Cystic Fibrosis: Overview and Risk Factors

Cystic fibrosis (CF) is a hereditary disease that affects many parts of the body. The condition requires extensive treatment, and the average age of survival, while improving, is currently just 35 years.

The disease is caused by a gene mutation that results in thickened secretions of the body's glands, including sweat glands, parts of the digestive tract, the sinuses, and the airways. As a result, glands and passageways become clogged, leading to respiratory and digestive symptoms, among other problems.

CF is the most common genetic disorder in North America. In the United States, approximately 30,000 individuals have the condition. CF is also one of the most common causes of poor nutrient absorption in children. Because normal absorption and digestion of nutrients are required for proper growth, failure to thrive, malnutrition, and growth retardation are common in children who are not appropriately treated.

Symptoms

• Frequent cough, which is dry at first, then productive of phlegm or blood.
• Lung infections: Symptoms may include cough, fever, aches, loss of appetite, and difficulty breathing.
• Other respiratory problems such as wheezing and shortness of breath
• Vomiting
• Constipation
• Malnutrition
• Diabetes
• Poor growth
• Fatigue
• Male infertility: Women may have some abnormalities of the cervical mucus, but fertility does not appear to be significantly reduced.

Risk Factors

• Genetics: CF is a hereditary condition caused by a genetic trait. A family history of CF and unexplained infant death are risk factors.
• Race: CF occurs in approximately 1 in 2,500 Caucasians, 1 in 15,000 African-Americans, and 1 in 30,000 Asian-Americans.

Diagnosis

• Individuals with a family history of CF should have genetic testing. Prenatal testing and newborn screening may be used. Early detection can make it easier to manage the disease.
  
• In suspected cases, a medical history and physical examination will be the initial steps.
  
• Cystic fibrosis is diagnosed by a sweat test (which can be done as early as 48 hours of age). The test measures the levels of salt and chloride in the individual's sweat. Affected patients have significantly increased levels. A positive sweat test combined with lung and/or digestive symptoms establishes the diagnosis in nearly all cases.
  
• Stool tests to identify excess fat in the stools can be used to screen for poor digestion and absorption of fat, which are hallmarks of this disease. However, a sweat test or genetic testing is necessary for definitive diagnosis.

Treatment

The cornerstones of treatment are antibiotics, respiratory therapy to keep the airways clear of mucus, and nutritional support. CF patients should be cared for at a comprehensive CF care center by a multidisciplinary health care team that includes a physician, nurse, respiratory therapist, dietitian, and social worker.

• Antibiotics, such as azithromycin and tobramycin, are used both for treatment and prevention of lung infections. 
• Steroids may reduce airway inflammation. They can be administered as pills or inhalers.
  
• Chest physical therapy should be performed daily to assist with clearing mucus from the airways. In addition, a medication called dornase alfa (Pulmozyme) decreases the thickness of the sputum, making it easier to clear from the airways.
  
• Bronchodilator inhalers, similar to those used in treating asthma, are appropriate in CF as well.
  
• Participation in regular exercise may improve lung function. A review of exercise benefits indicated that over three years of physical training, the patients who exercised regularly had significantly better lung function than those who did not. Both aerobic exercise and resistance exercise appear to benefit CF patients, and both forms of exercise should be encouraged.
  
• Digestive enzyme supplements are generally required in all patients to allow for the digestion of fats.
  
• A significant percentage of adults with the disease will develop diabeteshttp://www.nutritionmd.org/consumers/endocrinology/diabetes.html mellitus, which requires insulin treatment and individualized dietary advice.
  
• Constipation can be treated with a laxative, such as polyethylene glycol (MiraLax) or polyethylene glycol plus electrolytes (Golytely).
• In advanced disease, lung transplantation is an option. It should be considered in patients who are no longer responding to other therapies.

Cystic Fibrosis: Nutritional Considerations

Nutritional management has a dramatic effect on growth and survival in patients with CF.  The following considerations are key:

• Sufficient caloric intake: Survival is much better in patients who are nearer their normal weight. A study of adults with CF found that 60 percent failed to meet recommended calorie needs, and 72 percent failed to meet recommendations for both protein and calories. Thus, a high-energy diet is commonly recommended, along with nutritional supplements.
  
  With proper nutrition therapy, including a calorie intake of 20 to 50 percent more than the Estimated Energy Requirement (EER), patients with CF may grow normally. Although nutritional supplements have been used in an attempt to attain this goal, research does not support their use. Instead, high-fat diets have typically been used, although the benefit of this approach is not yet been proven either. The kind of fat that should be consumed is also under debate.
  
  Although a diet high in fat (including animal fat) is often recommended, it has disadvantages for patients with CF. The omega-6 fatty acids found in these foods may adversely affect CF patients by encouraging­ inflammation in the lungs. In contrast, omega-3 fats appear to be of clinical benefit in patients with CF. Reduction of sputum, improved lung function, a decrease in inflammation, and a decreased need for antibiotics have been observed in patients who have taken omega-3 fatty acid supplements.
  
  Increasing the intake of plant sources of omega-3 fats (e.g., flax seed and flax oil) and monounsaturated fats (e.g., olive oil) has been suggested as an approach to improving fatty acid nutrition in CF patients. The Cystic Fibrosis Foundation consensus panel has made similar recommendations, suggesting that oils rich in both omega-3 and monounsaturated fats (e.g., flax, canola, and soy) benefit CF patients.
  
• Nutritional adequacy: Patients should be monitored for evidence of vitamin deficiency and treated accordingly. CF patients require supplemental nutrients for various reasons. The fat-soluble vitamins A, D, E, and K are a priority, mainly because digestive enzyme insufficiency often results in poor absorption of these nutrients.
  
  Deficiencies of antioxidants (e.g., vitamin C) and low concentrations of antioxidant enzymes (e.g., glutathione peroxidase) have been found in CF patients, along with low levels of selenium and zinc. CF patients are also at risk for low levels of iron, calcium, and sodium.
• Vitamin A and carotenoids
  Deficiency of vitamin A occurs in 15 to 40 percent of CF patients, in spite of enzyme replacement and use of low-dose vitamin A supplements (2,500 to 4,000 International Units, or IU, a day). Supplementation of up to 12,000 IU of vitamin A per day may become necessary. Carotenoids are also poorly absorbed in CF patients, and lycopene, alpha-carotene, and beta-carotene concentrations appear significantly lower than in healthy patients.
  
• Vitamin D
  Deficiency of vitamin D occurs in 10 to 40 percent of children with CF, and in more than 81 percent of adults with this condition. Lack of vitamin D aggravates the already greater risk for osteoporosis and fractures seen in CF patients. Low concentrations of vitamin D have been found in patients with CF taking 1,000 IU of vitamin D per day, and the deficiency may not even be completely corrected even with megadoses of the vitamin.
  
• Vitamin E
  Deficiency of vitamin E occurs in 87 percent of unsupplemented patients with CF. The amount suggested for supplementation is 200 milligrams a day.
  
• Vitamin K
  Deficiency of vitamin K has been found in 81 percent of patients with CF. Vitamin K supplementation of 1 milligram a day is recommended.