Norra MacReady

November 06, 2009

November 6, 2009 (San Diego, California) — High intakes of certain nutrients may have an effect on renal function, Julie Lin, MD, MPH, an internist and nephrologist at Brigham and Women's Hospital in Boston, Massachusetts, said here at Renal Week 2009, the annual meeting of the American Society of Nephrology.

In an analysis of data from the Nurses' Health Study, sodium consumption in the highest quartile was associated with significantly higher odds of renal function decline compared with sodium intake in the lowest quartile. In contrast, beta carotene intake in the highest quartile was associated with a decrease in risk of nearly 40% compared with in the lowest quartile.

"This is another reason not to take a high-salt diet," said Dr. Lin. She presented the findings here during a free communication session.

High-protein diets are thought to hasten progressive renal decline through hyperfiltration, and some data suggest that low-protein diets may protect kidney function. However, data on the effect, if any, of other nutrients on renal function are scarce, Dr. Lin explained. She and her coauthor, Gary Curhan, MD, ScD, examined long-term associations between individual nutrients and kidney function in 3296 women participating in the Nurses' Health Study. The participants were included in the Kidney Function Decline or Type 2 Diabetes Mellitus substudies of the Nurses' Health Study and had had their plasma creatinine and nutrient levels analyzed in 1989 and 2000. Nutrient consumption was estimated from food diaries and frequency questionnaires, which tracked the subjects' consumption of more than 130 foods and beverages during the previous year.

At baseline, median age was 67 years, and median estimated glomerular filtration rate was 76 mL/minute/1.73 m2, which Dr. Lin described as "well-preserved" for women of that age.

Overall, the primary outcome measure — a decrease in estimated glomerular filtration rate of 30% or more — was seen in 372 (11.2%) of the participants during 11 years. This represented a median increase in plasma creatinine of 0.33 mg/dL. After multivariate adjustment, the highest quartile of sodium intake was associated with an odds ratio of 1.52 for the primary outcome compared with the lowest quartile. For beta carotene, the odds ratio was 0.62 for the highest vs the lowest quartile of intake.

No other significant associations were seen for the other nutrients analyzed, such as animal fat, low-fat dairy products, vitamin E, folate, other vitamins, protein, and monounsaturated fat, said Dr. Lin.

This study included mostly older white women, and it is possible that men, younger people, or people of different ethnicities might have different results, although "there's no biological reason why these findings would not apply to them, too," she noted.

Overall, these findings suggest that "dietary modification may represent an important strategy for maintaining kidney health," Dr. Lin concluded.

"The finding of a strong association between kidney function and the highest level of nutrient intake is very interesting," said Talat Ikizler, MD, associate professor of medicine at Vanderbilt University, Nashville, Tennessee, and director of the university's outpatient dialysis clinic. Dr. Ikizler, who was not involved in this research, cautioned that this was an associative study and cannot show cause and effect. Still, he said, "it suggests that we must pay more attention to the nutritional needs of our patients."

Dr. Lin and Dr. Ikizler have disclosed no relevant financial relationships.

Renal Week 2009: American Society of Nephrology (ASN) 2009 Annual Meeting: Abstract SA-FC342. Presented October 31, 2009.

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