Dairy Consumption Reduces Risk of Kidney Disease

Written by: Lauren Milligan Newmark, Ph.D. | Issue # 65 | 2017

Dairy foods are best known for promoting a healthy skeleton, but bones are not the only tissue to reap their health benefits. The very same dairy ingredients—calcium, magnesium, phosphorus, potassium, and protein—that build and maintain a healthy skeleton have demonstrated protective effects on cardiovascular disease, type 2 diabetes (T2D), and hypertension [1]. And now a growing body of evidence [1-6] suggests habitual dairy consumption may benefit the kidneys as well.

Chronic kidney disease (CKD) currently affects 27 million adults in the U.S. [7] and nearly 10% of adults worldwide [8]. CKD is diagnosed based on a filtration rate—the glomerular filtration rate (GFR) to be exact—because the kidneys’ job is to filter the blood. Normal physiological functions, such as protein digestion and muscle activity, create waste products (e.g., urea, creatinine) that need to be removed from the blood and passed into urine. The GFR measures how much of this waste the body filters in a given amount of time. A normal GFR is between 90 and 120 milliliters of blood per minute [1, 7]. Although there is variation in what is considered normal with respect to age, sex, ethnicity, and body size, values below 90 ml/min are considered indicative of abnormal kidney function [7]. CKD is diagnosed when a patient has a GFR less than 60 ml/min for three or more months [1, 5, 7, 8].

The link between dairy foods and bone health is apparent; milk, cheese, and yogurt supply the very minerals needed to construct the skeleton. But how do the ingredients in dairy foods influence the kidneys’ ability to filter out waste?

One potential pathway is indirect; that is, dairy components influence other physiological functions that directly affect renal function [1,2]. Currently, hypertension and T2D are the leading causes of CKD. Elevated blood pressure damages the blood vessels and the nephrons in the kidneys, weakening them and their ability to filter out waste products. Elevated blood sugar levels have a similar effect; by forcing the kidneys to work harder, T2D weakens the kidneys to the point where they pass nutrients the body needs (such as the protein albumin) into urine along with waste products [7]. Indeed, increased albumin in urine, a condition referred to as albuminuria, is itself diagnostic of CKD.

Consumption of dairy foods has been linked to a reduced risk for both hypertension and T2D [9-13]. By keeping blood pressure and blood sugar in check, it stands to reason that dairy also may modify the risk for developing CKD. Indeed, diets designed to lower blood pressure have also demonstrated a protective effect for CKD [3-5]. The DASH diet (Dietary Approaches to Stop Hypertension) focuses on eight food components: high intakes of fruit, vegetables, nuts, legumes, and low-fat dairy combined with low intakes of sodium, sweetened beverages, and red/processed meats [3]. The health benefits conferred by this diet on both blood pressure and cardiovascular disease are attributed to the additive effects of the food components. That is, it is not simply one food ingredient that improves vascular health but the synergistic actions of all ingredients [3]. Viewed this way, dairy foods are part of a larger dietary strategy to improve health including kidney disease but are not themselves the focus of the studies. Nevertheless, a 23-year study of nearly 15,000 middle-aged American men and women [3] identified a lower risk for kidney disease in participants with a higher dairy product intake. Legume and nut intake also demonstrated a protective effect against CKD, whereas consumption of red/processed meat increased CKD risk [3]. These results were echoed in a six-year study on 1600 Middle Eastern adults [4]. Study participants that did better at sticking to the DASH diet, including higher consumption of dairy foods, had lower odds for developing CKD. In both DASH diet studies [3,4], lower CKD risk was not only attributed to what the participants were eating more of but also what they were eating less of (i.e., sodium, red meat, and sugary drinks). Thus, it is not possible to say whether low-fat dairy foods would have had a protective effect (or as significant of an effect) in the absence of the other components of the DASH diet.

It also is possible that dairy foods directly influence the health of the kidneys through their anti-inflammatory and antioxidant properties [1]. Oxidative stress and inflammation are risk factors for CKD and for numerous other chronic diseases, including cancer, T2D, hypertension, and cardiovascular disease. Calcium, magnesium, vitamins A and E, dairy proteins, and even dairy fats have demonstrated antioxidant and anti-inflammatory properties. Thus, it could be multiple dairy ingredients, or the effect of their synergistic actions, influencing kidney function.

Support for a direct effect of dairy on the kidneys comes from a 2016 study [2] on nearly 4000 Dutch adults (aged 25–65) with normal or mildly decreased GFR. The metric of interest was changed in GFR over an extended period of time, and each subject had three or more examinations at five-year intervals from 1993 to 2012. The study authors found that a higher consumption (defined as ≥ 2 serving per day) of milk and low-fat dairy products was associated with a smaller decline in GFR per year. Because the study authors controlled for hypertension and T2D in their statistical analyses, the observed protective effect of dairy consumption, albeit minor (0.11 ml/min per year less decline), was attributed directly to the actions of dairy components, such as calcium, magnesium, and unsaturated fats [2].

One drawback of this study was that it did not look at the influence of dairy foods on kidney function in individuals diagnosed with CKD, making it difficult to say whether the actions of dairy ingredients influence kidney function in all individuals or only those with normal or slightly impaired kidney function. This issue was addressed, however, in a study [1] published just one month after the Dutch study [2]. Gopinath and colleagues [1] report on the association between dairy food consumption, calcium intake, and CKD over a ten-year study period in 1185 Australian adults living in the same area just west of Sydney. Baseline GFR values were not used for inclusion in the study, and thus these values varied across participants from within the normal range to diagnostic of CKD. Like the Dutch study [2], Gopinath et al. [1] found that consuming ≥ 2 servings of low-fat dairy foods per day was associated with a reduced prevalence and incidence of CKD during the study period, independent of hypertension and T2D. This study also compared calcium intake to CKD prevalence and found that individuals who had more calcium in their diet were less likely to have CKD over the study period [1]. Thus, the observed protective effect of low-fat dairy foods is at least partly due to the anti-inflammatory and antioxidant properties of calcium. In the same study population, poor calcium intake was associated with abnormal blood vessels in the retina, and the authors hypothesize that a similar physiological response may be taking place in the kidneys, wherein calcium influences renal blood vessel health [1]. Importantly, dairy (and calcium) intakes were below the recommended daily intake values for 83% of the participants [1], suggesting that even moderate calcium consumption can influence kidney function.

As observational studies, neither the Dutch [2] nor the Australian [1] study was able to establish a cause-and-effect relationship between dairy components and kidney health. But when these studies are combined with numerous others that indicate a protective effect of dairy food consumption on the development of chronic diseases [9-13], it provides a strong framework for developing more rigorous controlled studies. With the rapid increase in the incidence of CKD and other chronic diseases, it is encouraging that easy-to-implement lifestyle changes, such as eating two or more servings of low-fat dairy foods per day, could have such profound health benefits.

References

1. Gopinath B., Harris D.C., Flood V.M., Burlutsky G., Mitchell P. 2016. Associations between dairy food consumption and chronic kidney disease in older adults. Scientific Reports 6, 39532. doi:10.1038/srep39532
2. Herber-Gast G.C.M., Biesbroek S., Verschuren W.M.M., Stehouwer C.D.A., Gansevoort R.T., Bakker S.J.L., Spijkerman A.M.W. 2016. Association of dietary protein and dairy intakes and change in renal function: results from the population-based longitudinal Doetinchem cohort study. American Journal of Clinical Nutrition 104: 1712-1719.
3. Rebholz C.M., Crews D.C., Grams M.E., Steffan L.M., Levey A.S., Miller E.R. III, Appel L.J., Coresh J. 2016. DASH (Dietary Approaches to Stop Hypertension) diet and risk of subsequent kidney disease. American Journal of Kidney Disease 68: 853-861.
4. Asghari G., Yuzbashian E., Mirmiran P., Azizi F. 2017. The association between Dietary Approaches to Stop Hypertension and incidence of chronic kidney disease in adults: the Tehran Lipid and Glucose Study. Nephrology, Dialysis, Transplantation 32: ii224-ii230.
5. Asghari G., Farhadnejad H., Miriran P., Dizavi A., Yuzbashian E., Azizi F. 2016. Adherence to the Mediterranean diet is associated with reduced risk of chronic kidney diseases among Tehranian adults. Hypertension Research. doi:10.1038/hr.2016.98
6. Haring B., Selvin E., Liang M., Coresh J., Grams M.E., Petruski-Ivleva N., Steffen L.M., Rebholz C.M. 2016. Dietary protein sources and risk for incident chronic kidney disease: results from the Atherosclerosis Risk in Communities (ARIC) Study. Journal of Renal Nutrition 4 (2017): 233-42.
7. Baumgarten M., Gehr T. 2011. Chronic kidney disease: detection and evaluation. American Family Physician 84: 1138-1148.
8. National Kidney Foundation: https://www.kidney.org/kidneydisease/global-facts-about-kidney-disease
9. Wang L., Manson J.E., Buring J.E., Lee I-M., Sesso H.D. 2008. Dietary intake of dairy products, calcium, and vitamin D and the risk of hypertension in middle-aged and older women. Hypertension 51: 1073-1079.
10. Ralston R.A., Lee J.H., Truby H., Palermo C.E., Waler K.Z. 2012. A systematic review and meta-analysis of elevated blood pressure and consumption of dairy foods. Journal of Human Hypertension 26: 3-13
11. Comerford K.B., Pasin G. 2016. Emerging evidence for the importance of dietary protein source on glucoregulatory markers and type 2 diabetes: Different effects of dairy, meat, fish, egg, and plant protein foods. Nutrients 8: 446; doi:10.3390/nu8080446
12. Ballard K.D., Bruno R.S. 2015. Protective role of dairy and its constituents on vascular function independent of blood pressure–lowering activities. Nutrition Review 73: 36-50.
13. Aune D., Norat T., Romundstad P., Vatten L.J. 2013. Dairy products and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis of cohort studies. The American Journal of Clinical Nutrition, ajcn-059030.

Back to SPLASH!^® Home