The Effects of Hypertension on Kidney Function and Chronic Kidney Disease Risk

Abstract

Hypertension (HTN) is the second leading cause of chronic kidney disease (CKD) in the United States after diabetes (Marieb & Hoehn, 2016). Although HTN is a modifiable risk factor for CKD, the severe health consequences of uncontrolled high blood pressure (BP) are often overlooked by patients and physicians alike. The purpose of this literature review is to compare recent research studies to determine how HTN affects kidney function and whether or not it increases the risk of CKD. This paper analyzes eight original research studies published within the last fifteen years that sought to establish an association between high BP and kidney function. The studies reveal that HTN causes CKD and that reductions in BP can prevent the disease. However, hypertensive patients’ perceived risk and adherence to BP management does not always reflect the health implications of these findings. This problem may be amplified in developing countries where healthcare is less consistent and patients are less likely to seek professional medical advice. The screening and treatment of apparently asymptomatic individuals may be extremely important for preventing CKD worldwide. Complementary and alternative medicine (CAM) treatments for HTN include the Dietary Approach to Stop Hypertension (DASH) diet, herbal remedies, regular exercise, weight loss, limitation of alcohol intake, and various stress management programs.

Introduction

Hypertension (HTN) and chronic kidney disease (CKD) are major public health concerns worldwide. About one in three U.S. adults has high blood pressure (BP), and one in six Americans live with CKD. Despite this high incidence, only one-third of U.S. patients are actually treated to lower BP to an acceptable level (Eskridge, 2010). Prolonged HTN is a major cause of heart failure, vascular disease, kidney failure, and stroke. It is also the second leading cause of CKD in the United States after diabetes (Marieb & Hoehn, 2016). 

HTN negatively affects the kidneys by damaging blood vessels and reducing their ability to work properly. Blood vessels stretch when BP is high, causing scarred and weakened blood vessels in the kidneys. This in turn reduces the kidneys’ ability to remove wastes and extra fluids in the body, raising BP even higher (High Blood Pressure, 2014). As kidneys lose the ability to remove wastes from the body, nitrogenous wastes accumulate in the blood and blood pH levels become more acidic. CKD can also cause complications such as anemia, weak bones, and nerve damage, and may increase the risk of heart disease (About CKD, 2017). 

While HTN is a modifiable risk factor for CKD, high BP frequently goes unnoticed because it has few symptoms. Reasons for the mismanagement of HTN vary, but may include ineffective patient teaching, poor lifestyle modifications, and/or limited access to healthcare (Eskridge, 2010). The purpose of this literature review is to compare recent research studies to determine how HTN affects kidney function and whether or not it increases the risk of CKD. 

Methods

For this literature review, the researcher used the search parameters “high blood pressure” AND “kidney disease” in either the title or abstract of the article in ProQuest Central and PubMed. The search was limited to free full text and peer reviewed original research studies published within the last fifteen years that sought to establish an association between high BP and kidney function. This review includes the eight original research studies found within these parameters. The purpose of this review is to compare the most recent articles available in scientific literature to determine how HTN affects kidney function and whether or not it increases the risk of CKD. 

Results

The ARIC (Atherosclerosis Risk in Communities) study is a population-based study of cardiovascular disease and its risk factors. Hardy et al. (2018) followed 15,390 Americans between the ages of 45 and 64 years from the ARIC study to analyze the predicted effects of BP reductions on the general population. The researchers state that CKD affects an estimated 14.8% of US adults and HTN is a major modifiable risk factor for CKD. Over a mean of 20 years of follow-up, 3,852 CKD events were reported. A reduction in systolic BP across the population was associated with approximately 11.7 and 13.4 fewer CKD events per 100,000 in blacks and whites, respectively. The researchers conclude that modest reductions in systolic BP across a population offer an effective method to prevent a large number of CKD events. This could be an important component of CKD prevention. 

Similarly, in a study by Okin, Kjeldsen, and Devereux (2016), 8,778 hypertensive patients were followed to determine the association between high BP and reduced renal function. The researchers found that treatment of HTN may be associated with a slower reduction of renal function over a 4-year follow-up period. Their findings suggest that treating HTN to lower systolic BP goals may be a means to slow the progression of HTN related renal dysfunction.

In a prospective cohort study of 1,703 white-collar workers in China, Cao, Xie, Zhou, Yuan, and Chen (2014) investigated whether prehypertension (PHTN) was associated with the progression of CKD. The participants did not have CKD in 2006 at baseline and were followed for an average of 54 months by annual examinations. During the follow-up, 194 incidences of CKD were recorded. The risk for CKD in PHTN was found to be significantly higher compared to individuals with normal BP. The study found that 2.4 % of CKD incidence may be derived from PHTN. Although current guidelines recommend CKD screening only among those with HTN, screening among those with PHTN could significantly help prevent the disease. 

Vanelli et al. (2018) conducted a population-based, cross-sectional study of 1,016 participants in Brazil with a mean age of 44. Using a questionnaire to determine individual risk of CKD, the researchers attempted to track CKD and its causes. It is estimated that in Brazil more than two million individuals have some degree of renal dysfunction and 100,000 of them are in renal replacement therapy. In this relatively young population (58.5% of participants were younger than 50 years), the study detected a high risk for CKD, which stresses the importance of early detection even in asymptomatic individuals. The researchers also found a high prevalence of diabetes mellitus (10.5%) and high BP (34.7%) in the population, which are recognized as the main causes of CKD. The study found an increased risk for CKD in approximately 31% of this relatively young and asymptomatic group. They conclude that a simple and easily implemented screening method, similar to the questionnaire used in this study, could be of great value in the prevention and surveillance of CKD in Brazil. 

In a longitudinal study of 23,894 Japanese adults, Nishikawa et al. (2015) analyzed the impact of metabolic factors on CKD in non-obese individuals. Metabolic factors were defined as obesity, high BP, high triglycerides, low high-density lipoprotein cholesterol, and high fasting blood sugar. CKD was defined as having renal dysfunction (GFR <60 mL/min/1.73 m2 ) or proteinuria. Of the 2,867 subjects with three or more metabolic factors, 650 (22.7%) were non-obese. Of the entire 23,894 subjects, 1,764 developed renal dysfunction and 904 developed proteinuria over an average of 7.8 years of follow-up. The study found an overall increased risk of both renal dysfunction and proteinuria in subjects with metabolic factor clustering, regardless of obesity. The incidence of renal dysfunction was slightly higher among non-obese participants with 3 or more metabolic factors. These findings are important because non-obese individuals are often considered to be at a lower risk of CKD and thus managed as such. It remains unclear whether metabolic syndrome is in itself a risk factor for CKD or if individual factors, such as HTN and diabetes, are more important. 

In a retrospective cohort study, Ladi-Akinyemi and Ajayi (2017) aimed to determine CKD risk factors at a hospital in Ogun-State, South West Nigeria. The study included a case cohort of 150 patients (GFR <60 mL/min/1.73 m2 or evidence of kidney damage for more than three months) and a control cohort of 300 (patients at the orthopedic unit of the surgery department). The mean age of cases and controls was 40.6 and 38.6 years, respectively. The researchers stated that the incidence of CKD is higher in developing countries and kidney disease accounts for approximately 6-12% of medical admissions in Nigeria. HTN is the leading cause of kidney failure in Nigeria. This study found that CKD most frequently occurred in men in the early to middle age group, who were either diabetic or hypertensive. Compared to the control group, a larger percentage of the cases had a family history of CKD, high BP, diabetes, HIV positive, urinary tract infection, and history of cancer. CKD patients also reported more regular use of NSAIDs and more frequent addition of salt to cooked foods. Most of the cases had elevated systolic and diastolic BP at presentation, yet more than half of these cases were not known hypertensive. This could suggest a level of ignorance on the part of both Nigerian government and citizens. Nigerians do not participate in routine medical check-ups and poor health planning and facilities may contribute to this problem. 

In a study of 10,584 individuals at high risk for CKD, Klag, Brown, and Collins (2004) examined the association between CKD and uncontrolled HTN. The Kidney Early Evaluation Program (KEEP) is a community-based program to identify people at risk for kidney disease. This includes data from individuals with a personal or family history of HTN, diabetes, and/or kidney disease. The researchers found that the prevalence of uncontrolled HTN within the group of individuals at high risk of CKD was “unacceptably high.” HTN is a modifiable risk factor for CKD; education and prevention efforts must be implemented to improve the treatment of HTN for high risk individuals.

Similarly, Boulware, Carson, Troll, Powe, and Cooper (2009) analyzed the association between perceived risk of CKD and adherence to HTN management. HTN and diabetes are the most common CKD risk factors, and even mild forms of these conditions confer several-fold increased risks of CKD. In a cross-sectional study of 195 patients enrolled in a randomized controlled trial on HTN management in Maryland, the researchers found that those with the greatest perceived susceptibility to CKD had poorer BP management adherence. Also, many patients at high risk of CKD had low perceived susceptibility. These findings suggest a lack of knowledge of CKD on the part of both patients and primary care physicians. Efforts to improve awareness and understanding of CKD could improve therapy adherence and clinical outcomes. 

Discussion

The findings of this literature review confirm the thesis that HTN impairs kidney function and increases the risk of CKD. Hardy et al. (2018) found that modest reductions in BP helped to prevent CKD. Similarly, Cao et al. (2014) found that PHTN increased the risk of CKD. Okin et al. (2016) concluded that lowering BP and treating HTN could slow the progression of renal dysfunction. HTN is a leading cause of CKD and managing BP is an essential aspect of preventing the disease. 

The studies presented also suggest that while uncontrolled BP and HTN increase the risk of CKD, patients’ perceived risk and adherence to BP management does not always reflect these findings. Klag et al. (2004) found a high prevalence of uncontrolled HTN in individuals at high risk of CKD. Similarly, Boulware et al. (2009) found that high perceived risk of CKD lead to poorer BP management, and that high actual risk of CKD lead to low perceived risk in patients. Ladi-Akinyemi and Ajayi (2017) recognized that developing countries (such as Nigeria) may not provide sufficient education on the negative effect of HTN on kidney function. These studies highlight the need for improved education for those with high BP and at high-risk of CKD.

Two studies highlighted the importance of preventing CKD in asymptomatic individuals by managing BP levels. Vanelli et al. (2018) found that relatively young and asymptomatic individuals had high BP that placed them at a higher risk of CKD. Nishikawa et al. (2015) also found that metabolic factors such as HTN could increase the risk of CKD in asymptomatic (non-obese) individuals. 

Conventional treatment for HTN generally involves pharmacological drugs, which are often associated with many side effects (Tabassum & Ahmad, 2011). Complementary and alternative medicine (CAM) treatments are gaining popularity and respect as effective and safe alternatives. One method for preventing and reversing HTN is the Dietary Approaches to Stop Hypertension (DASH) diet. The DASH diet lowers BP by reducing sodium intake and promoting healthy eating habits and weight loss. It emphasizes fruits and vegetables, lean meat and dairy products, reduced sodium intake, increased micronutrient intake, and overall consumption of minimally processed and fresh foods (Challa & Uppaluri, 2018). 

There are also many herbs that can naturally help to lower BP levels with fewer side effects than drugs. Garlic (Allium sativum), for instance, is believed to lower BP by increasing nitric oxide production, which results in smooth muscle relaxation and vasodilatation. Also, the soluble fiber in whole oats (Avena sativa) can significantly reduce BP and the need for antihypertensive medication. Chinese Hawthorn (Crataegus pinnatifida) has been used in China to lower BP for thousands of years. Hawthorn contains flavonoids and oligomeric procyanidins, two potent antioxidants that are believed to benefit the heart. Roselle (Hibiscus sabdariffa) is an extensively studied plant that has been shown to have antihypertensive properties. Linseed (Linum usitatissimum) is rich in α-linolenic acid, an omega-3 fatty acid, which can significantly lower BP in people with HTN. Finally, ginger root (Zingiber officinale) lowers BP by improving blood circulation and relaxing the muscles surrounding blood vessels (Tabassum & Ahmad, 2011).

Lifestyle modifications can also greatly improve BP levels and help prevent HTN. Maintaining a healthy weight is incredibly important for reducing HTN risk. Obesity accounts for a three times greater risk of developing HTN, and a decrease in weight by just 10 pounds can decrease BP in both normal and hypertensive individuals (Eskridge, 2010). Exercise, limitation of alcohol intake, and cessation of smoking are also important factors. It is recommended to participate in moderate intensity exercise for at least 30 minutes, most days of the week. Finally, stress management is an important aspect of BP control. Chronic stress negatively impacts many regulatory mechanisms in the body and their ability to maintain physiological homeostasis. Increased hormone secretion raises BP while the body is under stress in order to ensure that active muscles receive oxygenated blood. However, under chronic stress, this response leads to HTN and ultimately coronary heart disease (Seaward, 2018). Relaxation techniques for coping with stress and reducing BP include: meditation, yoga, T’ai Chi, music therapy, progressive muscular relaxation, autogenic training, clinical biofeedback, and spending time outdoors. 

Conclusions

The screening and treatment of apparently asymptomatic individuals is extremely important for disease prevention. As found by Vanelli et al. (2018), even a simple questionnaire could greatly help to lessen CKD risk over a population. Early detection may be a key component to preventing CKD and could greatly reduce the financial and physical burden that it places on a society. 

HTN is a modifiable risk factor for CKD; education and prevention efforts must be implemented to improve the treatment of HTN for high-risk individuals. High-risk patients may not recognize the severe consequences of HTN, whereas patients who believe they are at risk of CKD may demonstrate poor adherence to BP management. This problem may be amplified in developing countries where healthcare is less consistent and patients are less likely to seek professional medical advice until disease symptoms are already present. It is extremely important to address this problem by accessing and informing this high-risk population worldwide. Finally, with few side effects and significant health benefits, CAM therapies such as the DASH diet, physical exercise, herbal remedies, and stress management programs should be widely promoted to hypertensive patients in order to reduce the incidence of HTN and CKD. 

References

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