Mediterranean Diet Linked to Lower Mortality in Older Men with Chronic Kidney Disease

For people with chronic kidney disease (CKD) who followed a Mediterranean-style diet, renal function improved. The more these people adhered to such a diet, the more improvement was seen in survival, according to the results of a study presented at the 50th Congress of the European Renal Association—European Dialysis and Transplant Association in Istanbul, Turkey, in May.

The Mediterranean diet consists largely of plant-based foods such as fruits and vegetables, whole grains, legumes, and nuts; healthful oils such as olive and canola; and some fish and poultry but limits red meat and saturated fats. Red wine in moderation is optional; it has been associated in various populations with lower risks of illness and mortality. However, few data exist regarding kidney function in community-dwelling adults who follow such a diet.

Juan Carrero, PhD, of the Karolinska Institute in Stockholm and co-workers conducted an observational study on a population-based cohort (the Uppsala Longitudinal Study of Adult Men) of 1110 Swedish men around 70 years old to see whether the men who followed a Mediterranean diet had improved kidney function, lower cardiometabolic risks, and reduced mortality. From 7-day diet diaries that the men recorded, the researchers determined their dietary habits, from which they calculated a Mediterranean Diet Score, allowing classification of the participants as low, medium, or high adherents to such a diet.

Within the cohort, 506 men had GFRs of less than 60 mL/min per 1.73 m2 and were therefore considered to have CKD. Deaths were recorded during a median follow-up time of 9.9 years.

During follow-up, 168 of the 506 individuals with CKD died. Better adherence to the diet was independently associated with better survival. For every two-point increase in the Mediterranean Diet Score, the investigators observed an 18 percent lower risk of death, with a stronger association in those individuals who had adequate dietary intakes.

Of the individuals who died, the adherence groups did not differ in their cardiometabolic risk factors. “Most potential explanatory risk factors for the mortality association, such as obesity, blood pressure, lipoproteins, glucose, insulin, or inflammation, did not associate with a greater or poorer adherence to the diet,” Carrero said. To some extent, this lack of association with such risk factors may be attributable to the homogeneous nature of the cohort: men of about the same age, from the same region, and of the same ethnicity. “In addition…the benefits of the Mediterranean diet may be mainly accounted for by individual nutrients, such as high fiber intake and high PUFA [polyunsaturated fatty acids] but low SFA [saturated fatty acid] intake rather than by the score as a whole,” he said.

In comparison with low adherents to the diet, high adherents had a 42 percent lower risk of CKD after adjustment for body mass index, physical activity, smoking, education, hypertension, hyperlipidemia, and diabetes (adjusted odds ratio 0.58; 95 percent confidence interval 0.38–0.87; p for trend = 0.04).

Carrero pointed out that adherence to a Mediterranean diet is not very common among older individuals in Scandinavia, so the adherence scores were relative within that population. “Thus, a high adherence to this diet means that among the individuals studied, they had an intake of food most in accordance with the Mediterranean style,” he explained. A potential confounding factor in the study is that individuals with low adherence to a Mediterranean diet may also have been less compliant with other lifestyle and medical advice.

The strengths of the study are its prospective nature; the use of the 7-day dietary record, which is the preferred method for dietary assessment; and the use of a national mortality registry with 100 percent inclusion. The limitations include a lack of data on the use of dietary supplements and the fact that about half of the participants did not provide adequate dietary recall results. Finally, because the study involved elderly men with moderate CKD from a rather homogeneous population, the results may not be applicable to other populations.

Because of the observational nature of the study, one cannot draw a causal link between adherence to a Mediterranean diet and improved kidney function or lower mortality. The investigators therefore suggest initiating interventional studies to formally test such a link.

July 2013 (Vol. 5, Number 7)