Chronic Kidney Disease: Overview and Risk Factors
Chronic kidney disease (CKD), which is also known as kidney failure or renal insufficiency, is an exceedingly common disorder among older adults. Normally, the kidneys filter the blood, excrete toxins and waste, and maintain electrolyte balance. When kidney function is compromised, these actions are impaired, which can result in fatal consequences.
The majority of cases are due to long-standing diabetes mellitus and/or hypertension. These diseases damage the blood vessels of the kidneys, causing kidney dysfunction.
Few symptoms are noticeable until about 75 percent of kidney function has been lost. Initial symptoms may include fluid retention, swelling of the legs, hypertension, and anemia. As kidney function is further compromised, more severe symptoms develop, including shortness of breath, nausea, vomiting, weight loss, confusion, and severe itching.
Kidney disease is also a major risk factor for heart disease. Indeed, most patients with chronic kidney disease die from cardiovascular disease even before they develop advanced kidney disease.
African-Americans have a significantly higher rate of kidney disease than other racial groups. This is partly due to higher rates of hypertension in this group.
Other factors associated with an increased risk include:
- Older age
- Family history
- Urinary tract infections and kidney stones
- Other medical disorders that may increase the risk of kidney damage include diabetes mellitus, hypertension, autoimmune disorders (e.g., systemic lupus erythematosus), and systemic infections.
- Medications, including nonsteroidal anti-inflammatory drugs (e.g., ibuprofen)
- Tobacco smoking
- The evaluation will begin with a medical history and a physical examination
- Blood testing will be performed.
- Urine testing will also be performed.
- Ultrasound or CT scan may be necessary to determine the underlying cause.
- Rarely, a kidney biopsy may be necessary.
- Specific treatments that address the underlying cause of kidney disease may halt the loss of kidney function. In particular, patients with diabetes mellitus or hypertension should be treated aggressively to control blood sugar and blood pressure. Angiotensin-converting enzyme (ACE) inhibitors, such as lisinopril or captopril, are especially helpful blood pressure medications for individuals with kidney disease.
- Sodium restriction and/or diuretics are usually needed to reduce fluid retention and swelling.
- Anemia is common in kidney disease patients. In patients with iron deficiency, supplemental iron should be used. Patients with advanced kidney disease are usually treated with a medication called erythropoietin.
- Exercise, both in the form of resistance training and aerobic exercise, can help patients with kidney disease.
- Ultimately, dialysis or kidney transplantation may be necessary.
Chronic Kidney Disease: Nutritional Considerations
Managing kidney disease presents a nutritional challenge. Patients with kidney disease frequently have risk factors for atherosclerosis, which would benefit from a diet that is low in fat, sodium, and sugar, and high in fiber. However, patients also commonly show signs of malnutrition, which calls for a less restricted meal plan. The right kind of diet, as described below, can help control blood pressure, cholesterol, and the buildup of waste products in the blood, slow the progression of kidney disease, and may prevent cardiovascular disease.
- Decreased protein intake: Prolonged high protein intake may compromise kidney function. In women with mild kidney disease, those with the highest protein intake had more than three times increased risk for developing a 15 percent or great decrease in kidney function, compared with those eating the least protein. This effect was attributed to nondairy animal (not vegetable) sources of protein.
Evidence for the benefit of a low-protein diet is not conclusive. Some studies suggest that restricting protein intake may help delay the need for kidney dialysis or transplantation. One study, the Modification of Diet in Renal Disease (MDRD) study, did not reveal a significant benefit. However, a later analysis of five studies (including the MDRD Study) reported a roughly 35 percent lower risk for kidney failure or death on a low-protein diet. A more recent review based on eight trials and including a total of 1,524 patients indicated that, although the optimal protein intake remains unknown, reducing protein intake in individuals with kidney disease may reduce mortality from this disease by 30 percent, compared with higher or unrestricted protein intake.
In patients with severe kidney disease, very low-protein diets supplemented with essential amino acids can be effective.
- Sodium restriction: Higher blood pressure is a known cause for kidney disease, and sodium restriction is an important part of blood pressure control. Although additional clinical trials are required, evidence indicates that patients with chronic kidney disease who follow low-salt diets have half the rate of decline in kidney function as those who follow high-sodium diets.
- Water-soluble vitamins: Low-protein diets may increase the risk for deficiency of several vitamins, including thiamine, riboflavin, and especially pyridoxine. In addition, vitamin C levels are often low in kidney disease patients. Thus, for kidney disease patients not on kidney dialysis, supplementation with 5 mg per day of pyridoxine and 30 to 50 mg per day of vitamin C has been suggested. However, no standard recommendations for amounts of thiamine or riboflavin exist for this group of individuals.
- Vitamin D supplementation: Deficiency of vitamin D generally occurs early in the course of kidney disease. Supplementation with vitamin D is an important action to prevent cardiovascular disease.
- A diet high in fiber and low in saturated fat and cholesterol: Most patients with chronic kidney disease die from cardiovascular causes before developing advanced kidney disease. In a significant number of patients, treatment of cholesterol - by diet or medications - may decrease the progression of kidney disease. Studies show that a vegetarian diet can be particularly helpful in reducing cholesterol.
Dietary and supplemental sources of fiber may be helpful for reducing the buildup of waste products in the blood that cause many symptoms of kidney disease.
- A high-calorie diet: Loss of appetite and poor food intake is common in these patients. Malnutrition is associated with poor outcome and a higher risk of death in patients with kidney disease.
- Omega-3 fatty acid supplements: Omega-3 fatty acid supplements are under study. Some results have been encouraging. Nevertheless, more study is required before they can be considered an effective treatment.