Chronic diseases are the leading cause of death and disability worldwide. According to the World Health Organization, 88 percent of deaths in the United States in 2002 were attributable to chronic disease. Prevention of the onset or progression of chronic disease is often promoted as the gold standard, although the optimal interventions to achieve this have not been well documented. A number of lifestyle behaviors contribute to overall morbidity and mortality of chronic disease. Among these, physical activity and diet have been identified as two modifiable risk factors that may impact onset or progression of disease.
Previous research has suggested that improved diet may decrease the burden of chronic disease, particularly coronary heart disease. However, the benefits of lifestyle modifications in preventing progression or recurrence of disease is not as well documented. In addition, it remains unclear how effective interventions are in modifying risk factors, and which chronic diseases, if any, would benefit.
The chronic diseases examined in this review are type 2 diabetes, metabolic syndrome, breast and prostate cancer. Type 2 diabetes is a major cause of morbidity and mortality. Diabetes was the seventh leading cause of death in the U.S. in 2006; cardiovascular disease (CVD) accounted for more than 65 percent of all diabetic deaths. Diabetes is also the leading cause of kidney failure, nontraumatic lower-extremity amputations, and blindness among adults in the U.S.
Metabolic syndrome is defined as a constellation of interrelated metabolic risk factors that promote the development of CVD and type 2 diabetes. The most widely recognized metabolic risk factors are dyslipidemia, elevated plasma glucose, and hypertension. Its clinical utility for risk prediction is controversial. Prediabetes, which includes impaired fasting glucose (IFG) and impaired glucose tolerance (IGT), has been suggested to be equally effective in identifying those at risk of developing type 2 diabetes. Our operational definition of metabolic syndrome included metabolic syndrome, insulin resistance, prediabetes, IFG, IGT, syndrome X, dysmetabolic syndrome X, and Reaven syndrome. Approximately 64 million or 25 percent of adults in the U.S. had metabolic syndrome in 2000. As of 2011, the American Diabetes Association estimated that 57 million people in the U.S. had prediabetes.
Many risk factors for the development of metabolic syndrome have been proposed, one of which is obesity. Additional risk factors include increasing age and physical inactivity.
Breast cancer is defined as the development of malignant cells in the breast which usually originate from the ducts or lobules of the breast. The National Cancer Institute estimates that in 2010 there will be 209,060 new cases of breast cancer diagnosed, with 40,230 deaths. Survival and recurrence rates depend on a number of factors including stage of the cancer at diagnosis. There is a strong correlation between obesity and increased risk of breast cancer. Studies have suggested that increased physical activity reduces the incidence of breast cancer. A recent systematic review found that physical activity could reduce the incidence of breast cancer in postmenopausal women by 20 to 80 percent.
Prostate cancer. Prostate cancer is defined as a malignant growth of cells in the prostate gland. It is the second leading cause of death of males in the U.S. It is estimated that 217,730 men will be diagnosed with and 32,050 will die of prostate cancer in the U.S. in 2010. The impact of lifestyle factors on the incidence or recurrence of prostate cancer is unclear. Results from studies of the association between dietary intake and risk of prostate cancer are inconsistent. Research has shown an association between body mass index (BMI) and incidence of prostate cancer. The effect of physical activity on the incidence prostate cancer continues to be debated.