pattern could mean about a quarter reduction in risk of death over more than 25 years.

To probe the why, the team evaluated a panel of roughly 40 biomarkers representing different biological pathways and clinical risk factors. They found changes in markers of metabolism, inflammation and insulin resistance, among others. Metabolism and inflammation contributed the most. Next came triglyceride-rich lipoproteins, adiposity and insulin resistance. Pathways involving branched-chain amino acids, HDL and LDL cholesterol, glycemic measures and hypertension made smaller contributions.

Lead author Shafqat Ahmad, PhD, is an associate professor of epidemiology at Uppsala University in Sweden and a researcher at the Brigham. He said even modest changes in established risk factors for metabolic disease, particularly those tied to small-molecule metabolites, inflammation, triglyceride-rich lipoproteins, obesity and insulin resistance, can add up to substantial long-term benefit. He said this points to the potential of encouraging healthier eating habits to reduce overall mortality.

The authors are explicit about limits. The participants were middle-aged and older, well-educated female health professionals, predominantly non-Hispanic and white. Diet was measured with food-frequency questionnaires, and height, weight and blood pressure were self-reported. The strengths they cite are the study's large size and long follow-up. They also point out that as the Mediterranean diet has become popular, it has been adapted differently in different countries and cultures.

That last point shapes Mora's policy view. She said medical professionals already recognize the diet's benefits and that this study offers insight into why it works. In her view, public health policy should promote its healthful attributes and discourage unhealthy adaptations. What to watch is whether similar results hold in more diverse groups, and whether policy follows.