Mediterranean diet beneficial in US populations, too

December 17, 2007

Bethesda, MD - The largest study to evaluate the Mediterranean diet and mortality in a US population has found that adherence to such a diet reduces deaths[1]. Dr Panagiota N Mitrou (now of University of Cambridge, UK) and colleagues from the US National Cancer Institute report their findings in the December 10/24, 2007 issue of the Archives of Internal Medicine.

This is the latest in a line of studies to show the benefits of a Mediterranean diet, say the researchers, with all of them having reported reverse associations between this diet pattern and mortality. "Individuals who include more of the Mediterranean diet key components in their diet compared with those who include less have a reduced risk of dying of any cause, including cancer and cardiovascular disease," Mitrou told heart wire .

This is also the first study of mortality that examines the effect of the Mediterranean diet among smokers and those of differing body mass indexes (BMIs), Mitrou said. The researchers found that the diet appears to be particularly beneficial among smokers but that it was not really helpful among obese subjects who had never smoked.

20% reduction in death for those conforming to Mediterranean diet

Mitrou et al followed 214 284 men and 166 012 women in the National Institutes of Health (NIH) AARP (formerly American Association of Retired Persons) Diet and Health Study. During follow-up for all-cause mortality (1995-2005), 27 799 deaths were documented. In the first five years of follow-up, there were 5985 cancer deaths and 3451 CVD deaths.

The researchers modified the traditional Mediterranean 9-point diet score slightly to compose an alternative Mediterranean diet score, thought to better reflect the dietary habits of a US population.

One point each is given for intake at or above the sex-specific median intake for components considered to be healthy—vegetables (excluding potatoes), fruits, nuts, legumes, grains, fish, and monounsaturated-fat/saturated-fat ratio—and one point is given for intake less than the median for those components considered unhealthy (red and processed meat). In addition, one point is given for alcohol intake within a specified range (5-25 g/day).

They looked at conformity with the Mediterranean dietary pattern among participants and calculated hazard ratios (HRs) using age- and multivariate-adjusted Cox models. They found, on average, a 20% reduction in deaths in those conforming highly to the diet (scoring 6 to 9 points) compared with those who had low diet scores (0 to 3 points).

Multivariate adjusted HRs for mortality among men and women scoring 6-9 points on the Mediterranean diet score compared with those scoring 0-3 points

Mortality outcome Men p for trend Women p for trend
All-cause 0.79 <0.001 0.80 <0.001
CVD 0.78 <0.001 0.81 0.01
Cancer 0.83 <0.001 0.88 0.04

Mitrou explained to heartwire that although their primary analysis was based on an alternative Mediterranean diet score, they also ran models using the traditional score and found similar outcomes.

All prior research in this field has shown a benefit of the Mediterranean diet, with reductions in mortality ranging from 8% to 31%, she added.

"These findings confirm results from previous studies and suggest that the Mediterranean dietary score is a useful tool for evaluating diet and mortality in a non-Mediterranean US population," she and her colleagues observe.

And although the alternative Mediterranean diet score they used is not exactly the same as the traditional Mediterranean diet, "it does include the key features of this diet and, as we have shown, may have a substantial beneficial impact on mortality in the United States."

Adhering to Mediterranean diet cuts smokers' death risk by up to 45%

Mitrou et al also found the effects of the diet were even more pronounced in smokers and especially in lean smokers. Among smokers with normal BMI (18.0-25.0), the multivariate HR comparing high vs low levels of adherence to the Mediterranean diet was 0.54 in men and 0.59 in women. This could be due to the diet's antioxidant properties, they suggest.

 
It seems from this finding that conformity with the Mediterranean diet may play a particularly important role among smokers.
 

"It seems from this finding that conformity with the Mediterranean diet may play a particularly important role among smokers, who are characterized by high levels of oxidative stress and an adverse blood lipid profile," says Mitrou.

And they found an inverse association between adherence to the diet and all-cause mortality in most BMI subgroups, with the exception of never-smokers with a BMI of 30.0 or higher (HR 0.92 for men scoring 6 to 9 points compared with those scoring 0 to 3 points; p=0.51 and HR 0.89; p=0.12 for women). They suggest that the increased risk of death due to obesity might mask the inverse association of the Mediterranean diet with all-cause mortality.

Mitrou told heart wire that one previous European study found that risk of death among smokers was lower in those who had the highest adherence to the Mediterranean diet. However, this study did not look at smoking and BMI together, she noted.

As this is the first study to look at the effect of the Mediterranean diet within both smoking and BMI strata, "additional studies are needed to further investigate this finding," she says.

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