Physical Activity Linked to Maintenance of Kidney Function in Older Adults

Laurie Barclay, MD

December 14, 2009

December 14, 2009 — Higher levels of physical activity (PA) are associated with a lower risk for rapid decline in renal function among older adults, according to the results of a cohort study reported in the December 14/28 issue of the Archives of Internal Medicine.

"Habitual...PA has both physiologic and metabolic effects that may moderate the risk of kidney function decline," write Cassianne Robinson-Cohen, MS, from the University of Washington, Seattle, and colleagues. "We tested the hypothesis that higher levels of PA are associated with a lower risk of kidney function decline using longitudinal data from a large cohort of older adults."

The study cohort consisted of 4011 ambulatory participants 65 years or older who were enrolled in the Cardiovascular Health Study (CHS) and who had completed at least 2 measurements of kidney function for 7 years. PA score (ranging from 2 - 8) was calculated by adding kilocalories expended per week (ordinal score of 1 - 5 from quintiles of kilocalories per week) and walking pace (ordinal score for categories of < 2, 2 - 3, and > 3 mph). Glomerular filtration rate (GFR) was estimated using longitudinal measurements of cystatin C levels, with rapid decline in kidney function (RDKF) defined as loss of GFR of more than 3.0 mL/minute/1.73 m2 per year.

RDKF occurred in 958 participants (23.9%; or 4.1 events per 100 person-years). The highest PA group (score of 8) had an estimated risk for RDKF of 16% vs 30% in the lowest PA group (score of 2). Multivariate adjustment revealed that compared with the 2 lowest PA groups (score of 2 - 3), the 2 highest PA groups (scores of 7 - 8) had a 28% lower risk for RDKF (95% confidence interval, 21% - 41% lower risk).

"Greater kilocalories of leisure-time PA and walking pace were also each associated with a lower incidence of RDKF," the study authors write. "Higher levels of PA are associated with a lower risk of RDKF among older adults."

Limitations of this study include observational design, potential for confounding, survivorship bias, and use of participant questionnaires.

"These findings suggest a causal relationship of exercise with a lower risk of kidney disease progression in older people; however, this observational study cannot prove a cause-effect relationship," the study authors conclude. "These findings motivate further studies to evaluate whether exercise represents a viable method for protecting against age-related decline in kidney function."

In an accompanying editorial, Janet E. Fulton, PhD, from the Centers for Disease Control and Prevention in Atlanta, Georgia, and colleagues note that these findings should not be generalized to young or middle-age populations.

"When isolating components of the physical activity prescription, it is important to control for the other components that comprise the total volume of physical activity (the product of frequency, intensity, and time) in the analysis because intensity is directly related to energy expenditure," the editorialists write.

"If time is held constant, an individual expends about twice the energy participating in a vigorous-intensity activity as in a moderate-intensity activity. The optimal physical activity dose for many chronic diseases is not well established, therefore, well-conducted studies that attempt to disentangle components of the physical activity prescription and their independent effects on health will greatly contribute to the evidence base on physical activity and health."

The National Institutes of Health, the National Heart, Lung, and Blood Institute; the National Institute of Neurological Disorders and Stroke; and the National Institutes on Aging supported this study. The study authors and editorialists have disclosed no relevant financial relationships. The opinions of the editorialists do not necessarily represent the official position of the Centers for Disease Control and Prevention or the National Heart, Lung, and Blood Institute.

Arch Intern Med. 2009;169:2116-2123, 2124-2127.

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